FrameLayout 測量過程（程式碼流水線）
阿新 • • 發佈：2019-02-03
/**
* {@inheritDoc}
* 如果，子 view如果設定屬性是 match_parent，
* 如果，measureMatchParentChildren是true (其實就是framlayout模式是非精準模式)
* 那麼這種子view是被測量了兩次
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int count = getChildCount();
//當FrameLayout的寬和高 只有同時設定為 match_parent protected void measureChildWithMargins(View child,
int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
//根據parentWidthMeasureSpec，ViewGroup剩餘寬度，child的寬度重新計算child的widthMeasureSpec
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
+ widthUsed, lp.width);
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
+ heightUsed, lp.height);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
/**
* @param spec The requirements for this view
* parentHeightMeasureSpec
* @param padding The padding of this view for the current dimension and
* margins, if applicable
* 父親已經用的 + 父親的pading + 父親的margin
* @param childDimension How big the child wants to be in the current
* dimension
* @return a MeasureSpec integer for the child
* 孩子的佈局引數
*/
public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
//得到父親的測量模式和大小
int specMode = MeasureSpec.getMode(spec);
int specSize = MeasureSpec.getSize(spec);
//父親大小 - 父親的冗餘
//當前父View還剩的空間大小
int size = Math.max(0, specSize - padding);
int resultSize = 0;
int resultMode = 0;
switch (specMode) {
// Parent has imposed an exact size on us
case MeasureSpec.EXACTLY:// 父View強制設定了一個大小給子View
if (childDimension >= 0) {//大小就是 孩子引數的大小
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.MATCH_PARENT) {//大小就是 父親剩餘空間的大小
// Child wants to be our size. So be it.
resultSize = size;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {//大小設定為父親剩餘空間大小，意味著讓子View去處理，子View最大的大小不能超過父View
// Child wants to determine its own size. It can't be
// bigger than us.
resultSize = size;
resultMode = MeasureSpec.AT_MOST;
}
break;
// Parent has imposed a maximum size on us
case MeasureSpec.AT_MOST:// 父View給子View一個限定的大小，子View不能超過這個大小
if (childDimension >= 0) {// 子View的size設定成XML中配置的大小
// Child wants a specific size... so be it
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.MATCH_PARENT) {// 子View的大小為父View的size 意味著讓子View去處理，子View最大的大小不能超過父View
// Child wants to be our size, but our size is not fixed.
// Constrain child to not be bigger than us.
resultSize = size;
resultMode = MeasureSpec.AT_MOST;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {//同上
// Child wants to determine its own size. It can't be
// bigger than us.
resultSize = size;
resultMode = MeasureSpec.AT_MOST;
}
break;
// Parent asked to see how big we want to be
case MeasureSpec.UNSPECIFIED:// 意味著子View要多大都可以
if (childDimension >= 0) {//子View的size設定成XML中配置的大小
// Child wants a specific size... let him have it
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;//意味著，我可以給讓你想顯示多大就顯示多大，但是在XML中或者addView的時候， 寫死了childDimension，那麼它的大小就這麼大吧
} else if (childDimension == LayoutParams.MATCH_PARENT) {//意味著大小讓它自己決定到底要多大，隨便多大都可以
// Child wants to be our size... find out how big it should
// be
resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
resultMode = MeasureSpec.UNSPECIFIED;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {// 意味著大小讓它自己決定到底要多大，隨便多大都可以
// Child wants to determine its own size.... find out how
// big it should be
resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
resultMode = MeasureSpec.UNSPECIFIED;
}
break;
}
return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
}