Android View面试难点解析
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1.View的绘制流程分几步，从哪开始？哪个过程结束以后能看到view？
答：从ViewRoot的performTraversals开始，经过measure，layout,draw 三个流程。draw流程结束以后就可以在屏幕上看到view了
2.view的测量宽高和实际宽高有区别吗？
答：基本上百分之99的情况下都是可以认为没有区别的。有两种情况，有区别。第一种 就是有的时候会因为某些原因 view会多次测量，那第一次测量的宽高 肯定和最后实际的宽高 是不一定相等的，但是在这种情况下
最后一次测量的宽高和实际宽高是一致的。此外，实际宽高是在layout流程里确定的，我们可以在layout流程里 将实际宽高写死 写成硬编码，这样测量的宽高和实际宽高就肯定不一样了，虽然这么做没有意义 而且也不好。
3.view的measureSpec 由谁决定?顶级view呢？
答：由view自己的layoutparams和父容器 一起决定自己的measureSpec。一旦确定了spec，onMeasure中就可以确定view的宽高
顶级view就稍微特殊一点，对于decorView的测量在ViewRootImpl的源码里。
//desire的这2个参数就代表屏幕的宽高，
childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);
childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//decorView的measureSpec就是在这里确定的，其实比普通view的measurespec要简单的多</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//代码就不分析了 一目了然的东西</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getRootMeasureSpec</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> windowSize, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> rootDimension) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> measureSpec; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (rootDimension) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> ViewGroup.LayoutParams.MATCH_PARENT: <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Window can't resize. Force root view to be windowSize.</span> measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> ViewGroup.LayoutParams.WRAP_CONTENT: <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Window can resize. Set max size for root view.</span> measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">default</span>: <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Window wants to be an exact size. Force root view to be that size.</span> measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> measureSpec;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li></ul>4、对于普通view来说，他的measure过程中，与父view有关吗？如果有关，这个父view也就是viewgroup扮演了什么角色？
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">/对于普通view的measure来说 是由这个view的 父view ，也就是viewgroup来触发的。<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//也就是下面这个measureChildWithMargins方法</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">measureChildWithMargins</span>(View child, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> parentWidthMeasureSpec, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> widthUsed, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> parentHeightMeasureSpec, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> heightUsed) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//第一步 先取得子view的 layoutParams 参数值 </span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//然后开始计算子view的spec的值，注意这里看到 计算的时候除了要用子view的 layoutparams参数以外</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//还用到了父view 也就是viewgroup自己的spec的值</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin + widthUsed, lp.width); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec, mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin + heightUsed, lp.height); child.measure(childWidthMeasureSpec, childHeightMeasureSpec);}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这个算view的spec的方法 看上去一大串 但是真的逻辑非常简单 就是根据父亲viewgroup</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//的meaurespec 同时还有view自己的params来确定 view自己的measureSpec。</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//注意这里的参数是padding,这个值的含义是 父容器已占用的控件的大小 所以view的Specsize</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//的值 你们可以看到 是要减去这个padding的值的。总大小-已经用的 =可用的。 很好理解。</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//然后就是下面的switch逻辑 要自己梳理清楚。其实也不难，主要是下面几条原则</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果view采用固定宽高，也就是写死的数值那种。那就不管父亲的spec的值了，view的spec 就肯定是exactly 并且大小遵循layout参数里设置的大小。</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果view的宽高是match_parent ，那么就要看父容器viewgroup的 spec的值了，如果父view的spec是exactly模式，</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//那view也肯定是exactly,并且大小就是父容器剩下的空间。如果父容器是at_most模式，那view也是at_most 并且不会超过剩余空间大小</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//如果view的宽高是wrap_content, 那就不管父容器的spec了，view的spec一定是at_most 并且不会超过父view 剩余空间的大小。</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getChildMeasureSpec</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> spec, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> padding, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> childDimension) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> specMode = MeasureSpec.getMode(spec); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> specSize = MeasureSpec.getSize(spec); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> size = Math.max(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, specSize - padding); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> resultSize = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> resultMode = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (specMode) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Parent has imposed an exact size on us</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> MeasureSpec.EXACTLY: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { resultSize = childDimension; resultMode = MeasureSpec.EXACTLY; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension == LayoutParams.MATCH_PARENT) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants to be our size. So be it.</span> resultSize = size; resultMode = MeasureSpec.EXACTLY; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension == LayoutParams.WRAP_CONTENT) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants to determine its own size. It can't be</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// bigger than us.</span> resultSize = size; resultMode = MeasureSpec.AT_MOST; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Parent has imposed a maximum size on us</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> MeasureSpec.AT_MOST: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants a specific size... so be it</span> resultSize = childDimension; resultMode = MeasureSpec.EXACTLY; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension == LayoutParams.MATCH_PARENT) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants to be our size, but our size is not fixed.</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Constrain child to not be bigger than us.</span> resultSize = size; resultMode = MeasureSpec.AT_MOST; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension == LayoutParams.WRAP_CONTENT) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants to determine its own size. It can't be</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// bigger than us.