Question

I am trying to get an example from the book Professional Android Programming with Mono for Android and .Net/C#
(pages 202 to 204) working.

To register and unregister a change listener it shows the following code sample:

using System;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Preferences;

namespace MonoForAndroidPreferences
{
    [Activity(Label = "User Preferences")]
    public class UserPreferences : PreferenceActivity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Create your application here
            this.AddPreferencesFromResource(Resource.Layout.userpreferences);
        }

        protected override void OnResume()
        {
            base.OnResume();

            this.GetPreferences(FileCreationMode.Private).RegisterOnSharedPreferenceChangeListener(this);
        }

        protected override void OnPause()
        {
            base.OnPause();

            this.GetPreferences(FileCreationMode.Private).UnregisterOnSharedPreferenceChangeListener(this);
        }

        public void OnSharedPreferenceChanged(ISharedPreferences prefs, string key)
        {
            // Do something with the changed value pointed to by key
        }
    }
}

Both RegisterOnSharedPreferenceChangeListener and UnregisterOnSharedPreferenceChangeListener of course cannot convert from UserPreferences to ISharedPreferencesOnSharedPreferenceChangeListener.

I’m not sure how the author meant for this to work. Any help would be greatly appreciated.

I also tried downloading the sample code from wrox.com but it did not include the listening for preferences changes in the sample code.

EDIT:

The following code compiles, but OnSharedPreferenceChanged never gets called when an update is made in the preferences.

    public class UserPreferences : PreferenceActivity, ISharedPreferencesOnSharedPreferenceChangeListener
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Create your application here
            this.AddPreferencesFromResource(Resource.Layout.userpreferences);
        }

        protected override void OnResume()
        {
            base.OnResume();

            this.GetPreferences(FileCreationMode.Private).RegisterOnSharedPreferenceChangeListener(this);
        }

        protected override void OnPause()
        {
            base.OnPause();

            this.GetPreferences(FileCreationMode.Private).UnregisterOnSharedPreferenceChangeListener(this);
        }

        void ISharedPreferencesOnSharedPreferenceChangeListener.OnSharedPreferenceChanged(ISharedPreferences prefs, string key)
        {
            // Do something with the changed value pointed to by key
        }
    }

Answer 1

You need to use

PreferenceScreen.SharedPreferences.RegisterOnSharedPreferenceChangeListener(this);

instead of

 this.GetPreferences(FileCreationMode.Private).RegisterOnSharedPreferenceChangeListener(this);