private String data="some user data";
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(savedInstanceState!=null) {//如果有数据被需恢复，onRestoreInstanceState会被触发，并将savedInstanceState传递到onCreate
            Log.d(TAG,"onRestoreInstanceState is not null...");
            data=savedInstanceState.getString("data");
        }
        
        //tv.setText(data);
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outdate.putString("data", data);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {//savedInstanceState会传递到onCreate，在onCreate中恢复
        super.onRestoreInstanceState(savedInstanceState);
        //data=savedInstanceState.getString("data");//不在这里用data=savedInstanceState.getString("data");直接来恢复。
    }