app中每一个setting都是preference的子类.用的最多的子类是checkBoxPreference/ListPreference/EditTextPreference。当这些子类不能满足我们的需求时，我们可以实现preference的子类。
可以在runtime是实现preference的子类，也可以在XML 中定义preference 。这些在XML中定义的preference也可以在runtime是修改.
checkBoxPreference/ListPreference/EditTextPreference 也可以用在XML中，对应xml中的标签，如： <CheckBoxPreference>。xml必须被放在res/xml中.
举例如下，一般res/xml中只能有一个xml文件.
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<CheckBoxPreference
android:key="pref_sync"
android:title="@string/pref_sync"
android:summary="@string/pref_sync_summ"
android:defaultValue="true" />
<ListPreference
android:dependency="pref_sync"
android:key="pref_syncConnectionType"
android:title="@string/pref_syncConnectionType"
android:dialogTitle="@string/pref_syncConnectionType"
android:entries="@array/pref_syncConnectionTypes_entries"
android:entryValues="@array/pref_syncConnectionTypes_values"
android:defaultValue="@string/pref_syncConnectionTypes_default" />
</PreferenceScreen>
需要注意的是可用 android:defaultValue 来设置默认值.
在这个例子中我们用到<ListPreference><CheckBoxPreference>标签.
如果setting 很多的话，可以考虑用group来分组
一个group中的setting可以用title 或者 subscreen来呈现.
如果要用title 来显示的话，将每个preference放到preferenceCategory中，如下所示：
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<PreferenceCategory
android:title="@string/pref_sms_storage_title"
android:key="pref_key_storage_settings">
<CheckBoxPreference
android:key="pref_key_auto_delete"
android:summary="@string/pref_summary_auto_delete"
android:title="@string/pref_title_auto_delete"
android:defaultValue="false"... />
<Preference
android:key="pref_key_sms_delete_limit"
android:dependency="pref_key_auto_delete"
android:summary="@string/pref_summary_delete_limit"
android:title="@string/pref_title_sms_delete"... />
<Preference
android:key="pref_key_mms_delete_limit"
android:dependency="pref_key_auto_delete"
android:summary="@string/pref_summary_delete_limit"
android:title="@string/pref_title_mms_delete" ... />
</PreferenceCategory>
...
</PreferenceScreen>
如果要用subscreen来显示的话.
将每个preference放到preferenceScreen中，如下所示
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<!-- opens a subscreen of settings -->
<PreferenceScreen
android:key="button_voicemail_category_key"
android:title="@string/voicemail"
android:persistent="false">
<ListPreference
android:key="button_voicemail_provider_key"
android:title="@string/voicemail_provider" ... />
<!-- opens another nested subscreen -->
<PreferenceScreen
android:key="button_voicemail_setting_key"
android:title="@string/voicemail_settings"
android:persistent="false">
...
</PreferenceScreen>
<RingtonePreference
android:key="button_voicemail_ringtone_key"
android:title="@string/voicemail_ringtone_title"
android:ringtoneType="notification" ... />
...
</PreferenceScreen>
...
</PreferenceScreen>
有时候想点击preference item的时候打开一个Activity而不是setting的界面。这时候可以用Intent来完成，例如打开浏览器看一个网页.
下面这个例子就会打开http://www.example.com
<Preference android:title="@string/prefs_web_page" >
<intent android:action="android.intent.action.VIEW"
android:data="http://www.example.com" />
</Preference>
如果想用Activity 来呈现setting，需要实现preferenceFragment的子类
public static class SettingsFragment extends PreferenceFragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Load the preferences from an XML resource
addPreferencesFromResource(R.xml.preferences);
}
...
}
可以通过设定默认值PreferenceManager.setDefaultValues(this, R.xml.advanced_preferences, false);
然后通过fragmentManager添加到你的Activity中.
public class SettingsActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Display the fragment as the main content.
getFragmentManager().beginTransaction()
.replace(android.R.id.content, new SettingsFragment())
.commit();
}
}
需要注意的是fragmentManager，没有context这个参数，如果你需要context这个参数，可以用getActivity()得到，注意getActivity()可以会得到NULL.
在某些情况下，当用户点击setting中的每一项是都会用subscreen来显示。可以参考下面的步奏
1：首先在xml中定义每一个PreferenceFragment。这些PreferenceFragment放置在header标签下.