</span> resultSize = size; resultMode = MeasureSpec.AT_MOST; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Parent asked to see how big we want to be</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> MeasureSpec.UNSPECIFIED: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants a specific size... let him have it</span> resultSize = childDimension; resultMode = MeasureSpec.EXACTLY; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension == LayoutParams.MATCH_PARENT) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants to be our size... find out how big it should</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// be</span> resultSize = View.sUseZeroUnspecifiedMeasureSpec ? <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> : size; resultMode = MeasureSpec.UNSPECIFIED; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (childDimension == LayoutParams.WRAP_CONTENT) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Child wants to determine its own size.... find out how</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// big it should be</span> resultSize = View.sUseZeroUnspecifiedMeasureSpec ? <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> : size; resultMode = MeasureSpec.UNSPECIFIED; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> MeasureSpec.makeMeasureSpec(resultSize, resultMode); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; 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padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li><li style="box-sizing: border-box; padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li><li style="box-sizing: border-box; padding: 0px 5px;">98</li><li style="box-sizing: border-box; padding: 0px 5px;">99</li><li style="box-sizing: border-box; padding: 0px 5px;">100</li><li style="box-sizing: border-box; padding: 0px 5px;">101</li><li style="box-sizing: border-box; padding: 0px 5px;">102</li><li style="box-sizing: border-box; padding: 0px 5px;">103</li><li style="box-sizing: border-box; padding: 0px 5px;">104</li><li style="box-sizing: border-box; padding: 0px 5px;">105</li><li style="box-sizing: border-box; padding: 0px 5px;">106</li><li style="box-sizing: border-box; padding: 0px 5px;">107</li></ul>5.view的meaure和onMeasure有什么关系？
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">/view的measure是final 方法 我们子类无法修改的。 <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> final <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">measure</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> widthMeasureSpec, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> heightMeasureSpec) { boolean optical = isLayoutModeOptical(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (optical != isLayoutModeOptical(mParent)) { Insets insets = getOpticalInsets(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oWidth = insets.left + insets.right; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> oHeight = insets.top + insets.bottom; widthMeasureSpec = MeasureSpec.adjust(widthMeasureSpec, optical ? -oWidth : oWidth); heightMeasureSpec = MeasureSpec.adjust(heightMeasureSpec, optical ? -oHeight : oHeight); } <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Suppress sign extension for the low bytes</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> key = (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span>) widthMeasureSpec << <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span> | (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span>) heightMeasureSpec & <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0xffffffff</span>L; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mMeasureCache == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) mMeasureCache = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> LongSparseLongArray(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT || widthMeasureSpec != mOldWidthMeasureSpec || heightMeasureSpec != mOldHeightMeasureSpec) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// first clears the measured dimension flag</span> mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET; resolveRtlPropertiesIfNeeded(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> cacheIndex = (mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT ? -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> : mMeasureCache.indexOfKey(key); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (cacheIndex < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> || sIgnoreMeasureCache) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// measure ourselves, this should set the measured dimension flag back</span> onMeasure(widthMeasureSpec, heightMeasureSpec); mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span> = mMeasureCache.valueAt(cacheIndex); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Casting a long to int drops the high 32 bits, no mask needed</span> setMeasuredDimensionRaw((<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>) (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span> >> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span>), (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span>); mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// flag not set, setMeasuredDimension() was not invoked, we raise</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// an exception to warn the developer</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> ((mPrivateFlags & PFLAG_MEASURED_DIMENSION_SET) != PFLAG_MEASURED_DIMENSION_SET) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IllegalStateException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"View with id "</span> + getId() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": "</span> + getClass().getName() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"#onMeasure() did not set the"</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" measured dimension by calling"</span> + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" setMeasuredDimension()"</span>); } mPrivateFlags |= PFLAG_LAYOUT_REQUIRED; } mOldWidthMeasureSpec = widthMeasureSpec; mOldHeightMeasureSpec = heightMeasureSpec; mMeasureCache.put(key, ((<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span>) mMeasuredWidth) << <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span> | (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span>) mMeasuredHeight & <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0xffffffff</span>L); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// suppress sign extension</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//不过可以看到的是在measure方法里调用了onMeasure方法</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//所以就能知道 我们在自定义view的时候一定是重写这个方法！</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onMeasure</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> widthMeasureSpec, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> heightMeasureSpec) { setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec), getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec)); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li></ul>6.简要分析view的measure流程？
答：先回顾问题4，viewgroup 算出子view的spec以后 会调用子view的measure方法，而子view的measure方法 我们问题5也看过了实际上是调用的onMeasure方法
所以我们只要分析好onMeasure方法即可，注意onMeasure方法的参数 正是他的父view算出来的那2个spec的值(这里view的measure方法会把这个spec里的specSize值做略微的修改 这个部分 不做分析 因为measure方法修改specSize的部分很简单)。
