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
下面是一个基于@tdeveaux答案的PreferenceFragment内所有EditTextPreferences的工作解决方案:
public class SettingsFragment extends PreferenceFragment implements SharedPreferences.OnSharedPreferenceChangeListener {
private static final String TAG = "SettingsFragment";
@Override
public void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
}
@Override
public void onResume () {
super.onResume();
for (int i = 0; i < getPreferenceScreen().getPreferenceCount(); ++i) {
Preference preference = getPreferenceScreen().getPreference(i);
updatePreference(preference);
}
}
@Override
public void onSharedPreferenceChanged (SharedPreferences sharedPreferences, String key) {
updatePreference(findPreference(key));
}
private void updatePreference (Preference preference) {
if (preference instanceof EditTextPreference) {
EditTextPreference editTextPreference = (EditTextPreference)preference;
editTextPreference.setSummary(editTextPreference.getText());
}
}
}
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);
}
我的解决方案是创建一个自定义的EditTextPreference，像这样在XML中使用:EditTextPreference android:title="示例title " />
EditTextPreference.java: -
package com.example;
import android.content.Context;
import android.util.AttributeSet;
public class EditTextPreference extends android.preference.EditTextPreference
{
public EditTextPreference(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
}
public EditTextPreference(Context context, AttributeSet attrs)
{
super(context, attrs);
}
public EditTextPreference(Context context)
{
super(context, null);
}
@Override
protected void onDialogClosed(boolean positiveResult)
{
super.onDialogClosed(positiveResult);
setSummary(getSummary());
}
@Override
public CharSequence getSummary()
{
return getText();
}
}
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)
}
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"/>
如果你使用PreferenceFragment，这就是我解决它的方法。这是不言而喻的。
public static class SettingsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.settings);
getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
}
@Override
public void onResume() {
super.onResume();
for (int i = 0; i < getPreferenceScreen().getPreferenceCount(); ++i) {
Preference preference = getPreferenceScreen().getPreference(i);
if (preference instanceof PreferenceGroup) {
PreferenceGroup preferenceGroup = (PreferenceGroup) preference;
for (int j = 0; j < preferenceGroup.getPreferenceCount(); ++j) {
Preference singlePref = preferenceGroup.getPreference(j);
updatePreference(singlePref, singlePref.getKey());
}
} else {
updatePreference(preference, preference.getKey());
}
}
}
@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
updatePreference(findPreference(key), key);
}
private void updatePreference(Preference preference, String key) {
if (preference == null) return;
if (preference instanceof ListPreference) {
ListPreference listPreference = (ListPreference) preference;
listPreference.setSummary(listPreference.getEntry());
return;
}
SharedPreferences sharedPrefs = getPreferenceManager().getSharedPreferences();
preference.setSummary(sharedPrefs.getString(key, "Default"));
}
}
