How to use the v7/v14 Preference Support library?

问题:

Together with the M release, there are new support libraries. One of them that seems to be very useful is the v7 Preference Support library.

It does not seem to have PreferenceActivity or something similar, how do we integrate it to our app?

回答1:

You have to extend AppCompatActivity, which is required for fragment, and include a subclass of PreferenceFragmentCompat. The abstract fragment requires to override one method, in which you should place your preference inflation logic. And last, your activity theme needs to specify a preferenceTheme attribute.

Read the announcement here. With preference-v7 library you can replace PreferenceFragment (API 11+) with PreferenceFragmentCompat subclass, and SwitchPreference (API 14+) with SwitchPreferenceCompat and have your settings screen work from API 7.

Below is how I made it work:

SettingsActivity.java

public class SettingsActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
    }
}

layout/activity_settings.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent" >
    <fragment
        android:name=".SettingsFragment"
        android:tag=".SettingsFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</FrameLayout>

SettingsFragment.java

public class SettingsFragment extends PreferenceFragmentCompat {

    @Override
    public void onCreatePreferences(Bundle bundle, String s) {
        addPreferencesFromResource(R.xml.preferences);
    }
}

xml/preferences.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.preference.PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <android.support.v7.preference.PreferenceCategory
        ...>

        <android.support.v7.preference.ListPreference
            ... />

        <android.support.v7.preference.SwitchPreferenceCompat
            ... />

        ...

    </android.support.v7.preference.PreferenceCategory>

    ...

</android.support.v7.preference.PreferenceScreen>

values/styles.xml

<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
    <item name="preferenceTheme">@style/PreferenceThemeOverlay</item>
    ...
</style>

preference-v7 default theme

<style name="PreferenceThemeOverlay">
    <item name="preferenceScreenStyle">@style/Preference.PreferenceScreen</item>
    <item name="preferenceFragmentStyle">@style/PreferenceFragment</item>
    <item name="preferenceCategoryStyle">@style/Preference.Category</item>
    <item name="preferenceStyle">@style/Preference</item>
    <item name="preferenceInformationStyle">@style/Preference.Information</item>
    <item name="checkBoxPreferenceStyle">@style/Preference.CheckBoxPreference</item>
    <item name="switchPreferenceCompatStyle">@style/Preference.SwitchPreferenceCompat</item>
    <item name="dialogPreferenceStyle">@style/Preference.DialogPreference</item>
    <item name="editTextPreferenceStyle">@style/Preference.DialogPreference.EditTextPreference</item>
    <item name="preferenceFragmentListStyle">@style/PreferenceFragmentList</item>
</style>

回答2:

hidro's answer is right but one more thing here to notice:

Just use normal preference xml tags such as PreferenceScreen instead of the full class name. The support library will convert them automatically.

Why: If you use the full class name the code suggestion and layout preview will not work properly.

So you should write xml like this:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">

    <PreferenceCategory
        ...>

        <ListPreference
            ... />

        <SwitchPreferenceCompat
            ... />

        ...

    </PreferenceCategory>

    ...

</PreferenceScreen>

回答3:

With the new preference support library v7 you can use the PreferenceFragmentCompat with any Activity or AppCompatActivity

public static class PrefsFragment extends PreferenceFragmentCompat {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Load the preferences from an XML resource
        addPreferencesFromResource(R.xml.preferences);
    }
}

You have to set preferenceTheme in your theme:

<style name="AppTheme" parent="@style/Theme.AppCompat.Light">
  ...
  <item name="preferenceTheme">@style/PreferenceThemeOverlay</item>
</style>

In this way you can customize the preferenceTheme to style the layouts used for each preference type without affecting other parts of your Activity.

回答4:

You are right it doesn't exist on the appcompat v7, but Google actually added AppCompatDelegate abstract class as a delegate you can use to inject the AppCompat's support to any activity. You can find more from this answer.

This is an example of how to inject the AppCompatDelegate into your activity from the AppCompat's samples from Google, You can find it here.

回答5:

I tried to implement Hidro's answer above with an activity which also contained a toolbar and it gave me the following a layout inflation exception because of the following error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.support.v4.app.FragmentHostCallback.getContext()' on a null object reference

I haven't been able to solve these, so have resorted to the following:

public class SettingsActivity extends AppCompatActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  if(savedInstanceState == null)
    getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, new SettingsFragment()).commit();
  }
}

With the following layout for the SettingsActivity:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:fitsSystemWindows="true">
  <include layout="@layout/toolbar"/>
  <FrameLayout android:id="@+id/fragment_container"
               android:layout_width="match_parent"
               android:layout_height="match_parent"
               app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>

Posted here as it may help if other people encounter the same exception