View -＞ 测量宽高measuredWidth、measuredHeight和布局宽高width、height的区别

测量宽高measuredWidth、measuredHeight

View的measuredWidth、measuredHeight如何赋值的？

ViewRootImpl.scheduleTraversals()->测量、布局和绘制过程的起点
ViewRootImpl.doTraversal()->
ViewRootImpl.performTraversals()->

• ViewRootImpl.performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec)->传入父View给到子View的MeasureSpec测量规格，包括大小和模式
  • View.measure(int widthMeasureSpec, int heightMeasureSpec)->
  • View.onMeasure(int widthMeasureSpec, int heightMeasureSpec)->
  • View.getDefaultSize(int size, int measureSpec)：根据MeasureSpec测量规格计算子View的measuredWidth、measuredHeight
  • View.setMeasuredDimension(int measuredWidth, int measuredHeight)->
  • View.setMeasuredDimensionRaw(measuredWidth, measuredHeight)：记录measuredWidth、measuredHeight

public static int getDefaultSize(int size, int measureSpec) {
    int result = size;
    int specMode = MeasureSpec.getMode(measureSpec);
    int specSize = MeasureSpec.getSize(measureSpec);

    switch (specMode) {
    case MeasureSpec.UNSPECIFIED:
        result = size;
        break;
    case MeasureSpec.AT_MOST:
    case MeasureSpec.EXACTLY:
        result = specSize;
        break;
    }
    return result;
}

private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
    mMeasuredWidth = measuredWidth;
    mMeasuredHeight = measuredHeight;

    mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
}

布局宽高width、height

View的width、height如何赋值的？

ViewRootImpl.scheduleTraversals()->测量、布局和绘制过程的起点
ViewRootImpl.doTraversal()->
ViewRootImpl.performTraversals()->

• ViewRootImpl.performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth, int desiredWindowHeight)：WindowManager.LayoutParams 提供窗口的详细配置，而 desiredWindowWidth 和 desiredWindowHeight 则提供目标View尺寸，最终决定View的布局和显示
  • View.layout(int l, int t, int r, int b)->
  • View.setFrame(int left, int top, int right, int bottom)->记录mLeft、mTop、mRight、mBottom，其中width=mRight-mLeft，height=mBottom-mTop，计算出View的布局宽高width、height

protected boolean setFrame(int left, int top, int right, int bottom) {
    ...
	mLeft = left;
	mTop = top;
	mRight = right;
	mBottom = bottom;
    ...
}

测量宽高measuredWidth、measuredHeight和布局宽高width、height

• 应用场景
  • getMeasuredWidth() / getMeasuredHeight()：在onLayout()中获取View的宽/高
  • getWidth() / getHeight()：在除onLayout()外的地方获取View的宽/高
• 关系：
  • 不去layout方法中去修改left, top, right, bottom，getWidth() / getHeight()获得的宽高（View的布局宽高）与 getMeasuredWidth() / getMeasuredHeight()获得的宽高（View的测量宽高 ）永远是相等的