自定义控件(View的绘制流程源码解析)

1 childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
2                 childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
3                 performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);

 1 /**
 2      * Figures out the measure spec for the root view in a window based on it‘s
 3      * layout params.
 4      *
 5      * @param windowSize
 6      *            The available width or height of the window
 7      *
 8      * @param rootDimension
 9      *            The layout params for one dimension (width or height) of the
10      *            window.
11      *
12      * @return The measure spec to use to measure the root view.
13      */
14     private static int getRootMeasureSpec(int windowSize, int rootDimension) {
15         int measureSpec;
16         switch (rootDimension) {
17 
18         case ViewGroup.LayoutParams.MATCH_PARENT:
19             // Window can‘t resize. Force root view to be windowSize.
20             measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
21             break;
22         case ViewGroup.LayoutParams.WRAP_CONTENT:
23             // Window can resize. Set max size for root view.
24             measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
25             break;
26         default:
27             // Window wants to be an exact size. Force root view to be that size.
28             measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
29             break;
30         }
31         return measureSpec;
32     }