如何在PreferenceFragmentCompat中从Preferences子屏幕移回主屏幕

Question

我正在尝试使用PreferenceFragmentCompat实现设置屏幕。我的首选项xml有一个这样的首选项子屏幕:

preferences.xml

    <CheckBoxPreference
        android:defaultValue="false"
        android:key="@string/pref_sound_key"
        android:summary="@string/pref_sound_summary"
        android:title="@string/pref_sound_title" />
    <PreferenceScreen android:title="Inner Screen">
        <CheckBoxPreference
            android:defaultValue="true"
            android:key="@string/key_1"
            android:title="@string/title_1" />
        <CheckBoxPreference
            android:defaultValue="true"
            android:key="@string/key_1"
            android:title="@string/title_1" />
        <CheckBoxPreference
            android:defaultValue="true"
            android:key="@string/key_2"
            android:title="@string/title_2" />
        <CheckBoxPreference
            android:defaultValue="true"
            android:key="@string/key_3"
            android:title="@string/title_3" />
    </PreferenceScreen>
</PreferenceScreen>

首选项主界面

现在，在应用程序中，子屏幕不打开，直到我实现PreferenceFragmentCompat。在父activity中OnPreferenceStartScreenCallback接口，在PreferenceFragmentCompat文档中指定。

MainActivity.java

public boolean onPreferenceStartScreen(PreferenceFragmentCompat preferenceFragmentCompat,
 PreferenceScreen preferenceScreen) {    
    preferenceFragmentCompat.setPreferenceScreen(preferenceScreen);
    return true;
}

问题就在这里出现了。在实现接口时，子屏幕打开，但随后我无法找到移动回第一个屏幕的方法。

偏好Subscreen

按后退键将关闭应用程序。

我是否可以在应用程序栏上放一个返回箭头，这样按下它就会把主屏幕带回来?

Answer 1

通过使用setPreferenceScreen，您将根首选项屏幕设置为子首选项屏幕，这将阻止您拥有可导航的首选项屏幕层次结构。

我建议您将每个PreferenceScreen视为一个Fragment，并在导航到子屏幕时添加一个新的Fragment。

@Override
public boolean onPreferenceStartScreen(PreferenceFragmentCompat preferenceFragmentCompat,
                                       PreferenceScreen preferenceScreen) {
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    MyPreferenceFragment fragment = new MyPreferenceFragment();
    Bundle args = new Bundle();
    args.putString(PreferenceFragmentCompat.ARG_PREFERENCE_ROOT, preferenceScreen.getKey());
    fragment.setArguments(args);
    ft.add(R.id.fragment_container, fragment, preferenceScreen.getKey());
    ft.addToBackStack(preferenceScreen.getKey());
    ft.commit();
    return true;
}

MyPreferenceFragment

public class MyPreferenceFragment extends AppPreferenceFragment {
   public static final String FRAGMENT_TAG = "my_preference_fragment";
   public MyPreferenceFragment() {
   }
   @Override
   public void onCreatePreferences(Bundle bundle, String rootKey) {
       setPreferencesFromResource(R.xml.preferences, rootKey);
   }
}

AppPreferenceFragment

public abstract class AppPreferenceFragment extends PreferenceFragmentCompat {
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    // Set the default white background in the view so as to avoid transparency
      view.setBackgroundColor(
              ContextCompat.getColor(getContext(), R.color.background_material_light));
  }
}

这样，当你按下后退按钮时，每个Fragment将从堆栈中弹出。

更多信息请参见这个GitHub项目

Answer 2

我在这篇文章中添加了一个完整的工作示例，包括屏幕截图和代码片段，我希望这将对某人有所帮助。

它涵盖以下场景:——1)一个主设置屏幕，有两个复选框和一个子屏幕标题。2)点击子屏幕标题，新的首选项子屏幕打开。3)按下后，控制进入主设置界面。所以背压处理得当。

MainActivity看起来像这样(覆盖onPreferenceStartScreen方法处理在新窗口中打开新的子屏幕):——

  public class MainActivity extends AppCompatActivity implements PreferenceFragmentCompat.OnPreferenceStartScreenCallback {
    private static final String TAG = MainActivity.class.getName();
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FragmentManager fragmentManager = getSupportFragmentManager();
        Fragment fragment = null;
        if (savedInstanceState == null) {
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragment = new AdvancedSettingsFragment().newInstance("Advanced Setting");
            fragmentTransaction.add(R.id.fragment_container, fragment);
            fragmentTransaction.commit();
        }
    }
    @Override
        public boolean onPreferenceStartScreen(PreferenceFragmentCompat preferenceFragmentCompat,
                                           PreferenceScreen preferenceScreen) {
        Log.d(TAG, "callback called to attach the preference sub screen");
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        AdvancedSettingsSubScreenFragment fragment = AdvancedSettingsSubScreenFragment.newInstance("Advanced Settings Subscreen");
        Bundle args = new Bundle();
        //Defining the sub screen as new root for the  subscreen
        args.putString(PreferenceFragmentCompat.ARG_PREFERENCE_ROOT, preferenceScreen.getKey());
        fragment.setArguments(args);
        ft.replace(R.id.fragment_container, fragment, preferenceScreen.getKey());
        ft.addToBackStack(null);
        ft.commit();
        return true;
    }

，最后是in子屏幕片段setPreferencesFromResource(R.xml.preferences, rootKey);处理子屏幕到rootkey的附件

public class AdvancedSettingsSubScreenFragment extends PreferenceFragmentCompat {
    private static final String TAG = AdvancedSettingsSubScreenFragment.class.getName();
    public static final String PAGE_ID = "page_id";
    public static AdvancedSettingsSubScreenFragment newInstance(String pageId) {
        AdvancedSettingsSubScreenFragment f = new AdvancedSettingsSubScreenFragment();
        Bundle args = new Bundle();
        args.putString(PAGE_ID, pageId);
        f.setArguments(args);
        return (f);
    }
    @Override
    public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
        // rootKey is the name of preference sub screen key name , here--customPrefKey
        setPreferencesFromResource(R.xml.preferences, rootKey);
        Log.d(TAG, "onCreatePreferences of the sub screen " + rootKey);
    }
}