java - 如何使用存储在 sharedPreference 中的字符串？

Question

我在“PlayersActivity”类中有这两种方法“saveCurrentPlayer”和“loadCurrentPlayer”来保存和加载字符串。

public void saveCurrentPlayer(){
        SharedPreferences preferences = getSharedPreferences("currentPlayer", Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = preferences.edit();
        editor.putString("currentPlayer",jugadorEliminar);
        editor.apply();
    }

    public String loadCurrentPlayer(){
        SharedPreferences preferences = getSharedPreferences("currentPlayer",Context.MODE_PRIVATE);
        String currentPlayer = preferences.getString("currentPlayer","");
        return currentPlayer;
    }

我尝试从另一个类“QuestionAnswerManagerActivity”中获取该字符串“currentPlayer”，但我强制关闭。

Toast.makeText(QuestionAnswerManagerActivity.this,playersActivity.loadCurrentPlayer(),Toast.LENGTH_SHORT).show();

这里是logcat：

2021-06-29 19:00:25.584 12936-12936/? I/actual.pregres: type=1400 audit(0.0:9796): avc: denied { sendto } for path="/dev/socket/logdw" scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=unix_dgram_socket permissive=1
2021-06-29 19:00:25.668 12936-12936/? I/zygote: Late-enabling -Xcheck:jni
2021-06-29 19:00:28.285 12936-12936/? W/zygote: Unexpected CPU variant for X86 using defaults: x86
2021-06-29 19:00:28.696 12936-12936/? I/JDWP: type=1400 audit(0.0:9801): avc: denied { connectto } for path=006A6477702D636F6E74726F6C scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=unix_stream_socket permissive=1
2021-06-29 19:00:28.840 12936-12936/? I/JDWP: type=1400 audit(0.0:9802): avc: denied { read write } for path="socket:[145879]" dev="sockfs" ino=145879 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=unix_stream_socket permissive=1
2021-06-29 19:00:31.308 12936-12936/? I/re-initialized>: type=1400 audit(0.0:9807): avc: denied { write } for path="socket:[145879]" dev="sockfs" ino=145879 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=unix_stream_socket permissive=1
2021-06-29 19:00:34.828 12936-12936/com.doctoractual.pregresp I/com.doctoractual.pregresp: type=1400 audit(0.0:9828): avc: denied { write } for comm=45474C20496E6974 name="property_service" dev="tmpfs" ino=174 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:property_socket:s0 tclass=sock_file permissive=1
2021-06-29 19:00:34.844 12936-12936/com.doctoractual.pregresp I/com.doctoractual.pregresp: type=1400 audit(0.0:9830): avc: denied { connectto } for comm=45474C20496E6974 path="/dev/socket/property_service" scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=unix_stream_socket permissive=1
2021-06-29 19:00:35.071 12936-12962/com.doctoractual.pregresp I/vndksupport: sphal namespace is not configured for this process. Loading /vendor/lib/egl/libGLES_emulation.so from the current namespace instead.
2021-06-29 19:00:35.231 12936-12962/com.doctoractual.pregresp I/vndksupport: sphal namespace is not configured for this process. Loading /vendor/lib/egl/libEGL_emulation.so from the current namespace instead.
2021-06-29 19:00:35.639 12936-12962/com.doctoractual.pregresp I/vndksupport: sphal namespace is not configured for this process. Loading /vendor/lib/egl/libGLESv1_CM_emulation.so from the current namespace instead.
2021-06-29 19:00:35.672 12936-12962/com.doctoractual.pregresp I/vndksupport: sphal namespace is not configured for this process. Loading /vendor/lib/egl/libGLESv2_emulation.so from the current namespace instead.
2021-06-29 19:00:36.080 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9835): avc: denied { write } for name="BASE_DATOS" dev="sdb3" ino=81843 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:system_data_file:s0:c512,c768 tclass=file permissive=1
2021-06-29 19:00:36.080 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9836): avc: denied { open } for path="/data/data/com.doctoractual.pregresp/databases/BASE_DATOS" dev="sdb3" ino=81843 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:system_data_file:s0:c512,c768 tclass=file permissive=1
2021-06-29 19:00:36.120 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9837): avc: denied { lock } for path="/data/data/com.doctoractual.pregresp/databases/BASE_DATOS" dev="sdb3" ino=81843 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:system_data_file:s0:c512,c768 tclass=file permissive=1
2021-06-29 19:00:36.173 12936-12970/com.doctoractual.pregresp D/OpenGLRenderer: HWUI GL Pipeline
2021-06-29 19:00:36.222 12936-12947/com.doctoractual.pregresp I/zygote: Background concurrent copying GC freed 4602(981KB) AllocSpace objects, 0(0B) LOS objects, 66% free, 780KB/2MB, paused 8.318ms total 54.936ms
2021-06-29 19:00:36.492 12936-12936/com.doctoractual.pregresp I/RenderThread: type=1400 audit(0.0:9844): avc: denied { write } for name="local_opengl" dev="tmpfs" ino=14777 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:socket_device:s0 tclass=sock_file permissive=1
