FrameLayout布局使用问题（一）

在一次使用FrameLayout的时候，FrameLayout大小是自适应，其中一个子视图的宽高都是match_parent，也就是由FrameLayout的最终大小决定，结果出现了子视图大小取了默认值的情况，这就很是纳闷了

"match_parent"
        android:layout_height="wrap_content">

        <com.csw.fragmenttest.imageloopplayer.DotIndicate
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#AA000000" />

        "wrap_content"
            android:layout_height="60dp"
            android:gravity="center"
            android:text="测试文本" />

    

通过对自定义视图测量方法打断点，发现高度的模式是AT_MOST。。。
研究FrameLayout的源码，发现FrameLayout测量方法有点诡异。

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int count = getChildCount();
        //如果FrameLayout宽高有不是精确值的，需要再测量一次match_parent的子视图
        final boolean measureMatchParentChildren =
                MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.EXACTLY ||
                MeasureSpec.getMode(heightMeasureSpec) != MeasureSpec.EXACTLY;
        mMatchParentChildren.clear();

        int maxHeight = 0;
        int maxWidth = 0;
        int childState = 0;

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (mMeasureAllChildren || child.getVisibility() != GONE) {
                //测量子视图，记录最大宽高，不多说
                measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
                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());
                //如果需要测量match_parent宽或高的子视图，将match_parent子视图添加到集合
                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());
        }
        //完成测量
        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
                resolveSizeAndState(maxHeight, heightMeasureSpec,
                        childState << MEASURED_HEIGHT_STATE_SHIFT));
        //读取需要再测量的子视图数量
        count = mMatchParentChildren.size();
        //如果数量大于1？？？
        if (count > 1) {
            for (int i = 0; i < count; i++) {
                final View child = mMatchParentChildren.get(i);
                final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

                final int childWidthMeasureSpec;
                //如果是match_parent,测量子视图时使用精确模式+可用宽度
                //下面的高度也是差不多
                if (lp.width == LayoutParams.MATCH_PARENT) {
                    final int width = Math.max(0, getMeasuredWidth()
                            - getPaddingLeftWithForeground() - getPaddingRightWithForeground()
                            - lp.leftMargin - lp.rightMargin);
                    childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
                            width, MeasureSpec.EXACTLY);
                } else {
                    childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
                            getPaddingLeftWithForeground() + getPaddingRightWithForeground() +
                            lp.leftMargin + lp.rightMargin,
                            lp.width);
                }

                final int childHeightMeasureSpec;
                if (lp.height == LayoutParams.MATCH_PARENT) {
                    final int height = Math.max(0, getMeasuredHeight()
                            - getPaddingTopWithForeground() - getPaddingBottomWithForeground()
                            - lp.topMargin - lp.bottomMargin);
                    childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
                            height, MeasureSpec.EXACTLY);
                } else {
                    childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec,
                            getPaddingTopWithForeground() + getPaddingBottomWithForeground() +
                            lp.topMargin + lp.bottomMargin,
                            lp.height);
                }

                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
            }
        }
    }

如以上代码所展示，不知为何要match_parent属性的子视图多于一个才会再去测量一次，只有一个子视图时match_parent时子视图就可以无视吗。。。

解决方法：
1、多加一个match_parent的子视图，凑足>1。。。。
2、如上面的实例布局，修改一下另一个视图的布局参数，修改高度也为match_parent（也是凑足>1）,然后设置最小高度，这样他在第一次AT_MOST的测量中就会计算出60dp的测量高度

"match_parent"
        android:layout_height="wrap_content">

        <com.csw.fragmenttest.imageloopplayer.DotIndicate
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#AA000000" />

        "wrap_content"
            android:layout_height="match_parent"
            android:minHeight="60dp"
            android:gravity="center"
            android:text="测试文本" />