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//可以看出来这个就是setMeasuredDimension方法的调用 这个方法看名字就知道就是确定view的测量宽高的</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//所以我们分析的重点就是看这个getDefaultSize 方法 是怎么确定view的测量宽高的</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onMeasure</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> widthMeasureSpec, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> heightMeasureSpec) { setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec), getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec)); }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这个方法特别简单 基本可以认为就是近似的返回spec中的specSize，除非你的specMode是UNSPECIFIED</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//UNSPECIFIED 这个一般都是系统内部测量才用的到，这种时候返回size 也就是getSuggestedMinimumWidth的返回值</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getDefaultSize</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> size, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> measureSpec) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> result = size; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> specMode = MeasureSpec.getMode(measureSpec); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> specSize = MeasureSpec.getSize(measureSpec); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">switch</span> (specMode) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> MeasureSpec.UNSPECIFIED: result = size; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> MeasureSpec.AT_MOST: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">case</span> MeasureSpec.EXACTLY: result = specSize; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> result;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//跟view的背景相关 这里不多做分析了</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">getSuggestedMinimumWidth</span>() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> (mBackground == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) ? mMinWidth : max(mMinWidth, mBackground.getMinimumWidth()); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul>7.自定义view中 如果onMeasure方法 没有对wrap_content 做处理 会发生什么？为什么？怎么解决？
答：如果没有对wrap_content做处理 ，那即使你在xml里设置为wrap_content.其效果也和match_parent相同。看问题4的分析。我们可以知道view自己的layout为wrap，那mode就是at_most（不管父亲view是什么specmode）.
这种模式下宽高就是等于specSize(getDefaultSize函数分析可知)，而这里的specSize显然就是parentSize的大小。也就是父容器剩余的大小。那不就和我们直接设置成match_parent是一样的效果了么？
解决方式就是在onMeasure里 针对wrap 来做特殊处理 比如指定一个默认的宽高，当发现是wrap_content 就设置这个默认宽高即可。
8.ViewGroup有onMeasure方法吗？为什么?
没有，这个方法是交给子类自己实现的。不同的viewgroup子类 肯定布局都不一样，那onMeasure索性就全部交给他们自己实现好了。
9.为什么在activity的生命周期里无法获得测量宽高？有什么方法可以解决这个问题吗？
答：因为measure的过程和activity的生命周期 没有任何关系。你无法确定在哪个生命周期执行完毕以后 view的measure过程一定走完。可以尝试如下几种方法 获取view的测量宽高。
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//重写activity的这个方法</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onWindowFocusChanged</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> hasFocus) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onWindowFocusChanged(hasFocus); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (hasFocus) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> width = tv.getMeasuredWidth(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> height = tv.getMeasuredHeight(); Log.v(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"burning"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"width=="</span> + width); Log.v(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"burning"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"height=="</span> + height); } }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>将一个runnable添加到Layout队列中：View.post()
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Override <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onStart</span>() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span>.onStart(); tv.post(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> width = tv.getMeasuredWidth(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> height = tv.getMeasuredHeight(); } }); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>监听view的视图树，这个方法会调用很多次的
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">view.getViewTreeObserver().addOnGlobalLayoutListener(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ViewTreeObserver.OnGlobalLayoutListener() { <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onGlobalLayout</span>() { mScrollView.post(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() { view.getHeight(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//height is ready</span> } }); } });</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>再或者
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">measure(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)；或重新调用onmeasure方法，宽高的增加值为<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> width = view.getMeasuredWidth(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> height = view.getMeasuredHeight();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
10.layout和onLayout方法有什么区别？
答：layout是确定本身view的位置 而onLayout是确定所有子元素的位置。layout里面 就是通过serFrame方法设设定本身view的 四个顶点的位置。这4个位置以确定 自己view的位置就固定了
11.setWillNotDraw方法有什么用？
答：这个方法在view里。
<code class="hljs applescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">/** * If this view doesn't do any drawing <span class="hljs-function_start" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">on</span></span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">its</span> own, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span> this flag <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> * allow further optimizations. By default, this flag <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span> <span class="hljs-function_start" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">on</span></span> * View, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">but</span> could be <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span> <span class="hljs-function_start" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">on</span></span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">some</span> View subclasses such <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">as</span> ViewGroup. * * Typically, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> you override {@link <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#onDraw(android.graphics.Canvas)}</span> * you should clear this flag. * * @param willNotDraw whether <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">or</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> this View draw <span class="hljs-function_start" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">on</span></span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">its</span> own */ public void setWillNotDraw(<span class="hljs-type" style="box-sizing: border-box;">boolean</span> willNotDraw) { setFlags(willNotDraw ? WILL_NOT_DRAW : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, DRAW_MASK); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>用于设置标志位的 也就是说 如果你的自定义view 不需要draw的话，就可以设置这个方法为true。这样系统知道你这个view 不需要draw 可以优化执行速度。viewgroup 一般都默认设置这个为true，因为viewgroup多数都是只负责布局
不负责draw的。而view 这个标志位 默认一般都是关闭的
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