2021-06-29 19:00:36.643 12936-12970/com.doctoractual.pregresp I/OpenGLRenderer: Initialized EGL, version 1.4
2021-06-29 19:00:36.643 12936-12970/com.doctoractual.pregresp D/OpenGLRenderer: Swap behavior 1
2021-06-29 19:00:36.647 12936-12970/com.doctoractual.pregresp W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
2021-06-29 19:00:36.647 12936-12970/com.doctoractual.pregresp D/OpenGLRenderer: Swap behavior 0
2021-06-29 19:00:36.677 12936-12970/com.doctoractual.pregresp D/EGL_emulation: eglCreateContext: 0xe7a051e0: maj 3 min 1 rcv 4
2021-06-29 19:00:36.760 12936-12970/com.doctoractual.pregresp I/vndksupport: sphal namespace is not configured for this process. Loading /vendor/lib/hw/gralloc.vbox86.so from the current namespace instead.
2021-06-29 19:00:36.778 12936-12970/com.doctoractual.pregresp E/eglCodecCommon: goldfish_dma_create_region: could not obtain fd to device! fd -1 errno=2
2021-06-29 19:00:37.177 12936-12936/com.doctoractual.pregresp I/Choreographer: Skipped 37 frames!  The application may be doing too much work on its main thread.
2021-06-29 19:00:38.704 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9870): avc: denied { open } for path="/dev/__properties__/u:object_r:serialno_prop:s0" dev="tmpfs" ino=136 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:serialno_prop:s0 tclass=file permissive=1
2021-06-29 19:00:38.704 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9871): avc: denied { getattr } for path="/dev/__properties__/u:object_r:serialno_prop:s0" dev="tmpfs" ino=136 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:serialno_prop:s0 tclass=file permissive=1
2021-06-29 19:00:41.640 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/os/PowerManager
2021-06-29 19:00:41.642 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/IntentService
2021-06-29 19:00:41.643 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/os/PowerManager$WakeLock
2021-06-29 19:00:41.649 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/Instrumentation
2021-06-29 19:00:41.650 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/JobSchedulerImpl
2021-06-29 19:00:41.651 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/job/JobServiceEngine$JobHandler
2021-06-29 19:00:41.663 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/ActivityThread
2021-06-29 19:00:41.666 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/os/Debug
2021-06-29 19:00:41.667 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/AlarmManager
2021-06-29 19:00:41.668 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/job/JobService
2021-06-29 19:00:41.669 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/PendingIntent
2021-06-29 19:00:41.673 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/location/LocationManager
2021-06-29 19:00:41.675 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: java/net/URL
2021-06-29 19:00:41.684 12936-12936/com.doctoractual.pregresp W/com.doctoractual.pregresp: Current dex file has more than one class in it. Calling RetransformClasses on this class might fail if no transformations are applied to it!
2021-06-29 19:00:41.687 12936-12936/com.doctoractual.pregresp I/chatty: uid=10071(u0_a71) com.doctoractual.pregresp identical 11 lines
2021-06-29 19:00:41.688 12936-12936/com.doctoractual.pregresp W/com.doctoractual.pregresp: Current dex file has more than one class in it. Calling RetransformClasses on this class might fail if no transformations are applied to it!
2021-06-29 19:00:42.597 12936-12936/com.doctoractual.pregresp W/zygote: Verification of void android.app.ActivityThread.handleStopBinderTrackingAndDump(android.os.ParcelFileDescriptor) took 108.552ms
2021-06-29 19:00:42.911 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/AlarmManager$ListenerWrapper
2021-06-29 19:00:42.912 12936-12936/com.doctoractual.pregresp W/com.doctoractual.pregresp: Changing class Landroid/app/AlarmManager$ListenerWrapper;
2021-06-29 19:00:42.914 12936-12936/com.doctoractual.pregresp W/com.doctoractual.pregresp: Dex file created by class-definition time transformation of Landroid/app/AlarmManager$ListenerWrapper; is not checked for all retransformation invariants.
2021-06-29 19:00:43.072 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/app/AlarmManager$ListenerWrapper
2021-06-29 19:00:43.074 12936-12936/com.doctoractual.pregresp W/zygote: Verification of void android.app.AlarmManager.setImpl(int, long, long, long, int, android.app.PendingIntent, android.app.AlarmManager$OnAlarmListener, java.lang.String, android.os.Handler, android.os.WorkSource, android.app.AlarmManager$AlarmClockInfo) took 321.983ms
2021-06-29 19:00:43.118 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Transformed class: android/location/LocationManager$ListenerTransport
2021-06-29 19:00:43.119 12936-12936/com.doctoractual.pregresp W/com.doctoractual.pregresp: Current dex file has more than one class in it. Calling RetransformClasses on this class might fail if no transformations are applied to it!
