FramLayout源码分析

来源：互联网发布：网络外卖订餐系统编辑：程序博客网时间：2024/05/22 08:19

5.4.2 绘制分析

FrameLayout继承自ViewGroup，属于view控件，因此也遵从view的绘制逻辑。

根据我们对view的理解，其绘制大体也是按measure—layout—draw的流程处理的。

5.4.2.1 Measure过程

重载onMeasure，功能分3大部分：

1.遍历子view，完成每个子view的measure；

2.找到子view的最大尺寸，设置给FrameLayout，因为FrameLayout的说明里提到子view的最大尺寸就是FrameLayout的尺寸；

3.如果FrameLayout不是确定大小的模式，子view又是MATCH_PARENT属性的，则要单独为这些子view重新计算尺寸，重新measure。

分析：一开始不知道Framelayout的大小，只能根据子View的确定FrameLayout的大小，FrameLayout大小确认后，就可以确认match_parent的View的大小；

从性能分析的角度看，单独重新measure MATCH_PARENT属性的view是耗时的，这个影响有多大，需要进行实验验证。如果对性能有一定影响，那么我们在设置FrameLayout属性和其子viewMATCH_PARENT属性时就要考虑是注重于性能，还是注重于布局的兼容性。

5.4.2.2 Layout过程

这里重载了onLayout（）方法，

其layout过程就是遍历所有子view的layout方法。

其执行流程是FrameLayout. onLayout--viewGroup.layout

--view.layout--FrameLayout的成员view.onLayout--…，这样就遍历完了FrameLayout节点下的整个view树。

在FrameLayout. onLayout里遍历每个成员view的时候，还根据gravity为成员view重新计算了坐标值。

从性能优化方面考虑，因为在代码里面gravity有默认值，所以FrameLayout的成员view是否设置gravity属性，并不影响其处理速度，同时，在onLayout里对gravity的处理并不是一个耗时流程。

5.4.2.3 Draw过程

重载了draw方法，实现两个功能，第一是使用了父类的draw方法，绘制控件本身；第二是绘制Foreground，对于Foreground需要的时候再单独分析。

/** * {@inheritDoc} */@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {    int count = getChildCount();    // FrameLayout的宽或者高有一个不是精确模式的，即Framlayout的大小是不确定的    final boolean measureMatchParentChildren =            MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.EXACTLY ||            MeasureSpec.getMode(heightMeasureSpec) != MeasureSpec.EXACTLY;    mMatchParentChildren.clear();    int maxHeight = 0;    int maxWidth = 0;    int childState = 0;    //遍历子view，完成每个子view的measure；    for (int i = 0; i < count; i++) {        final View child = getChildAt(i);        if (mMeasureAllChildren || child.getVisibility() != GONE) {            measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);//测量子View
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();
            maxWidth = Math.max(maxWidth,                    child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin);            maxHeight = Math.max(maxHeight,                    child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin);            childState = combineMeasuredStates(childState, child.getMeasuredState());//????            if (measureMatchParentChildren) {                if (lp.width == LayoutParams.MATCH_PARENT ||                        lp.height == LayoutParams.MATCH_PARENT) {                    mMatchParentChildren.add(child);//把子View中宽高是Match_parent的都放入list中                }            }        }    }    // Account for padding too    maxWidth += getPaddingLeftWithForeground() + getPaddingRightWithForeground();    maxHeight += getPaddingTopWithForeground() + getPaddingBottomWithForeground();    // Check against our minimum height and width    maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());    maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());    // Check against our foreground's minimum height and width    final Drawable drawable = getForeground();    if (drawable != null) {        maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());        maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());    }    //设置FrameLayout的测量值
    setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),            resolveSizeAndState(maxHeight, heightMeasureSpec,                    childState << MEASURED_HEIGHT_STATE_SHIFT));
    //FrameLayout大小不确定时，子View的属性为match_parent时，需要重新计算子View的宽高
    count = mMatchParentChildren.size();    if (count > 1) {        for (int i = 0; i < count; i++) {            final View child = mMatchParentChildren.get(i);            final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();            int childWidthMeasureSpec;            int childHeightMeasureSpec;                        if (lp.width == LayoutParams.MATCH_PARENT) {                childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() -                        getPaddingLeftWithForeground() - getPaddingRightWithForeground() -                        lp.leftMargin - lp.rightMargin,                        MeasureSpec.EXACTLY);            } else {                childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,                        getPaddingLeftWithForeground() + getPaddingRightWithForeground() +                        lp.leftMargin + lp.rightMargin,                        lp.width);            }                        if (lp.height == LayoutParams.MATCH_PARENT) {                childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() -                        getPaddingTopWithForeground() - getPaddingBottomWithForeground() -                        lp.topMargin - lp.bottomMargin,                        MeasureSpec.EXACTLY);            } else {                childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec,                        getPaddingTopWithForeground() + getPaddingBottomWithForeground() +                        lp.topMargin + lp.bottomMargin,                        lp.height);            }            child.measure(childWidthMeasureSpec, childHeightMeasureSpec);        }    }}

/** * {@inheritDoc} */@Overrideprotected void onLayout(boolean changed, int left, int top, int right, int bottom) {    layoutChildren(left, top, right, bottom, false /* no force left gravity */);}void layoutChildren(int left, int top, int right, int bottom,                              boolean forceLeftGravity) {    final int count = getChildCount();    final int parentLeft = getPaddingLeftWithForeground();    final int parentRight = right - left - getPaddingRightWithForeground();    final int parentTop = getPaddingTopWithForeground();    final int parentBottom = bottom - top - getPaddingBottomWithForeground();    mForegroundBoundsChanged = true;        for (int i = 0; i < count; i++) {        final View child = getChildAt(i);        if (child.getVisibility() != GONE) {            final LayoutParams lp = (LayoutParams) child.getLayoutParams();            final int width = child.getMeasuredWidth();            final int height = child.getMeasuredHeight();            int childLeft;            int childTop;            int gravity = lp.gravity;            if (gravity == -1) {                gravity = DEFAULT_CHILD_GRAVITY;            }            final int layoutDirection = getLayoutDirection();            final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);            final int verticalGravity = gravity & Gravity.VERTICAL_GRAVITY_MASK;            switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {                case Gravity.CENTER_HORIZONTAL:                    childLeft = parentLeft + (parentRight - parentLeft - width) / 2 +                    lp.leftMargin - lp.rightMargin;                    break;                case Gravity.RIGHT:                    if (!forceLeftGravity) {                        childLeft = parentRight - width - lp.rightMargin;                        break;                    }                case Gravity.LEFT:                default:                    childLeft = parentLeft + lp.leftMargin;            }            switch (verticalGravity) {                case Gravity.TOP:                    childTop = parentTop + lp.topMargin;                    break;                case Gravity.CENTER_VERTICAL:                    childTop = parentTop + (parentBottom - parentTop - height) / 2 +                    lp.topMargin - lp.bottomMargin;                    break;                case Gravity.BOTTOM:                    childTop = parentBottom - height - lp.bottomMargin;                    break;                default:                    childTop = parentTop + lp.topMargin;            }            child.layout(childLeft, childTop, childLeft + width, childTop + height);        }    }}

阅读全文

0 0