谢谢你的建议!

我有一个首选项屏幕，并希望显示每个列表首选项的值作为摘要。

这就是我现在的方式:

public class Preferences extends PreferenceActivity implements OnSharedPreferenceChangeListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);
}

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

    // Set up initial values for all list preferences
    Map<String, ?> sharedPreferencesMap = getPreferenceScreen().getSharedPreferences().getAll();
    Preference pref;
    ListPreference listPref;
    for (Map.Entry<String, ?> entry : sharedPreferencesMap.entrySet()) {
        pref = findPreference(entry.getKey());
        if (pref instanceof ListPreference) {
            listPref = (ListPreference) pref;
            pref.setSummary(listPref.getEntry());
        }
    }

    // Set up a listener whenever a key changes            
    getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
}

@Override
protected void onPause() {
    super.onPause();

    // Unregister the listener whenever a key changes            
    getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);    
}

public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
    Preference pref = findPreference(key);

    if (pref instanceof ListPreference) {
        ListPreference listPref = (ListPreference) pref;
        pref.setSummary(listPref.getEntry());
    }
}

这对我来说是可行的，但我想知道最好的解决方案(性能、稳定性、可伸缩性)是Koem展示的那个还是这个?

在我花了几个小时来解决这样的问题后，我实现了以下代码:

[更新:最终版本列表]

public class MyPreferencesActivity extends PreferenceActivity {
    ...
    ListPreference m_updateList;
    ...
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);

        m_updateList = (ListPreference) findPreference(getString(R.string.pref_update_interval_key));
        String currentValue = m_updateList.getValue();
        if (currentValue == null) {
            m_updateList.setValue((String)m_updateList.getEntryValues()[DEFAULT_UPDATE_TIME_INDEX]);
            currentValue = m_updateList.getValue();
        }
        updateListSummary(currentValue);    

        m_updateList.setOnPreferenceChangeListener(new OnPreferenceChangeListener() {
            @Override
            public boolean onPreferenceChange(Preference preference, Object newValue) {
                updateListSummary(newValue.toString());
                return true;
            }       
        });     
    }

    private void updateListSummary(String newValue) {
        int index = m_updateList.findIndexOfValue(newValue);
        CharSequence entry = m_updateList.getEntries()[index];
        m_updateList.setSummary(entry);
    }
}

这是唯一对我有效的解决方法。在我尝试子类从ListPreferences和实现android:summary="bla bla bla %s"。既不工作。

由于在androidx首选项类有SummaryProvider接口，它可以在没有OnSharedPreferenceChangeListener的情况下完成。为EditTextPreference和ListPreference提供了简单的实现。根据EddieB的答案，它看起来像这样。在androidx.preference上测试:preference:1.1.0-alpha03。

package com.example.util.timereminder.ui.prefs;

import android.os.Bundle;

import com.example.util.timereminder.R;

import androidx.preference.EditTextPreference;
import androidx.preference.ListPreference;
import androidx.preference.Preference;
import androidx.preference.PreferenceFragmentCompat;
import androidx.preference.PreferenceGroup;

/**
 * Displays different preferences.
 */
public class PrefsFragmentExample extends PreferenceFragmentCompat {

    @Override
    public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
        addPreferencesFromResource(R.xml.preferences);

        initSummary(getPreferenceScreen());
    }

    /**
     * Walks through all preferences.
     *
     * @param p The starting preference to search from.
     */
    private void initSummary(Preference p) {
        if (p instanceof PreferenceGroup) {
            PreferenceGroup pGrp = (PreferenceGroup) p;
            for (int i = 0; i < pGrp.getPreferenceCount(); i++) {
                initSummary(pGrp.getPreference(i));
            }
        } else {
            setPreferenceSummary(p);
        }
    }

    /**
     * Sets up summary providers for the preferences.
     *
     * @param p The preference to set up summary provider.
     */
    private void setPreferenceSummary(Preference p) {
        // No need to set up preference summaries for checkbox preferences because
        // they can be set up in xml using summaryOff and summary On
        if (p instanceof ListPreference) {
            p.setSummaryProvider(ListPreference.SimpleSummaryProvider.getInstance());
        } else if (p instanceof EditTextPreference) {
            p.setSummaryProvider(EditTextPreference.SimpleSummaryProvider.getInstance());
        }
    }
}

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);
}

Here,all these are cut from Eclipse sample SettingsActivity. I have to copy all these too much codes to show how these android developers choose perfectly for more generalized and stable coding style. I left the codes for adapting the PreferenceActivity to tablet and greater API. public class SettingsActivity extends PreferenceActivity { @Override protected void onPostCreate(Bundle savedInstanceState) { super.onPostCreate(savedInstanceState); setupSummaryUpdatablePreferencesScreen(); } private void setupSummaryUpdatablePreferencesScreen() { // In the simplified UI, fragments are not used at all and we instead // use the older PreferenceActivity APIs. // Add 'general' preferences. addPreferencesFromResource(R.xml.pref_general); // Bind the summaries of EditText/List/Dialog preferences to // their values. When their values change, their summaries are updated // to reflect the new value, per the Android Design guidelines. bindPreferenceSummaryToValue(findPreference("example_text")); bindPreferenceSummaryToValue(findPreference("example_list")); } /** * A preference value change listener that updates the preference's summary * to reflect its new value. */ private static Preference.OnPreferenceChangeListener sBindPreferenceSummaryToValueListener = new Preference.OnPreferenceChangeListener() { private String TAG = SettingsActivity.class.getSimpleName(); @Override public boolean onPreferenceChange(Preference preference, Object value) { String stringValue = value.toString(); if (preference instanceof ListPreference) { // For list preferences, look up the correct display value in // the preference's 'entries' list. ListPreference listPreference = (ListPreference) preference; int index = listPreference.findIndexOfValue(stringValue); // Set the summary to reflect the new value. preference.setSummary( index >= 0 ? listPreference.getEntries()[index] : null); } else { // For all other preferences, set the summary to the value's // simple string representation. preference.setSummary(stringValue); } Log.i(TAG, "pref changed : " + preference.getKey() + " " + value); return true; } }; /** * Binds a preference's summary to its value. More specifically, when the * preference's value is changed, its summary (line of text below the * preference title) is updated to reflect the value. The summary is also * immediately updated upon calling this method. The exact display format is * dependent on the type of preference. * * @see #sBindPreferenceSummaryToValueListener */ private static void bindPreferenceSummaryToValue(Preference preference) { // Set the listener to watch for value changes. preference.setOnPreferenceChangeListener(sBindPreferenceSummaryToValueListener); // Trigger the listener immediately with the preference's // current value. sBindPreferenceSummaryToValueListener.onPreferenceChange(preference, PreferenceManager .getDefaultSharedPreferences(preference.getContext()) .getString(preference.getKey(), "")); } } xml/pref_general.xml <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" > <!-- NOTE: EditTextPreference accepts EditText attributes. --> <!-- NOTE: EditTextPreference's summary should be set to its value by the activity code. --> <EditTextPreference android:capitalize="words" android:defaultValue="@string/pref_default_display_name" android:inputType="textCapWords" android:key="example_text" android:maxLines="1" android:selectAllOnFocus="true" android:singleLine="true" android:title="@string/pref_title_display_name" /> <!-- NOTE: Hide buttons to simplify the UI. Users can touch outside the dialog todismiss it.--> <!-- NOTE: ListPreference's summary should be set to its value by the activity code. --> <ListPreference android:defaultValue="-1" android:entries="@array/pref_example_list_titles" android:entryValues="@array/pref_example_list_values" android:key="example_list" android:negativeButtonText="@null" android:positiveButtonText="@null" android:title="@string/pref_title_add_friends_to_messages" /> </PreferenceScreen> values/strings_activity_settings.xml <resources> <!-- Strings related to Settings --> <!-- Example General settings --> <string name="pref_title_display_name">Display name</string> <string name="pref_default_display_name">John Smith</string> <string name="pref_title_add_friends_to_messages">Add friends to messages</string> <string-array name="pref_example_list_titles"> <item>Always</item> <item>When possible</item> <item>Never</item> </string-array> <string-array name="pref_example_list_values"> <item>1</item> <item>0</item> <item>-1</item> </string-array> </resources> NOTE: Actually I just want to comment like "Google's sample for PreferenceActivity is also interesting". But I haven't enough reputation points.So please don't blame me. (Sorry for bad English)

在Android Studio中，打开“root_preferences.xml”，选择设计模式。选择所需的EditTextPreference首选项，在“所有属性”下，寻找“useSimpleSummaryProvider”属性，并将其设置为true。然后它将显示当前值。