使用 'onStart' 方法时如何声明 savedInstanceState

Question

是否可以在我的片段的 onStart 方法中使用 if (savedInstanceState == null) {...}？每当我在 onCreate 方法中使用它时，我的片段都会显示为空白。

public class MyActivity extends AppCompatActivity {
    private static final String TAG = MyActivity.class.getSimpleName();

    private Boolean mCurrentValue;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.d(TAG, "onCreate:::: retrieving preferences");
        SharedPreferences mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        mCurrentValue = mSharedPreferences.getBoolean("my_preference", false);
        Log.d(TAG, "onCreate:::: my_preference and mCurrentValue=" + mCurrentValue);
        if (mCurrentValue) {
            setTheme(R.style.MyDarkAppCompatTheme);
            Log.d(TAG, "onCreate:::: setTheme:MyDarkAppCompatNoActionBarTheme");
        } else {
            setTheme(R.style.MyLightTheme);
            Log.d(TAG, "onCreate:::: setTheme:MyLightAppCompatNoActionBarTheme");
        }

        super.onCreate(savedInstanceState);

        setContentView(R.layout.my_activity);

        if (savedInstanceState == null) {

        }
    }


    // in order to recreate Activity we must check value here because when we come back from another Activity onCreate doesn't called again
    @Override
    protected void onStart() {
        super.onStart();

        setContentView(R.layout.my_activity);

        SharedPreferences mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        Boolean mNewValue = mSharedPreferences.getBoolean("my_preference", false);
        // if value differs from previous Theme, we recreate Activity
        if(mCurrentValue != mNewValue){
            recreate();
        }

        MyFragment newFragment = new MyFragment();
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.detail_container, newFragment);
        transaction.commit();
    }
}

Answer 1

没有。如果您需要访问保存的数据片段，您需要从 onCreate 中的 savedInstanceState Bundle 中提取它们并将它们保存为 Activity 中的字段。如果您只需要检测此 Activity 是否被重新创建（通常检查 savedInstanceState 是否为空），您可以在 Activity 中声明一个布尔字段，并在 savedInstanceState 为 null 时在 onCreate 中设置它在范围内，然后在 onStart 中访问它：

private boolean activityRecreated;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    activityRecreated = savedInstanceState != null;
}

@Override
public void onStart() {
    if (activityRecreated) {
       // code here
    }
}

编辑：在获得有关您尝试保存的状态的更多信息后，试试这个：您应该在 Activity 中有一个字段来跟踪 ViewPager 的状态。此标签保存用户所在的选项卡。它可以是 String 标签或 Id (int) 标签。您应该通过覆盖 Activity:

中的 onSaveInstanceState 来保存它

private int tabIndex = 0 // NOTE: get this from your ViewPager's PagerAdapter
@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt("tabIndex", tabIndex)
}

然后，在 onCreate 中，您可以检索此值：

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState != null) {
      tabIndex = savedInstanceState.getInt("tabIndex", 0);
      // here, make sure your ViewPager's PagerAdapter is created and set it to this tab
    }
    // rest of your onCreate goes here
}

以这种方式保存选项卡索引将允许 activity 重新创建正确的 ViewPager 选项卡可见。

使用 'onStart' 方法时如何声明 savedInstanceState

How to declare savedInstanceState when using 'onStart' method

java

android

android-preferences

android-activity