View的getWidth/getHeight与getMeasuredWidth/getMeasuredHeight的区别

某个View的显示流程是这样的：

Activity.onCreate-->Activity.onStart-->Activity.onResume-->image.onMeasure-->image.onLayout-->onGlobalLayoutListener-->Activity.onWindowFocusChanged-->....-->image.onDraw

onWindowFocusChanged是当activity可见时的调用的，在此之前的函数中调用View.getWidth/getHeight得到的是0，onWindowFocusChanged函数中获View.getWidth/getHeight是合适的。getWidth/getHeight一般是控件添加到Activity之后，显示到屏幕中的实际宽度。而View.getMeasureWidth/getMeasureHeight是配合view.measure使用的，如果未调用View.measure，那么调用view.getMeasureWidth的效果和View.getWidth一样。

如果我们要在onWindowFocusChanged之前的函数，如onCreate中获得View的宽度/高度，有如下三种方法：

方法一：

int width =View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
int height =View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
view.measure(width,height);
int height=view.getMeasuredHeight();
int width=view.getMeasuredWidth();

方法二：

//增加组件绘制之前的监听

ViewTreeObserver vto =view.getViewTreeObserver();
vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
   @Override
   public boolean onPreDraw() {
     int height =view.getMeasuredHeight();
     int width =view.getMeasuredWidth();
   }
});

方法三：

//增加整体布局监听

ViewTreeObserver vto = view.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener(){
    @Override
    public void onGlobalLayout() {
      view.getViewTreeObserver().removeGlobalOnLayoutListener(this);
      int height =view.getMeasuredHeight();
      int width =view.getMeasuredWidth();
    }
});