获取View宽高的四种方式

  一开始写Android获取view的宽高的时候，经常会直接调用一些方法，实际获得的宽高都是0。后来才知道是因为View宽高的测量与Activity的生命周期并不是同步的，调用函数的时候很可能View的measure函数还没有执行完，下面介绍四种获取View宽高的方式。

1. onWindowFocusChanged

@Override
  public void onWindowFocusChanged(boolean hasFocus) {
    super.onWindowFocusChanged(hasFocus);
    if (hasFocus) {
      int width = view.getMeasuredWidth();
      int height = view.getMeasuredHeight();
    }
  }

2. view.post(runnable)

@Override
  protected void onStart() {
    super.onStart();
    view.post(new Runnable() {
      @Override
      public void run() {
        int width = view.getMeasuredWidth();
        int height = view.getMeasuredHeight();
      }
    });
  }

3. ViewTreeObserver

@Override
  protected void onStart() {
    super.onStart();
    ViewTreeObserver observer = view.getViewTreeObserver();
    observer.addOnGlobalLayoutListener(new OnGlobalLayoutListener(){
      @SuppressWarnings(value = "deprecation")
      @Override
      public void onGlobalLayout() {
        view.getViewTreeObserver().removeGlobalOnLayoutListener(this);
        int width = view.getMeasuredWidth();
        int height = view.getMeasuredHeight();
      }
    });
  }

4. view.measure(int widthMeasureSpec, int heightMeasureSpec)
   这种方法手动测量View的宽高，需要分三种情况:
    (1) View宽高为具体的值w, h

    int widthMeasureSpec = View.MeasureSpec.makeMeasureSpec(w, View.MeasureSpec.EXACTLY);
    int heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(h, View.MeasureSpec.EXACTLY);
    view.measure(widthMeasureSpec, heightMeasureSpec);

  (2) 设置为wrap_content

    int widthMeasureSpec =
        View.MeasureSpec.makeMeasureSpec(((1 << 30) - 1), View.MeasureSpec.AT_MOST);
    int heightMeasureSpec =
        View.MeasureSpec.makeMeasureSpec(((1 << 30) - 1), View.MeasureSpec.AT_MOST);
    view.measure(widthMeasureSpec, heightMeasureSpec);

  (3)设置为match_parent时是不能测出具体的宽高的，因为获取不到parentSize。