前言：代码很简单，网上资料很多，此篇只是做记录用。

1. ViewTreeObserver

ViewTreeObserver vto = mRootView.getViewTreeObserver();
        vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                    mRootView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                } else {
                    mRootView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
                }
                mRootView.getHeight();
                mRootView.getWidth();
            }
        });

2. View.post(new Runnable())

mRootView.post(new Runnable() {
            @Override
            public void run() {
                mRootView.getWidth();
                mRootView.getHeight();
            }
        });