2021-06-29 19:00:43.202 12936-12936/com.doctoractual.pregresp W/zygote: Verification of void android.location.LocationManager.requestLocationUpdates(android.location.LocationRequest, android.location.LocationListener, android.os.Looper, android.app.PendingIntent) took 123.589ms
2021-06-29 19:00:43.234 12936-12936/com.doctoractual.pregresp V/StudioProfiler: Profiler initialization complete on agent.
2021-06-29 19:00:43.250 12936-13005/com.doctoractual.pregresp V/StudioProfiler: Acquiring Application for Events
2021-06-29 19:00:43.535 12936-12941/com.doctoractual.pregresp I/zygote: Do partial code cache collection, code=29KB, data=26KB
2021-06-29 19:00:43.536 12936-12941/com.doctoractual.pregresp I/zygote: After code cache collection, code=29KB, data=26KB
2021-06-29 19:00:43.536 12936-12941/com.doctoractual.pregresp I/zygote: Increasing code cache capacity to 128KB
2021-06-29 19:00:45.193 12936-12941/com.doctoractual.pregresp I/zygote: Do partial code cache collection, code=45KB, data=44KB
2021-06-29 19:00:45.195 12936-12941/com.doctoractual.pregresp I/zygote: After code cache collection, code=45KB, data=44KB
2021-06-29 19:00:45.205 12936-12941/com.doctoractual.pregresp I/zygote: Increasing code cache capacity to 256KB
2021-06-29 19:00:45.238 12936-12941/com.doctoractual.pregresp I/zygote: JIT allocated 71KB for compiled code of void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
2021-06-29 19:00:45.238 12936-12941/com.doctoractual.pregresp I/zygote: Compiler allocated 4MB to compile void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
2021-06-29 19:00:45.582 12936-12941/com.doctoractual.pregresp I/zygote: Do full code cache collection, code=124KB, data=66KB
2021-06-29 19:00:45.588 12936-12941/com.doctoractual.pregresp I/zygote: After code cache collection, code=107KB, data=42KB
2021-06-29 19:00:50.239 12936-12941/com.doctoractual.pregresp I/zygote: Do partial code cache collection, code=124KB, data=76KB
2021-06-29 19:00:50.236 12936-12936/com.doctoractual.pregresp I/com.doctoractual.pregresp: type=1400 audit(0.0:9879): avc: denied { sendto } for comm=4A69742074687265616420706F6F6C path="/dev/socket/logdw" scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:r:init:s0 tclass=unix_dgram_socket permissive=1
2021-06-29 19:00:50.250 12936-12941/com.doctoractual.pregresp I/zygote: After code cache collection, code=124KB, data=76KB
2021-06-29 19:00:50.250 12936-12941/com.doctoractual.pregresp I/zygote: Increasing code cache capacity to 512KB
2021-06-29 19:00:50.340 12936-12936/com.doctoractual.pregresp I/Choreographer: Skipped 52 frames!  The application may be doing too much work on its main thread.
2021-06-29 19:00:50.733 12936-12941/com.doctoractual.pregresp I/zygote: JIT allocated 56KB for compiled code of void android.view.View.<init>(android.content.Context, android.util.AttributeSet, int, int)
2021-06-29 19:00:50.932 12936-12941/com.doctoractual.pregresp I/zygote: Do full code cache collection, code=244KB, data=143KB
2021-06-29 19:00:50.933 12936-12941/com.doctoractual.pregresp I/zygote: After code cache collection, code=238KB, data=98KB
2021-06-29 19:00:52.121 12936-12941/com.doctoractual.pregresp I/zygote: Do partial code cache collection, code=243KB, data=108KB
2021-06-29 19:00:52.123 12936-12941/com.doctoractual.pregresp I/zygote: After code cache collection, code=243KB, data=108KB
2021-06-29 19:00:52.130 12936-12941/com.doctoractual.pregresp I/zygote: Increasing code cache capacity to 1024KB
2021-06-29 19:01:01.116 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9884): avc: denied { read } for name="databases" dev="sdb3" ino=81729 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:system_data_file:s0:c512,c768 tclass=dir permissive=1
2021-06-29 19:01:01.116 12936-12936/com.doctoractual.pregresp I/actual.pregresp: type=1400 audit(0.0:9885): avc: denied { open } for path="/data/data/com.doctoractual.pregresp/databases" dev="sdb3" ino=81729 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:system_data_file:s0:c512,c768 tclass=dir permissive=1
2021-06-29 19:01:01.142 12936-12936/com.doctoractual.pregresp D/AndroidRuntime: Shutting down VM
2021-06-29 19:01:01.144 12936-12936/com.doctoractual.pregresp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.doctoractual.pregresp, PID: 12936
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.doctoractual.pregresp.PlayersActivity.loadCurrentPlayer()' on a null object reference
        at com.doctoractual.pregresp.QuestionAnswerManagerActivity$4.onClick(QuestionAnswerManagerActivity.java:216)
        at android.view.View.performClick(View.java:6256)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
        at android.view.View$PerformClick.run(View.java:24697)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        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)

