本文共 1875 字，大约阅读时间需要 6 分钟。

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);            }

rootDimension根据创建window指定的attrs?

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$DecorView.onMeasure(int, int) line: 2291       : super.onMeasurePhoneWindow$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