Android Preferences: How to load the default values when the user hasn't used the preferences-screen?

I am using a PreferenceActivity to let the user set some values. I am feeding it the xml file with the defined preferences.

I have set all the android:defaultValue="" for them.

When I start my application, I need the preferences, or if they are not set yet manually, I want the default values:

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
boolean value = prefs.getBoolean("key"), false);

However, when android:defaultValue="true" I still get false. So, it looks like the defaultValues set in the XML are not used anywhere but when initializing the preferences-screen.

I don't want to hardcode the default values in the getBoolean() method. So, is there a way get the default-values with only defining these in 1 place?

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For example extending DialogPreference I do this:

@Override
protected void onSetInitialValue(boolean restore, Object defaultValue) {
super.onSetInitialValue(restore, defaultValue);


if (restore) {
mValue = shouldPersist() ? getPersistedString(mDefault) : mDefault;
} else {
mValue = mDefault;
}
}

mDefault can be:

  • mContext.getResources().getString(attrs.getAttributeResourceValue(androidns,"defaultValue", 100));
  • something you have indexed in R.
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最佳答案

this question is similar to mine:

initialize-preferences-from-xml-in-main-activity

Just use this code in onCreate method:

PreferenceManager.setDefaultValues(this, R.xml.preference, false);

It will load your preferences from XML, and last parameter (readAgain) will guarantee that user preferences won't be overwritten. That means setting the readAgain argument to false means this will only set the default values if this method has never been called in the past so you don't need to worry about overriding the user's settings each time your Activity is created

Take a look into PreferenceManager.setDefaultValues in Android API for further investigation.

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Be aware that if you are using
getSharedPreferences(String sharedPreferencesName, int sharedPreferencesMode)

to retrieve preferences you have to use
PreferenceManager.setDefaultValues(Context context, String sharedPreferencesName, int sharedPreferencesMode, int resId, boolean readAgain)
to set defaults!

For example:
PreferenceManager.setDefaultValues(this, PREFS_NAME, Context.MODE_PRIVATE, R.xml.preference, false);

I hope this can help someone.

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in Pixel's accepted answer:

PreferenceManager.setDefaultValues(this, R.xml.preference, false);

it is stated that the false means that defaults won't be overwritten. This is not what it does, it is just an efficiency flag to stop the parsing if your application has more than one entry point. Unfortunately the test is not made per preference file, so if you have more than one preference file you must code true on all but the first.

If you are worried about efficiency, you could code something like this.

final static private int SPL = 1;
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
if (sp.getInt("spl", 0) != SPL)
{
PreferenceManager.setDefaultValues(this, R.xml.prefs1, true);
PreferenceManager.setDefaultValues(this, R.xml.prefs2, true);
sp.edit().putInt("spl", SPL).apply();
}

If you ever add more shared preferences, just set SPL to a hight number.

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Also make sure you have never used the SharedPreferences before. To make sure they are not changed (which means setDefaultValues(this,xml,false) has no effect) uninstall your App and upload it again to be sure no values are touched. This helped me.

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define class extends android.preference.Preference

public class IntegerPreference extends Preference {
public IntegerPreference(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}


public IntegerPreference(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}


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


public IntegerPreference(Context context) {
super(context);
}


@Override
protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
super.onSetInitialValue(restorePersistedValue, defaultValue);
persistInt((Integer) defaultValue);
}


@Override
protected Object onGetDefaultValue(TypedArray a, int index) {
return a.getInt(index, -1);
}
}


public class StringSetPreference extends Preference {
public StringSetPreference(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
}


public StringSetPreference(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}


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


public StringSetPreference(Context context) {
super(context);
}


@Override
protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
super.onSetInitialValue(restorePersistedValue, defaultValue);
persistStringSet((Set<String>) defaultValue);
}


@Override
protected Object onGetDefaultValue(TypedArray a, int index) {
return Stream.of(a.getTextArray(index)).map(String::valueOf).collect(Collectors.toSet());
}
}

define preference XML resource

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<com.ainirobot.preferencetest.IntegerPreference
android:defaultValue="101"
android:key="III" />
<com.ainirobot.preferencetest.FloatPreference
android:defaultValue="1.2"
android:key="FFF" />
<com.ainirobot.preferencetest.StringPreference
android:defaultValue="SSS"
android:key="SSS" />
<com.ainirobot.preferencetest.BooleanPreference
android:defaultValue="True"
android:key="BBB" />
<com.ainirobot.preferencetest.StringSetPreference
android:defaultValue="@array/sset"
android:key="SSET" />
</PreferenceScreen>

then initialize default value and access

    PreferenceManager.setDefaultValues(this, R.xml.preferences, false);


Map<String, ?> allKeys = PreferenceManager.getDefaultSharedPreferences(this).getAll();
int iii = PreferenceManager.getDefaultSharedPreferences(this).getInt("III", -1);
float fff = PreferenceManager.getDefaultSharedPreferences(this).getFloat("FFF", 0);
Log.d(TAG, "allKeys=" + allKeys + " iii=" + iii + " fff=" + fff);

//Logcat

10-13 06:53:06.986 12594 12594 D MainActivity: allKeys={III=101, BBB=true, SSS=SSS, FFF=1.2, SSET=[XXX, ZZZ, YYY]} iii=101 fff=1.2

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