Question

我有一个设置Activity / Fragment，其中包含3个首选项，这些首选项是从首选项XML文件加载的。当我点击其中一个偏好时，它会启动一项新活动来发现蓝牙设备。我希望能够从此活动中选择蓝牙设备并将其作为首选项（MAC地址）保存。问题是我将设备保存在DiscoverBluetooth活动中并验证它是否存在，但在返回原始设置活动时，首选项仍为空。

DiscoverBluetooth列表活动：

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
    mEditor = prefs.edit();

    String macAddress = mArrayAdapter.getItem(position).split("\n")[1];
    if (D) Log.i(TAG, "Saving saved device with MAC address: " + macAddress);
    mEditor.putString(SettingsActivity.PrefsFragment.KEY_SAVED_DEVICE, macAddress).commit();
    if (D) Log.i(TAG, "saved device is now: " + prefs.getString(SettingsActivity.PrefsFragment.KEY_SAVED_DEVICE, "Invalid MAC"));

    finish();
}

设置活动片段：

public static class PrefsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener{
    public static final String KEY_END_CHARACTER = "list_endcharacter"; 
    public final static int DEFAULT_END_CHARACTER = R.string.preferences_list_endcharacter_default;
    public static final String KEY_DEVICE_UUID = "edittext_deviceuuid";
    public final static int DEFAULT_UUID = R.string.preferences_default_deviceuuid;
    public static final String KEY_SAVED_DEVICE = "edittext_saved_device";

    public static final char[] END_CHARACTER_VALUES = {'\n', '\r'};

    //Preference UI references
    private EditTextPreference savedDevicePref;
    private EditTextPreference deviceUuid;
    private ListPreference endCharacter;

    @Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        //load the preferences from an xml resource
        addPreferencesFromResource(R.xml.preferences);
        getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);


    }

    @Override
    public void onResume(){
        super.onResume();

        deviceUuid = (EditTextPreference) findPreference(KEY_DEVICE_UUID);
        savedDevicePref = (EditTextPreference) findPreference(KEY_SAVED_DEVICE);
        endCharacter = (ListPreference) findPreference(KEY_END_CHARACTER);

        updateEditTextSummary(deviceUuid);              
        updateListSummary(endCharacter);                

        if (savedDevicePref != null){
            updateEditTextSummary(savedDevicePref);
        } else {
            if (D) Log.i(TAG, "saved device pref is null");
        }
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
        if (key.equals(KEY_DEVICE_UUID)){
            updateEditTextSummary(deviceUuid);
        } else if (key.equals(KEY_END_CHARACTER)){
            updateListSummary(endCharacter);
        } else if (key.equals(KEY_SAVED_DEVICE)){
            Log.i(TAG,"New saved device: " + sharedPreferences.getString(key, null));
        }
    }

    private void updateListSummary(ListPreference lPreference){
        String summary = "";
        final CharSequence[] entries = lPreference.getEntries();
        if (entries == null || entries.length == 0){
            summary = "";
        } else{
            summary = lPreference.getEntry().toString();
        }

        lPreference.setSummary(summary);
    }

    private void updateEditTextSummary(EditTextPreference etPreference){
        String text = etPreference.getText();
        etPreference.setSummary(text);
    }
}

首选项XML

<?xml version="1.0" encoding="utf-8"?>

<PreferenceCategory
    android:title="@string/bluetooth_preferences">

    <ListPreference
        android:key="list_endcharacter"
        android:title="@string/preferences_title_endcharacter"
        android:entries="@array/preferences_list_endcharacter_strings"
        android:entryValues="@array/preferences_list_endcharacter"
        android:defaultValue="@string/preferences_list_endcharacter_default"/>

    <Preference
        android:title="@string/preferences_title_lastdevice"
        android:defaultValue="@string/preferences_default_saved_device">
        <intent 
            android:targetClass="com.robert_stuart.bluetoothtest.DiscoverBluetooth"
            android:targetPackage="com.robert_stuart.bluetoothtest"/>

    </Preference>

    <EditTextPreference
        android:key="edittext_deviceuuid"
        android:title="@string/preferences_title_deviceuuid"
        android:dialogTitle="@string/preferences_title_deviceuuid"
        android:defaultValue="@string/preferences_default_deviceuuid"/>

</PreferenceCategory>

选择MAC地址后记录输出

05-27 09:36:03.139: I/DiscoverBluetooth(2834): Saving saved device with MAC address: 00:14:03:02:13:49
05-27 09:36:03.139: I/DiscoverBluetooth(2834): saved device is now: 00:14:03:02:13:49
05-27 09:36:03.156: I/SettingsActivity(2834): saved device pref is null

知道这里发生了什么吗？谢谢你的帮助。

Answer 1

只是想确保在保存数据时在sharedPreference上调用commit（）。你能核实一下吗？

Answer 2

我意识到我从来没有为XML文件中的首选项定义一个键，所以即使我正确地保存了键，片段也指向什么，因此仍然为空。

<Preference
    android:title="@string/preferences_title_lastdevice"
    android:key="edittext_saved_device"
    android:defaultValue="@string/preferences_default_saved_device">
    <intent 
        android:targetClass="com.robert_stuart.bluetoothtest.DiscoverBluetooth"
        android:targetPackage="com.robert_stuart.bluetoothtest"/>

</Preference>

无法从子设置活动中保存共享首选项

2 个答案: