inflater(...)源码解析

以ListView来演示，下面为三种为item的View填充的方法
- view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item, null);
- view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item, new LinearLayout(MainActivity.this), true);
- view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item, new LinearLayout(MainActivity.this), false);

item的布局文件

<Button xmlns:android="http://schemas.android.com/apk/res/android"        android:layout_width="120dp"        android:layout_height="120dp"        android:orientation="vertical"        android:text="这里"></Button>

效果图

1. 第一种：布局文件最外层设置无效
2. 第二种：root不为空attachToRoot为true，布局文件最外层设置有效

3. 第三种：root不为空attachToRoot为false，布局文件最外层设置有效

   源码分析

 public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {        synchronized (mConstructorArgs) {            Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");            final Context inflaterContext = mContext;            final AttributeSet attrs = Xml.asAttributeSet(parser);            Context lastContext = (Context) mConstructorArgs[0];            mConstructorArgs[0] = inflaterContext;            View result = root;            try {                // Look for the root node.                int type;                while ((type = parser.next()) != XmlPullParser.START_TAG &&                        type != XmlPullParser.END_DOCUMENT) {                    // Empty                }                if (type != XmlPullParser.START_TAG) {                    throw new InflateException(parser.getPositionDescription()                            + ": No start tag found!");                }                final String name = parser.getName();                if (DEBUG) {                    System.out.println("**************************");                    System.out.println("Creating root view: "                            + name);                    System.out.println("**************************");                }                if (TAG_MERGE.equals(name)) {                    if (root == null || !attachToRoot) {                        throw new InflateException("<merge /> can be used only with a valid "                                + "ViewGroup root and attachToRoot=true");                    }                    rInflate(parser, root, inflaterContext, attrs, false);                } else {                    // Temp is the root view that was found in the xml                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);                    ViewGroup.LayoutParams params = null;                    if (root != null) {                        if (DEBUG) {                            System.out.println("Creating params from root: " +                                    root);                        }                        // Create layout params that match root, if supplied                        params = root.generateLayoutParams(attrs);                        if (!attachToRoot) {                            // Set the layout params for temp if we are not                            // attaching. (If we are, we use addView, below)                            temp.setLayoutParams(params);                        }                    }                    if (DEBUG) {                        System.out.println("-----> start inflating children");                    }                    // Inflate all children under temp against its context.                    rInflateChildren(parser, temp, attrs, true);                    if (DEBUG) {                        System.out.println("-----> done inflating children");                    }                    // We are supposed to attach all the views we found (int temp)                    // to root. Do that now.                    if (root != null && attachToRoot) {                        root.addView(temp, params);                    }                    // Decide whether to return the root that was passed in or the                    // top view found in xml.                    if (root == null || !attachToRoot) {                        result = temp;                    }                }            } catch (XmlPullParserException e) {                InflateException ex = new InflateException(e.getMessage());                ex.initCause(e);                throw ex;            } catch (Exception e) {                InflateException ex = new InflateException(                        parser.getPositionDescription()                                + ": " + e.getMessage());                ex.initCause(e);                throw ex;            } finally {                // Don't retain static reference on context.                mConstructorArgs[0] = lastContext;                mConstructorArgs[1] = null;            }            Trace.traceEnd(Trace.TRACE_TAG_VIEW);            return result;        }    }

• 三种情况最终都会来到以上代码块进行最后的处理

参数分析

1. parser：item的布局文件经过XmlPullParaer之后的
2. root：inflater中传入的父布局文件
3. attachToRoot：inflater中传入的boolean类型

关键代码

• 第9行：初始化result，携带root引用，该属性为最终返回值
• 第42行：获取item中的最顶层的view，初始化temp并获得引用
• 第46~58行：若root不为空，则获取temp中的attrs,之后再次判断是否attach to root，若为false，则在此temp.setLayoutParams（attrs）,若为true，看注释
• 第65行：将item中的子view填充进temp中
• 第73~75行：在root不为空，并且attachToRoot为True的情况下，将temp和attrs添加到root中
• 第79~81行：在root为空或者attachToRoot为false的情况下，result=temp并且最终返回

分析

1. 第一种：因为root为空，而attachToRoot为false，所以丢失了item中顶层的attrs属性
2. 第二种：root不为空，attachToRoot为true，通过root.addView(temp,attrs)，所以attrs属性没丢失
3. 第三种：root不为空，attachToRoot为false，通过temp.setLayoutParams（attrs），所以attrs属性没丢失

注意点

1. temp.setLayoutParams（attrs）：该方法为设置该View在父类中的位置属性，例如layout_width