擷取View組件寬度以及ViewTreeObserver，

擷取View組件寬度以及ViewTreeObserver，
View寬高測量方法：

測量方法有三種，如下：

1）（直接在onCreate()執行）

int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);  int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);  imageView.measure(w, h);  int height =imageView.getMeasuredHeight();  int width =imageView.getMeasuredWidth();  textView.append("\n"+height+","+width);

2）2和3都是在onCreate()調用完後回調拿到組件的寬高

ViewTreeObserver vto = imageView.getViewTreeObserver();  vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {      public boolean onPreDraw() {          int height = imageView.getMeasuredHeight();          int width = imageView.getMeasuredWidth();          textView.append("\n"+height+","+width);          return true;      }  });

3）

ViewTreeObserver vto2 = imageView.getViewTreeObserver();    vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {      @Override        public void onGlobalLayout() {          imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);            textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());      }    });

注意：方法一比其他方法多一次onMeasure計算，方法二的回呼函數會被多次調用。