请教关于FrameLayout的测量问题

2015-10-13 10:12:34 225 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

告别第三方应用！用Android原生API搭建Miracast投屏接收器本文深入探讨如何利用Android原生API开发Miracast接收器，绕过第三方依赖，实现高效的屏幕共享。通过Wi-Fi P2P直连、反射调用隐藏API和RTSP会话协商等核心技术，为开发者提供了一套完整的Miracast接收端解决方案，适用于多屏协同场景。阅读详情

刚看了下FrameLayout的测量onMeasure方法，代码比较少，比较容易看，但还是有些不明白，整个方法先遍历对每个View进行测量,并且如果FrameLayout布局参数不是match_parent的话，会记录所有布局参数为match_parent的子view,然后对这些子view再测量一次，就是第二次测量的这部分代码不明白

 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        int count = getChildCount();



        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) {

                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());

                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());

        }



        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),

                resolveSizeAndState(maxHeight, heightMeasureSpec,

                        childState << MEASURED_HEIGHT_STATE_SHIFT));



        count = mMatchParentChildren.size();

        if (count > 1) {

            for (int i = 0; i < count; i++) {

                final View child = mMatchParentChildren.get(i);



                final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

                int childWidthMeasureSpec;

                int childHeightMeasureSpec;

                

                if (lp.width == LayoutParams.MATCH_PARENT) {

//不明白的在这里，为何重新确定宽高，并且将已经确定的宽高减去padding和margin是什么意思

                    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);

                }



                child.measure(childWidthMeasureSpec, childHeightMeasureSpec);

            }

        }

    }