ViewTreeObserver vto = mArrowUp.getViewTreeObserver(); 

        vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() { 

            @Override 

            public void onGlobalLayout() { 

                mArrowUp.getViewTreeObserver().removeGlobalOnLayoutListener(this); 

                Log.e("Width",Integer.toString(mArrowUp.getWidth())); 

            } 

        });   

摘自 欧阳天涵的专栏