<?xml version="1.0" encoding="utf-8"?>
<preference-headers xmlns:android="http://schemas.android.com/apk/res/android">
<header
android:fragment="com.example.prefs.SettingsActivity$SettingsFragmentOne"
android:title="@string/prefs_category_one"
android:summary="@string/prefs_summ_category_one" />
<header
android:fragment="com.example.prefs.SettingsActivity$SettingsFragmentTwo"
android:title="@string/prefs_category_two"
android:summary="@string/prefs_summ_category_two" >
<!-- key/value pairs can be included as arguments for the fragment. -->
<extra android:name="someKey" android:value="someHeaderValue" />
</header>
</preference-headers>
然后在PreferenceFragment 子类的onCreate函数中根据settings中的不同选项加载不同的xml文件.
public static class SettingsFragment extends PreferenceFragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String settings = getArguments().getString("settings");
if ("notifications".equals(settings)) {
addPreferencesFromResource(R.xml.settings_wifi);
} else if ("sync".equals(settings)) {
addPreferencesFromResource(R.xml.settings_sync);
}
}
}
在Activity中显示header
public class SettingsActivity extends PreferenceActivity {
@Override
public void onBuildHeaders(List<Header> target) {
loadHeadersFromResource(R.xml.preference_headers, target);
}
}
Reading Preferences
在你的application内部，可以通过调用静态方法来得到key—value的设定如下所示：
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
String syncConnPref = sharedPref.getString(SettingsActivity.KEY_PREF_SYNC_CONN, "");
Listening for preference changes
如果用户改变setting，我们可以通过实现OnSharePreferenceChangeListner来得到通知，如下所示：
public class SettingsActivity extends PreferenceActivity
implements OnSharedPreferenceChangeListener {
public static final String KEY_PREF_SYNC_CONN = "pref_syncConnectionType";
...
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
String key) {
if (key.equals(KEY_PREF_SYNC_CONN)) {
Preference connectionPref = findPreference(key);
// Set summary to be the user-description for the selected value
connectionPref.setSummary(sharedPreferences.getString(key, ""));
}
}
}
Building a Custom Preference
系统提供的preference子类不能满足你的需求的话，可以自己实现preference的子类.
1.当用户选择setting，用户可以看到的interface.
一般先实现一个DialogPreference 的子类，提供一个对话框给用户.
public class NumberPickerPreference extends DialogPreference {
public NumberPickerPreference(Context context, AttributeSet attrs) {
super(context, attrs);
setDialogLayoutResource(R.layout.numberpicker_dialog);
setPositiveButtonText(android.R.string.ok);
setNegativeButtonText(android.R.string.cancel);
setDialogIcon(null);
}
...
}
2.保存设定的值
可以调用 Preference 类的 persist*() 方法，如persistInt保存整数
@Override
protected void onDialogClosed(boolean positiveResult) {
// When the user selects "OK", persist the new value
if (positiveResult) {
persistInt(mNewValue);
}
}
3.初始化当前值。
当系统间你的preference添加到screen是，系统会call onSetInitialValue()来件事使用有一个persited value，如果没有的话，就设定一个默认值
@Override
protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
if (restorePersistedValue) {
// Restore existing state
mCurrentValue = this.getPersistedInt(DEFAULT_VALUE);
} else {
// Set default state from the XML attribute
mCurrentValue = (Integer) defaultValue;
persistInt(mCurrentValue);
}
}
如果你通过android:defaultValue 设定了默认值，系统来call onGetDefaultValue（）来取这个默认值.
@Override
protected Object onGetDefaultValue(TypedArray a, int index) {
return a.getInteger(index, DEFAULT_VALUE);
}
可以Activity的OnSaveInstanceState（）和OnRestoreInstanceState（）中保存和取回setting值。
一般会用BaseSavedState 的子类来保存，如下code所示：
private static class SavedState extends BaseSavedState {
// Member that holds the setting's value
// Change this data type to match the type saved by your Preference
int value;
public SavedState(Parcelable superState) {
super(superState);
}
public SavedState(Parcel source) {
super(source);
// Get the current preference's value
value = source.readInt(); // Change this to read the appropriate data type
}
@Override
public void writeToParcel(Parcel dest, int flags) {
super.writeToParcel(dest, flags);
// Write the preference's value
dest.writeInt(value); // Change this to write the appropriate data type
}
// Standard creator object using an instance of this class
public static final Parcelable.Creator<SavedState> CREATOR =
new Parcelable.Creator<SavedState>() {
public SavedState createFromParcel(Parcel in) {
return new SavedState(in);
}
public SavedState[] newArray(int size) {
return new SavedState[size];
}
};
}
@Override
protected Parcelable onSaveInstanceState() {
final Parcelable superState = super.onSaveInstanceState();
// Check whether this Preference is persistent (continually saved)
if (isPersistent()) {
// No need to save instance state since it's persistent,
// use superclass state
return superState;
}
// Create instance of custom BaseSavedState
final SavedState myState = new SavedState(superState);
// Set the state's value with the class member that holds current
// setting value
myState.value = mNewValue;
return myState;
}
@Override
protected void onRestoreInstanceState(Parcelable state) {
// Check whether we saved the state in onSaveInstanceState
if (state == null || !state.getClass().equals(SavedState.class)) {
// Didn't save the state, so call superclass
super.onRestoreInstanceState(state);
return;
}
// Cast state to custom BaseSavedState and pass to superclass
SavedState myState = (SavedState) state;
super.onRestoreInstanceState(myState.getSuperState());
// Set this Preference's widget to reflect the restored state
mNumberPicker.setValue(myState.value);
}
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