Android 獲取View寬高

一般情況：

View's getWidth() and getHeight() returns 0

View初始狀態爲GONE的情況

    private int mMeasuredHeight;
    private int mMeasuredWidth;

    private boolean firstVisible = true;

    @Override
    protected void onVisibilityChanged(@NonNull View changedView, int visibility) {
        super.onVisibilityChanged(changedView, visibility);
        if (visibility == View.VISIBLE) {//可見狀態
            if (firstVisible) {
                mSeekBar.getViewTreeObserver().addOnGlobalLayoutListener(new         
                                               ViewTreeObserver.OnGlobalLayoutListener() {
                    @Override
                    public void onGlobalLayout() {
                        mMeasuredWidth = mSeekBar.getMeasuredWidth();
                        mMeasuredHeight = mSeekBar.getMeasuredHeight();
                        Log.e("", "onGlobalLayout " + mMeasuredWidth + " " + 
                                                                         mMeasuredHeight);
                        mSeekBar.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                    }
                });
                firstVisible = false;
            }
        }
    }