Question

我收到此异常

原因：java.lang.ClassCastException：androidx.preference.PreferenceScreen无法转换为android.preference.GenericInflater $ Parent

关于做PreferenceManager.setDefaultValues(this, R.xml.root_preferences, false);
在主要活动中。

根据this的帖子，如果清单文件中的活动及其父项相同，但我却不是这种情况，则会发生上述错误。我只是不明白为什么会抛出该异常。

AndroidManifest.xml

         <activity
                android:name=".SettingsActivity"
                android:label="@string/title_activity_settings"
                android:parentActivityName=".MainActivity">
                <meta-data
                    android:name="android.support.PARENT_ACTIVITY"
                    android:value="com.example.android.droidcafeinput.MainActivity" />
            </activity>
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

root_preferences.xml

<androidx.preference.PreferenceScreen xmlns:app="http://schemas.android.com/apk/res-auto">

    <PreferenceCategory app:title="@string/messages_header">

        <EditTextPreference
            app:key="signature"
            app:title="@string/signature_title"
            app:useSimpleSummaryProvider="true" />

        <ListPreference
            app:defaultValue="reply"
            app:entries="@array/reply_entries"
            app:entryValues="@array/reply_values"
            app:key="reply"
            app:title="@string/reply_title"
            app:useSimpleSummaryProvider="true" />

    </PreferenceCategory>

    <PreferenceCategory app:title="@string/sync_header">

        <SwitchPreferenceCompat
            app:key="sync"
            app:title="@string/sync_title" />

        <SwitchPreferenceCompat
            app:dependency="sync"
            app:key="attachment"
            app:summaryOff="@string/attachment_summary_off"
            app:summaryOn="@string/attachment_summary_on"
            app:title="@string/attachment_title" />

    </PreferenceCategory>

</androidx.preference.PreferenceScreen>

SettingsActivity.java

public class SettingsActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.settings_activity);
        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.settings, new SettingsFragment())
                .commit();
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null) {
            actionBar.setDisplayHomeAsUpEnabled(true);
        }
    }

    public static class SettingsFragment extends PreferenceFragmentCompat {
        @Override
        public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
            setPreferencesFromResource(R.xml.root_preferences, rootKey);
        }
    }
}

Stacktrace

Caused by: Java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.droidcafeinput/com.example.android.droidcafeinput.MainActivity}: java.lang.ClassCastException: androidx.preference.PreferenceScreen cannot be cast to android.preference.GenericInflater$Parent
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: java.lang.ClassCastException: androidx.preference.PreferenceScreen cannot be cast to android.preference.GenericInflater$Parent
        at android.preference.GenericInflater.inflate(GenericInflater.java:321)
        at android.preference.GenericInflater.inflate(GenericInflater.java:264)
        at android.preference.PreferenceManager.inflateFromResource(PreferenceManager.java:324)
        at android.preference.PreferenceManager.setDefaultValues(PreferenceManager.java:650)
        at android.preference.PreferenceManager.setDefaultValues(PreferenceManager.java:609)
        at com.example.android.droidcafeinput.MainActivity.onCreate(MainActivity.java:74)
        at android.app.Activity.performCreate(Activity.java:6975)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6541) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

好像您正在尝试将android.preference.PreferenceManager与AndroidX库一起使用。这些库不兼容：由于您在其他地方使用了AndroidX库，因此请确保您没有任何android.preference导入。另外，在AndroidX库中，您无需调用setDefaultValues，因为默认值是自动读取和使用的-如果您删除该行，它应该可以工作。

在PreferenceManager.setDefaultValues（）

1 个答案: