creating a DialogPreference from XML
I have been attempting to use an android.preference.DialogPreference inflated from XML, but the documentation seems to be missing some essential bits, and I cannot find a working example anywhere. My XML now looks like this (I tried many permutations but this seems like a reasonable minimum):
<DialogPreference
android:key="funThing" android:title="Fun Thing"
android:dialogLayout="@layout/fun_layout"
android:positiveButtonText="OK"
android:negativeButtonText="Cancel"
/>
My supposition at this point is that it is required to subclass DialogPreference and not to use it directly. For one, I cannot find a way to associate the actual preference value with an element in the dialog itself, which upon reflection is kind of a giveaway. And also, looking at the source to DialogPreference.java seems to confirm it. And I also just noticed that the official documentation refers to it as a "base class". But at very least, it would be nice to establish a definitive-enough source on the net which would help the next N people figure this out faster than I did.
For the record, the logfile looks like this:
I/ActivityManager( 61): Starting: Intent { cmp=org.jeremy.android/.PreferencesActivity } from pid 2755
W/Resources( 2755): Converting to string: TypedValue{t=0x10/d=0x4b0 a=-1}
W/Resources( 2755): Converting to string: TypedValue{t=0x10/d=0x20 a=-1}
D/AndroidRuntime( 2755): Shutting down VM
W/dalvikvm( 2755): threadid=1: thread exiting with uncaught exception (group=0x40015560)
E/AndroidRuntime( 2755): FATAL EXCEPTION: main
E/AndroidRuntime( 2755): java.lang.RuntimeException: Unable to start activity ComponentInfo{org.jeremy.android/org.jeremy.android.PreferencesActivity}: android.view.InflateException: Binary XML file line #28: Error inflating class java.lang.reflect.Constructor
E/AndroidRuntime( 2755): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
E/AndroidRuntime( 2755): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
E/AndroidRuntime( 2755): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
E/AndroidRuntime( 2755): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
E/AndroidRuntime( 2755): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 2755): at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 2755): at android.app.ActivityThread.main(ActivityThread.java:3683)
E/AndroidRuntime( 2755): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 2755): at java.lang.reflect.Method.invoke(Method.java:507)
E/AndroidRuntime( 2755): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
E/AndroidRuntime( 2755): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
E/AndroidRuntime( 2755): at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime( 2755): Caused by: android.view.InflateException: Binary XML file line #28: Error inflating class java.lang.reflect.Constructor
E/AndroidRuntime( 2755): at android.preference.GenericInflater.createItem(GenericInflater.java:397)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.onCreateItem(GenericInflater.java:417)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.createItemFromTag(GenericInflater.java:428)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.rInflate(GenericInflater.java:481)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.rInflate(GenericInflater.java:493)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.inflate(GenericInflater.java:326)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.inflate(GenericInflater.java:263)
E/AndroidRuntime( 2755): at android.preference.PreferenceManager.inflateFromResource(PreferenceManager.java:251)
E/AndroidRuntime( 2755): at android.preference.PreferenceActivity.addPreferencesFromResource(PreferenceActivity.java:262)
E/AndroidRuntime( 2755): at org.jeremy.android.PreferencesActivity.onCreate(PreferencesActivity.java:40)
E/AndroidRuntime( 2755): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
E/AndroidRuntime( 2755): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
E/AndroidRuntime( 2755): ... 11 more
E/AndroidRuntime( 2755): Caused by: java.lang.InstantiationException: android.preference.DialogPreference
E/AndroidRuntime( 2755): at java.lang.reflect.Constructor.constructNative(Native Method)
E/AndroidRuntime( 2755): at java.lang.reflect.Constructor.newInstance(Constructor.java:415)
E/AndroidRuntime( 2755): at android.preference.GenericInflater.createItem(GenericInflater.java:383)
E/AndroidRuntime( 2755): ... 22 more
W/ActivityManager( 61): Force finishing activity org.jeremy.android/.PreferencesActivity
W/ActivityManager( 61): Force finishing activity org.jeremy.android/.SplashActivity
Solution 1:
Here is an example of how to use the dialog preference (subclassing as you mentioned).
package dk.myapp.views;
import android.content.Context;
import android.preference.DialogPreference;
import android.util.AttributeSet;
/**
* The OptionDialogPreference will display a dialog, and will persist the
* <code>true</code> when pressing the positive button and <code>false</code>
* otherwise. It will persist to the android:key specified in xml-preference.
*/
public class OptionDialogPreference extends DialogPreference {
public OptionDialogPreference(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onDialogClosed(boolean positiveResult) {
super.onDialogClosed(positiveResult);
persistBoolean(positiveResult);
}
}
The preferences.xml should contain
<dk.myapp.views.OptionDialogPreference
android:key="@string/prefKeyResetQuests"
android:dialogIcon="@android:drawable/ic_dialog_alert"
android:title="Reset Quests"
android:summary="Reset all quest-progress."
android:dialogMessage="Are you sure you wish to reset your quest progress? This action cannot be undone!"
android:positiveButtonText="Clear Quests"
android:negativeButtonText="Cancel"/>
I have a res/value containing (though the key-name can also be declared explicitly above).
<string name="prefKeyResetQuests">resetQuests</string>
My PreferenceActivity does the actual resetting from onPause. Note that onStop may be too late since the onStop will not always be called immediately after pressing back:
@Override
public void onPause() {
SharedPreferences prefs = android.preference.PreferenceManager.
getDefaultSharedPreferences(getBaseContext());
if(prefs.getBoolean(
getResources().getString(R.string.prefKeyResetQuests), false)) {
// apply reset, and then set the pref-value back to false
}
}
Or equivalently since we are still in the PreferenceActivity:
@Override
protected void onPause() {
Preference prefResetQuests =
findPreference(getResources().getString(R.string.prefKeyResetQuests));
if(prefResetQuests.getSharedPreferences().
getBoolean(prefResetQuests.getKey(), false)){
// apply reset, and then set the pref-value back to false
}
}
Solution 2:
This one is weird, you need to subclass DialogPreference. The subclass does not need to do anything. So
public class MyDialogPreference extends DialogPreference {
public MyDialogPreference(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
}
can be instantiated. While a plane old DialogPreference can not. Very weird, they should be the exact same thing.
Solution 3:
First:
Create your own class which extends DialogPreference as bellow:
package com.test.view;
import android.preference.DialogPreference;
public class DialogExPreference extends DialogPreference
{
public DialogExPreference(Context oContext, AttributeSet attrs)
{
super(oContext, attrs);
}
}
Second:
Modify the xml file as bellow:
<PreferenceScreen
xmlns:android="http://schemas.android.com/apk/res/android">
<com.test.view.DialogExPreference
android:title="@string/title"
android:dialogMessage="@string/lite"
android:negativeButtonText="test"/>
</PreferenceScreen>
Then it's OK.