但是直接写文本没有问题，一切正常。

Toast.makeText(QuestionAnswerManagerActivity.this,"Jugador Luis",Toast.LENGTH_SHORT).show();

有人可以看到我做错了什么吗？提前致谢。

标签： javaandroidandroid-studiosharedpreferencesandroid-studio-4.2

Answer 1

您依赖于其他一些活动才能使用SharedPreferences. 在这种情况下，playersActivity是null您尝试使用它的时候。这是一个非常糟糕的 Android 开发设计，因为您不需要SharedPreferences任何依赖项，它可以完全独立。

解决方案：3个选项

1. 上交SharedPreferences方法Static。（例如loadCurrentPlayerinplayersActivity应该是Static）

2. 最佳实践：创建一个新的 Manager 类，负责应用程序的整个SharedPreferences使用（例如SharedPreferenceManager）。这个类是一个Singleton类，它被实例化ApplicationContext并具有与 CRUD 操作相关的所有方法SharedPreferences，在你的情况下saveCurrentPlayer和 loadCurrentPlayer. 由于管理器类是独立的，它不应该导致任何Lifecycle错误或NullPointer错误。

   由于附加示例代码会使我的答案混乱，我决定在这里引用别人的代码，这将教你如何实现它。

3. 如果您懒得关注 #2：您可以使用已经为您完成此操作的库：Pixplicity/EasyPrefs。

   • 像Class一样易于使用Manager✅</li>
   • 没有更多与SharedPreferences✅ 相关的错误</li>
   • 您可以随时改装到任何现有项目中✅</li>

如果您有任何问题，请告诉我。谢谢。