前言：今天在onCreate 的時候獲取view 的寬度 和 高度，發現結果是0。這就奇怪了，我已經在xml 中配置了高度、寬度了，怎麼會是0呢？度娘給出了答案！但是我還是希望能結合source code來解釋一下原因，所以我跟人小結一下。

首先呢，看一下我試驗的code：

    private void init() {
        int width = mTestView.getWidth();
        int height = mTestView.getHeight();
        Log.d(TAG, "====width =" + width + ", ====height =" + height);
        
        WindowManager wm = this.getWindowManager();
        int window_width = wm.getDefaultDisplay().getWidth();
        int window_height = wm.getDefaultDisplay().getHeight();
        Log.d(TAG, "====window_width =" + window_width + ", ====window_height =" + window_height);
    }
 

D/MainActivity( 2272): ====width =0, ====height =0

改一下：

    private void init() {
        mTestView.measure(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        int width = mTestView.getMeasuredWidth();
        int height = mTestView.getMeasuredHeight();
        Log.d(TAG, "====width =" + width + ", ====height =" + height);
        
        WindowManager wm = this.getWindowManager();
        int window_width = wm.getDefaultDisplay().getWidth();
        int window_height = wm.getDefaultDisplay().getHeight();
        Log.d(TAG, "====window_width =" + window_width + ", ====window_height =" + window_height);
    }
 

D/MainActivity( 2386): ====width =157, ====height =41

通過code，可以看出是主動呼叫了measure 的方法做了一次測量，相當於在原基礎上多了一次測量，好處就是可以立即獲取寬度和高度。

下面來具體總結一下其他方式；
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：

//增加元件繪製之前的監聽
ViewTreeObserver vto =view.getViewTreeObserver();
vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    @Override
    public boolean onPreDraw() {
        int height =view.getMeasuredHeight();
        int width =view.getMeasuredWidth();
    }
});

方法三：

//增加整體佈局監聽
ViewTreeObserver vto = view.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener(){
    @Override
    public void onGlobalLayout() {
        view.getViewTreeObserver().removeGlobalOnLayoutListener(this);
        int height =view.getMeasuredHeight();
        int width =view.getMeasuredWidth();
    }
});