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/**
* {@inheritDoc}
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int count = getChildCount();
final boolean measureMatchParentChildren =
MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.EXACTLY ||
MeasureSpec.getMode(heightMeasureSpec) != MeasureSpec.EXACTLY;
//当FrameLayout的宽和高，只有同时设置为match_parent或者指定的size，那么这个
//measureMatchParentChlidren = false，否则为true。下面会用到这个变量
mMatchParentChildren.clear();
int maxHeight = 0;
int maxWidth = 0;
int childState = 0; //宽高的期望类型
for (int i = 0; i < count; i++) { //一次遍历每一个不为GONE的子view
final View child = getChildAt(i);
if (mMeasureAllChildren || child.getVisibility() != GONE) {
//去掉FrameLayout的左右padding，子view的左右margin，这时候，再去
//计算子view的期望的值
measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
/*maxWidth找到子View中最大的宽，高同理，为什么要找到他，因为在这里，FrameLayout是wrap
-content.他的宽高肯定受子view的影响*/
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());
/*下面的判断，只有上面的FragLayout的width和height都设置为match_parent 才不会执行
此处的mMatchParentChlidren的list里存的是设置为match_parent的子view。
结合上面两句话的意思，当FrameLayout设置为wrap_content，这时候要把所有宽高设置为
match_parent的子View都记录下来，记录下来干什么呢？
这时候FrameLayout的宽高同时受子View的影响*/
if (measureMatchParentChildren) {
if (lp.width == LayoutParams.MATCH_PARENT ||
lp.height == LayoutParams.MATCH_PARENT) {
mMatchParentChildren.add(child);
}
}
}
}
// 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());
}
//设置测量过的宽高
setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
resolveSizeAndState(maxHeight, heightMeasureSpec,
childState << MEASURED_HEIGHT_STATE_SHIFT));
count = mMatchParentChildren.size();//这个大小就是子view中设定为match_parent的个数
if (count > 1) {
for (int i = 0; i < count; i++) {
//这里看上去重新计算了一遍
final View child = mMatchParentChildren.get(i);
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
int childWidthMeasureSpec;
int childHeightMeasureSpec;
/*如果子view的宽是match_parent，则宽度期望值是总宽度-padding-margin
如果子view的宽是指定的比如100dp，则宽度期望值是padding+margin+width
这个很容易理解,下面的高同理*/
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);
}
//把这部分子view重新计算大小
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
}
}
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原文地址：http://my.oschina.net/u/1777377/blog/415845
