How do I create custom preferences using android.support.v7.preference library?

Question

I want to support at least api 10, I want to be able to style my preferences nicely, I want to be able to have headers (or to show PreferenceScreens). It seems that PreferenceActivity, not fully supported by AppCompat's coloring, will not fit. So I'm trying to use AppCompatActivity and PreferenceFragmentCompat.

public class Prefs extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (savedInstanceState == null)
            getSupportFragmentManager().beginTransaction()
                    .replace(android.R.id.content, new PreferencesFragment())
                    .commit();
    }

    public static class PreferencesFragment extends PreferenceFragmentCompat {
        @Override public void onCreate(final Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            addPreferencesFromResource(R.xml.preferences);
        }

        @Override
        public void onDisplayPreferenceDialog(Preference preference) {
            // the following call results in a dialogue being shown
            super.onDisplayPreferenceDialog(preference);
        }

        @Override public void onNavigateToScreen(PreferenceScreen preferenceScreen) {
            // I can probably use this to go to to a nested preference screen
            // I'm not sure...
        }
    }
}

Now, I want to create a custom preference that will provide the choice of a font. With PreferenceActivity, I could simply do

import android.preference.DialogPreference;

public class FontPreference extends DialogPreference {

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

    @Override protected void onPrepareDialogBuilder(Builder builder) {
        super.onPrepareDialogBuilder(builder);
        // do something with builder and make a nice cute dialogue, for example, like this
        builder.setSingleChoiceItems(new FontAdapter(), 0, null);
    }
}

and use xml such as this to display it

<my.app.FontPreference android:title="Choose font" android:summary="Unnecessary summary" />

But now, there is no onPrepareDialogBuilder in android.support.v7.preference.DialogPreference. Instead, it's been moved to PreferenceDialogFragmentCompat. I found little information on how to use that thing, and I'm not sure how to go from xml to displaying it. v14 preference fragment has the following code:

public void onDisplayPreferenceDialog(Preference preference) {
    ...

    final DialogFragment f;
    if (preference instanceof EditTextPreference)
        f = EditTextPreferenceDialogFragment.newInstance(preference.getKey());
    ...
    f.show(getFragmentManager(), DIALOG_FRAGMENT_TAG);
}

I tried subclassing android.support.v7.preference.DialogPreference and having onDisplayPreferenceDialog use a similar piece of code to instantiate a dummy FontPreferenceFragment but it fails with the following exception.

java.lang.IllegalStateException: Target fragment must implement TargetFragment interface

At this point I'm already too deep into the mess and don't want to dig further. Google knows nothing about this exception. Anyways, this method seems to be overly complicated. So, what's the best way to create custom preferences using android.support.v7.preference library?

Answer 1

Important note: Currently (v23.0.1 of the v7 library) there are still a lot of theme-issues with the 'PreferenceThemeOverlay'(see this issue). On Lollipop for example, you end up with Holo-styled category headers.

After some frustrating hours, I finally succeeded to create a custom v7 Preference. Creating your own Preference appears to be harder than you might think is needed. So make sure to take some time.

At first you might be wondering why you will find both a DialogPreference and a PreferenceDialogFragmentCompat for each preference type. As it turns out, the first one is the actual preference, the second is the DialogFragment where the preference would be displayed in. Sadly, you are required to subclass both of them.

Don't worry, you won't need to change any piece of code. You only need to relocate some methods:

• All preference-editing methods (like setTitle() or persist*()) can be found in the DialogPreference class.
• All dialog (-editing) methods (onBindDialogView(View) & onDialogClosed(boolean)) have been moved to PreferenceDialogFragmentCompat.

You might want your existing class to extend the first one, that way you don't have to change to much I think. Autocomplete should help you find missing methods.

When you have completed the above steps, it is time to bind these two classes together. In your xml file, you will refer to the preference-part. However, Android doesn't know yet which Fragment it must inflate when your custom preference needs to be. Therefore, you need to override onDisplayPreferenceDialog(Preference):

@Override
public void onDisplayPreferenceDialog(Preference preference) {
    DialogFragment fragment;
    if (preference instanceof LocationChooserDialog) {
        fragment = LocationChooserFragmentCompat.newInstance(preference);
        fragment.setTargetFragment(this, 0);
        fragment.show(getFragmentManager(),
                "android.support.v7.preference.PreferenceFragment.DIALOG");
    } else super.onDisplayPreferenceDialog(preference);
}

and also your DialogFragment needs to handle the 'key':

public static YourPreferenceDialogFragmentCompat newInstance(Preference preference) {
    YourPreferenceDialogFragmentCompat fragment = new YourPreferenceDialogFragmentCompat();
    Bundle bundle = new Bundle(1);
    bundle.putString("key", preference.getKey());
    fragment.setArguments(bundle);
    return fragment;
}

That should do the trick. If you encounter problems, try taking a look at existing subclasses and see how Android solved it (in Android Studio: type a class' name and press Ctrl+b to see the decompiled class). Hope it helps.

Answer 2

The exception is caused when your FontPreferenceFragment does not implement DialogPreference.TargetFragment. You'll need to make sure your fragment implements that interface.