设置切换activity时显示的动画
Activity.overridePendingTransition();
public final boolean isAdded()
如果该Fragment对象被添加到了它的Activity中,那么它返回true,否则返回false。.
设置activity设置返回值:Activity.setResult,接收返回值Activity.onActivityResult()
appBar.addOnOffsetChangedListener(this)
handler.postDelayed(new Runnable() {})