从设置首选项获取值时获取空指针异常

Question

在我的应用程序中，我在 xml 文件夹中创建了设置首选项，并使用该方法将其分配给首选项管理器。但是当我试图从 SharedPreferences 中获取值时，它抛出了空指针异常....

public class RemindMe extends Application {

//  private static final String TAG = "RemindMe";

    public static SqliteServiceProvider dbHelper;
    public static SQLiteDatabase db;
    public static SharedPreferences sp;

    public static final String TIME_OPTION = "time_option";
    public static final String DATE_RANGE = "date_range";
    public static final String DATE_FORMAT = "date_format";
    public static final String TIME_FORMAT = "time_format";
    public static final String VIBRATE_PREF = "vibrate_pref";
    public static final String RINGTONE_PREF = "ringtone_pref";

    public static final String DEFAULT_DATE_FORMAT = "yyyy-M-d";

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

        PreferenceManager.setDefaultValues(this, R.xml.settings, false);
        sp = PreferenceManager.getDefaultSharedPreferences(this);

        dbHelper = new SqliteServiceProvider(this);
        db = dbHelper.getWritableDatabase();        
    }

    public static boolean showRemainingTime() {
        return "1".equals(sp.getString(TIME_OPTION, "0"));
    }

    public static int getDateRange() {
        return Integer.parseInt(sp.getString(DATE_RANGE, "0"));
//      return 0;
    }

    public static String getDateFormat() {
        return sp.getString(DATE_FORMAT, DEFAULT_DATE_FORMAT);
    }   

    public static boolean is24Hours() {
        return sp.getBoolean(TIME_FORMAT, true);
    }

    public static boolean isVibrate() {
        return sp.getBoolean(VIBRATE_PREF, true);
    }

    public static String getRingtone() {
        return sp.getString(RINGTONE_PREF, android.provider.Settings.System.DEFAULT_NOTIFICATION_URI.toString());
    }

}

这是我的设置偏好

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">

    <PreferenceCategory android:title="Display Settings">

        <ListPreference android:key="time_option"
            android:title="Display Time"
            android:summary="Actual"
            android:entries="@array/time_option_arr"
            android:entryValues="@array/val_arr"
            android:defaultValue="0" />

        <ListPreference android:key="date_range"
            android:title="Date Range"
            android:summary="Daily"
            android:entries="@array/date_range_arr"
            android:entryValues="@array/val_arr"
            android:defaultValue="0" />

        <ListPreference android:key="date_format"
            android:title="Date Format"
            android:summary="yyyy-M-d"
            android:entries="@array/date_format_arr"
            android:entryValues="@array/date_format_arr"
            android:defaultValue="yyyy-M-d" />

        <CheckBoxPreference android:key="time_format"
            android:title="Time Format"
            android:summary="Use 24-hour format"
            android:defaultValue="true" />

    </PreferenceCategory>

    <PreferenceCategory android:title="Notification Settings">

        <CheckBoxPreference android:key="vibrate_pref"
            android:title="Vibrate"
            android:summary="Vibrate on notification"
            android:defaultValue="true" />

        <RingtonePreference android:key="ringtone_pref"
            android:title="Set Ringtone"
            android:summary="Default"
            android:ringtoneType="all"
            android:showDefault="true"
            android:showSilent="false" />

        <!--Preference android:key="about_pref"
            android:title="About"
            android:summary="Credits" /-->

    </PreferenceCategory>

</PreferenceScreen>

这里是堆栈跟踪...

FATAL EXCEPTION: main java.lang.RuntimeException: Unable to resume activity {info.androidhive.navigationdrawer/info.androidhive.navigationdrawer.task_classes.AddAlarmActivity}: java.lang.NullPointerException at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2943) at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2972) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2407) at android.app.ActivityThread.access0(ActivityThread.java:162) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1368) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5410) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at info.androidhive.navigationdrawer.task_classes.RemindMe.getDateFormat(RemindMe.java:53) at info.androidhive.navigationdrawer.task_classes.AddAlarmActivity.onResume(AddAlarmActivity.java:147) at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1190) at android.app.Activity.performResume(Activity.java:5200) at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2930) at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2972) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2407) at android.app.ActivityThread.access0(ActivityThread.java:162) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1368) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5410) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) at dalvik.system.NativeStart.main(Native Method)

Answer 1

您是否忘记在 AndroidManifest.xml 中添加 Application class 的名字？

<manifest 
    ...
    <application
        name=".RemindMe"
    ...
    </application>
</manifest>

从设置首选项获取值时获取空指针异常

Getting null pointer exception when getting values from setting preference

android

nullpointerexception

android-application-class