HowTo use support.v7.preference with AppCompat and potential drawbacks

问题

I was trying to implement preferences for an AppCompat app, using support.v7.preference. It took me a couple of days to fiddle through it, since support.v7.preference has some significant differences to the native preferences... which isn't too bad once you know, but unfortunately there's little documentation out there. I thought I'd share my findings so others don't have to go through the same pain.

So... question:

How do you best implement Preferences for AppCompat apps (with PreferenceFragment and AppCompatAcitivity being incompatible)?

Here are a couple of related questions:

Preference sub-screen not opening when using support.v7.preference
How to move back from Preferences subscreen to main screen in PreferenceFragmentCompat?
PreferenceFragmentCompat requires preferenceTheme to be set
How do I create custom preferences using android.support.v7.preference library?

Official docs here:

http://developer.android.com/guide/topics/ui/settings.html
http://developer.android.com/reference/android/support/v7/preference/Preference.html

回答1:

Solution 1: Native `PreferenceFragment` with `AppCompatActivity`

In AndroidStudio, choose File > New Project >...> SettingsActivity. This template uses a workaround that retrofits the native PreferenceFragment to work with AppCompatActivity, similar to the support.v4.Fragment or the support.v7.PreferenceFragmentCompat.

Pro: you can now use the native Preference functionality within an AppCompat app. It's a quick approach when using the AS template, and you can stick to the existing Preference docs and workflows.
Con: the retrofitting isn't very intuitive or clean. Also since it's usually advisable to use support libs where available, I'm not sure how future-proof this approach is.

Solution 2: `support.v7.preference.PreferenceFragmentCompat` with `AppCompatActivity`

Pro: maximizes compatibility
Con: a lot of gaps to bridge. Also this might not work with any of the existing preference-extensions-libs out there (eg. ColorPicker or FontPreferences).

Should you choose not to use Solution 1 (I'm still not sure which of the two is more future proof), there are a couple of drawbacks when using support.v7.preference.

Important drawbacks of using Solution 2 are mentioned below.

Dependencies:

dependencies {
    ...
    compile 'com.android.support:appcompat-v7:23.1.1'
    compile 'com.android.support:preference-v7:23.1.1'
    compile 'com.android.support:support-v4:23.1.1'
}

Theme: You'll need to define a preferenceTheme in your styles.xml, otherwise running your app will raise an exception.

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light">
    <!-- Customize your theme here. -->
    <item name="preferenceTheme">@style/PreferenceThemeOverlay</item>
</style>

You might wanna split this into different styles for 7+/14+/21+. A lot of people complain about this being buggy at the time of this writing. There is a very comprehensive answer available here.

Behavior changes: using the native preferences is extremely straight forward: all you need to do is define/maintain your preferences.xml and use addPreferencesFromResource(R.xml.preferences) within your PreferenceFragment. Custom preferences are easily done by sub-classing DialogPreference, and then just referenced to within the preferences.xml... bam, works.

Unfortunately, support.v7.preference has had everything related to dealing with Fragment stripped out, making it loose a lot of it's built-in functionality. Instead of just maintaining an XML, you now have to sub-class and override a lot of stuff, all of which is unfortunately undocumented.

PreferenceScreens: PreferenceScreens are no longer managed by the framework. Defining a PreferenceScreen in your preference.xml (as described in the docs) will display the entry, but clicking on it does nothing. It's now up to you to deal with displaying and navigating sub-screens. Boring.

There is one approach (described here), adding a PreferenceFragmentCompat.OnPreferenceStartScreenCallback to your PreferenceFragmentCompat. While this approach is quickly implemented, it simply swaps the content of the existing preference fragment. Downside is: there is no back navigation, you're always 'at the top', which isn't very intuitive for the user.

In another approach (described here), you'll also have to manage the back stack in order to achieve back navigation as expected. This uses preferenceScreen.getKey() as a root for each newly created/displayed fragment.

When doing so, you might also stumble over the PreferenceFragments being transparent by default and adding up oddly on top of each other. People tend to override PreferenceFragmentCompat.onViewCreated() to add something like

// Set the default white background in the view so as to avoid transparency
view.setBackgroundColor(ContextCompat.getColor(getContext(), R.color.background_material_light));

Custom DialogPreference: Making your own preferences has also gone from trivial to boring. DialogPreference now has anything that deals with the actual dialog, removed. That bit now lives in PreferenceDialogFragmentCompat. So you'll have to sub-class both, then deal with creating the dialog and displaying it yourself (explained here).

Looking at the source of PreferenceFragmentCompat.onDisplayPreferenceDialog() shows that it knows how to deal with exactly 2 dialog preferences (EditTextPreference, ListPreference), everything else you'll have to implement yourself using OnPreferenceDisplayDialogCallbacks... one wonders, why there is no functionality to handle sub-class of DialogPreference!

Here is some code that implements most of these workarounds and boxes them in a lib module:

https://github.com/mstummer/extended-preferences-compat.git

Main intentions were:

Remove the need to extend and fiddle with Activity and PreferenceFragment in each app/projects. preference.xml is now again the only per-project file to change/maintain.
Handle and display PreferenceScreens (sub-screens) as expected.
Un-split DialogPreference to restore the native behavior.
Handle and display any sub-class of DialogPreference.

Don't think it's clean enough to be just used out of the box, but it might give you some hints when dealing with similar issues. Give it a spin and let me know if you've got any suggestions.

回答2:

I have an alternative solution to this, that i'd love feedback on.

I made a custom layout for my preferencefragment, with a "Back" button in the upper left corner.

First, in the "onCreatePreference" i store away the root PreferenceScreen:

root = this.getPreferenceScreen();

Then, I add the OnPreferenceStartScreenCallback as described above and in other threads to make the fragment go to subscreen, but in my "onPreferenceStartScreen" i also set the back button to visible like this:

    public boolean onPreferenceStartScreen(PreferenceFragmentCompat preferenceFragmentCompat, PreferenceScreen preferenceScreen) {
        preferenceFragmentCompat.setPreferenceScreen(preferenceScreen);
        backButton.setVisibility(View.VISIBLE);
        return true;
}

Finally, the backButton clickhandler:

    setPreferenceScreen(root);
    back.setVisibility(View.GONE);

This seem to work fine for me. Obviously the back stack won't work, but i can live with that since there is a Back button.

Not perfect, but given the abysmal API i think i'm happy.

I would love to hear if someone thinks there are any problems with this approach.

来源：https://stackoverflow.com/questions/34983932/howto-use-support-v7-preference-with-appcompat-and-potential-drawbacks

标签

android

android-appcompat

android-preferences

preferencescreen

preference-v7