1. View的layout方法

public void layout(int l, int t, int r, int b) {
    
    int oldL = mLeft;
    int oldT = mTop;
    int oldB = mBottom;
    int oldR = mRight;

    boolean changed = isLayoutModeOptical(mParent) ?
            setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);

    if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
        onLayout(changed, l, t, r, b);
        ...
    }
}

2. View的onLayout

没有实现

protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
}

3. TextView的onLayout

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    super.onLayout(changed, left, top, right, bottom);
    if (mDeferScroll >= 0) {
        int curs = mDeferScroll;
        mDeferScroll = -1;
        bringPointIntoView(Math.min(curs, mText.length()));
    }
}

4. LinearLayout的onLayout

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    if (mOrientation == VERTICAL) {
        layoutVertical(l, t, r, b);
    } else {
        layoutHorizontal(l, t, r, b);
    }
}

void layoutVertical(int left, int top, int right, int bottom) {
        
    final int count = getVirtualChildCount();
    for (int i = 0; i < count; i++) {
        final View child = getVirtualChildAt(i);
        if (child == null) {
            childTop += measureNullChild(i);
        } else if (child.getVisibility() != GONE) {
            final int childWidth = child.getMeasuredWidth();
            final int childHeight = child.getMeasuredHeight();
            
            final LinearLayout.LayoutParams lp =
                    (LinearLayout.LayoutParams) child.getLayoutParams();
            
            childTop += lp.topMargin;
            // 调用setChildFrame
            setChildFrame(child, childLeft, childTop + getLocationOffset(child),
                    childWidth, childHeight);
            // childTop逐渐增加
            childTop += childHeight + lp.bottomMargin + getNextLocationOffset(child);

            i += getChildrenSkipCount(child, i);
        }
    }
}

private void setChildFrame(View child, int left, int top, int width, int height) {        
    child.layout(left, top, left + width, top + height);
}