来自savedInstanceState的数据在Android中始终为空

Question

我正在开发一款Android应用。我正在测试在活动中使用onSaveInstanceState事件。但它没有像我预期的那样工作，因为当我将它检索回onCreate事件时，值字符串总是为空的。

这是我的活动

@Override
    public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
        super.onSaveInstanceState(outState, outPersistentState);
        outState.putString("message","Hello world!");
    }

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if(savedInstanceState!=null)
    {
        Toast.makeText(getBaseContext(),savedInstanceState.getString("message"),Toast.LENGTH_SHORT).show();
        //Log.i("DATA_FROM_STATE",savedInstanceState.getString("message"));
    }
}

当我运行活动并改变方向时，它总是在烘烤空信息。当我测试取消注释日志行时，它给我错误，因为数据字符串为空或为空。为什么不工作？如何正确保存和检索？

Answer 1

错误的方法覆盖。应该使用onSaveInstanceState（Bundle outState），它会工作。您可以复制下面的代码段并进行测试。

public class MainActivity extends AppCompatActivity {

    private final String SAVED_MESSAGE_KEY = "SAVED_MESSAGE";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(savedInstanceState != null) {
            if(savedInstanceState.containsKey(SAVED_MESSAGE_KEY)) {
                Log.i("Saved message is:", savedInstanceState.getString(SAVED_MESSAGE_KEY));
            }
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString(SAVED_MESSAGE_KEY, "Hello world!");
    }
}

Answer 2

乍一看，我看到你在保存数据之前打电话给超级我想你的应用程序是在Android的API21 +版本上运行，因为需要调用你的方法

public void onSaveInstanceState (Bundle outState, PersistableBundle outPersistentState);

@Override
    public void onSaveInstanceState(Bundle outState,PersistableBundle outPersistentState) {
        outState.putString("message","Hello world!");
        super.onSaveInstanceState(outState, outPersistentState);

    }