这个问题肯定经常出现。

当用户在Android应用程序中编辑首选项时,我希望他们能够在首选项摘要中看到当前设置的首选项值。

例如:如果我有“丢弃旧消息”的首选项设置,该设置指定了需要清理消息的天数。在PreferenceActivity中,我想让用户看到:

"丢弃旧消息" <- title

“x天后清理消息”<- summary,其中x是当前首选项值

额外的学分:使此可重用,所以我可以很容易地将它应用到我的所有首选项,而不管它们的类型(使它与EditTextPreference, ListPreference等工作,只需最少的编码)。


当前回答

我的选择是扩展ListPreference,它是干净的:

public class ListPreferenceShowSummary extends ListPreference {

    private final static String TAG = ListPreferenceShowSummary.class.getName();

    public ListPreferenceShowSummary(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public ListPreferenceShowSummary(Context context) {
        super(context);
        init();
    }

    private void init() {

        setOnPreferenceChangeListener(new OnPreferenceChangeListener() {

            @Override
            public boolean onPreferenceChange(Preference arg0, Object arg1) {
                arg0.setSummary(getEntry());
                return true;
            }
        });
    }

    @Override
    public CharSequence getSummary() {
        return super.getEntry();
    }
}

然后你添加你的settings.xml:

<yourpackage.ListPreferenceShowSummary
    android:key="key" android:title="title"
    android:entries="@array/entries" android:entryValues="@array/values"
    android:defaultValue="first value"/>

其他回答

EditTextPreference:

我来到这个解决方案,当然,只是如果你需要特定的edittextpreference,但你可以这样做,每一个偏好:

............

private static final String KEY_EDIT_TEXT_PREFERENCE2 = "on_a1";
public static  String value = "";

............

private void updatePreference(Preference preference, String key) {

            if (key.equals(KEY_EDIT_TEXT_PREFERENCE2)) {
                preference = findPreference(key);
                if (preference instanceof EditTextPreference) {
                    editTextPreference = (EditTextPreference) preference;
                    editTextPreference.setSummary(editTextPreference.getText());
                    value = editTextPreference.getText().toString();
                    return;
                }
                SharedPreferences sharedPrefs = getPreferenceManager().getSharedPreferences();
                preference.setSummary(sharedPrefs.getString(KEY_EDIT_TEXT_PREFERENCE2, ""));

            }
}

然后在onResume();

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

            SharedPreferences etext = getPreferenceManager().getSharedPreferences();
            String str = etext.getString("value", "");
            editTextPreference = (EditTextPreference) findPreference(KEY_EDIT_TEXT_PREFERENCE2);
            editTextPreference.setText(str);
            editTextPreference.setSummary(editTextPreference.getText());

            getPreferenceScreen().getSharedPreferences()
                    .registerOnSharedPreferenceChangeListener(this);
        }

In:

@Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            updatePreference(findPreference(key), key);
}

如果你正在使用AndroidX,你可以使用一个自定义的SummaryProvider。此方法可用于任何首选项。

来自文档的例子(Java):

EditTextPreference countingPreference = (EditTextPreference) findPreference("counting");

countingPreference.setSummaryProvider(new SummaryProvider<EditTextPreference>() {
    @Override
    public CharSequence provideSummary(EditTextPreference preference) {
        String text = preference.getText();
        if (TextUtils.isEmpty(text)){
            return "Not set";
        }
        return "Length of saved value: " + text.length();
    }
});

来自文档的例子(Kotlin):

val countingPreference = findPreference("counting") as EditTextPreference

countingPreference.summaryProvider = SummaryProvider<EditTextPreference> { preference ->
    val text = preference.text
    if (TextUtils.isEmpty(text)) {
        "Not set"
    } else {
        "Length of saved value: " + text.length
    }
}

因为我使用了一个自定义PreferenceDataStore,我不能添加一个监听器到一些SharedPreference,所以我不得不写一个有点hack的解决方案,监听每个偏好:

class SettingsFragment : PreferenceFragmentCompat(), Preference.OnPreferenceChangeListener {
    private val handler: Handler by lazy { Handler(Looper.getMainLooper()) }

    override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
        preferenceManager.preferenceDataStore = prefs
        addPreferencesFromResource(R.xml.app_preferences)
        onPreferenceChange(preferenceScreen, null)
    }

    override fun onPreferenceChange(preference: Preference, newValue: Any?): Boolean {
        preference.onPreferenceChangeListener = this

        when (preference) {
            is PreferenceGroup -> for (i in 0 until preference.preferenceCount) {
                onPreferenceChange(preference.getPreference(i), null)
            }
            is ListPreference -> {
                if (preference.value == null) {
                    preference.isPersistent = false
                    preference.value = Preference::class.java.getDeclaredField("mDefaultValue")
                            .apply { isAccessible = true }
                            .get(preference).toString()
                    preference.isPersistent = true
                }

                postPreferenceUpdate(Runnable { preference.summary = preference.entry })
            }
        }
        return true
    }

    /**
     * We can't directly update the preference summary update because [onPreferenceChange]'s result
     * is used to decide whether or not to update the pref value.
     */
    private fun postPreferenceUpdate(r: Runnable) = handler.post(r)
}

根据Android文档,你可以在ListPreference和EditTextPreference组件中使用app:useSimpleSummaryProvider="true"。

我发现这种方法使EditTextPreference从支持库句柄“%s”在总结(因为ListPreference已经处理):

public class EditTextPreference extends android.support.v7.preference.EditTextPreference {
    public EditTextPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void setText(String text) {
        super.setText(text);
        notifyChanged();
    }

    @Override
    public CharSequence getSummary() {
        String text = super.getText();
        String summary = super.getSummary().toString();
        return String.format(summary, text == null ? "" : text);
    }
}

在xml中它看起来是这样的:

<com.example.yourapp.EditTextPreference
    android:defaultValue="1"
    android:key="cleanup_period"
    android:summary="Clean up messages after %s days"
    android:title="Clean up period" />