view 树的渲染过程

最新推荐文章于 2024-03-24 08:20:53 发布

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本文详细解析了MeasureSpec的创建及使用方式，并介绍了ViewRoot如何初始化MeasureSpec，随后深入探讨了DecorView的测量过程，包括其测量堆栈的具体实现。

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1，创建MeasureSpec

为32位的int数值，其中前面2位为mode，后面30位为size；

mode包含有exactly, at_most, unspecified;

 public static int makeMeasureSpec(int size, int mode) {
            if (sUseBrokenMakeMeasureSpec) {
                return size + mode;
            } else {
                return (size & ~MODE_MASK) | (mode & MODE_MASK);
            }

2, 初始化view root的spec

rootDimension根据创建window指定的attrs?

viewRoot

   private static int getRootMeasureSpec(int windowSize, int rootDimension) {
        int measureSpec;
        switch (rootDimension) {

        case ViewGroup.LayoutParams.MATCH_PARENT:
            // Window can't resize. Force root view to be windowSize.
            measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
            break;
        case ViewGroup.LayoutParams.WRAP_CONTENT:
            // Window can resize. Set max size for root view.
            measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
            break;
        default:
            // Window wants to be an exact size. Force root view to be that size.
            measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
            break;
        }
        return measureSpec;
    }

3, viewRoot

performTranversals -> measure layout draw

4, DecorView 树

RelativeLayout后面的为setcontentView之后的view树；

没有title的情况下：

5，DecroView Measure堆栈

LinearLayout(View).measure(int, int) line: 16471	
PhoneWindow$DecorView(ViewGroup).measureChildWithMargins(View, int, int, int, int) line: 5125	
PhoneWindow$DecorView(FrameLayout).onMeasure(int, int) line: 310	
PhoneWindow$DecorView.onMeasure(int, int) line: 2291       : super.onMeasure
PhoneWindow$DecorView(View).measure(int, int) line: 16497	
ViewRootImpl.performMeasure(int, int) line: 1916	
ViewRootImpl.measureHierarchy(View, WindowManager$LayoutParams, Resources, int, int) line: 1113	
ViewRootImpl.performTraversals() line: 1295