【发布时间】：2014-06-03 09:52:24
【问题描述】：
我正在尝试使用系统首选项存储一些变量。我尝试了一些教程，但应用程序不断崩溃。有人可以帮助我。我也根据this尝试过。还有这段代码：
SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
Editor editor = sharedPreferences.edit();
这是 logcat 输出：
06-03 15:17:08.600: D/BstCommandProcessor-Application(908): Application crash has been observed.
06-03 15:17:08.600: I/Process(10216): Sending signal. PID: 10216 SIG: 9
06-03 15:17:08.600: D/AndroidRuntime(10216): procName from cmdline: com.example.flash4
06-03 15:17:08.600: E/AndroidRuntime(10216): in writeCrashedAppName, pkgName :com.example.flash4
06-03 15:17:08.600: D/AndroidRuntime(10216): file written successfully with content: com.example.flash4 StringBuffer : ;com.example.flash4
06-03 15:17:08.600: E/AndroidRuntime(10216): FATAL EXCEPTION: main
06-03 15:17:08.600: E/AndroidRuntime(10216): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.flash4/com.example.flash4.MainActivity}: java.lang.NullPointerException
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.os.Handler.dispatchMessage(Handler.java:99)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.os.Looper.loop(Looper.java:137)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.ActivityThread.main(ActivityThread.java:4424)
06-03 15:17:08.600: E/AndroidRuntime(10216): at java.lang.reflect.Method.invokeNative(Native Method)
06-03 15:17:08.600: E/AndroidRuntime(10216): at java.lang.reflect.Method.invoke(Method.java:511)
06-03 15:17:08.600: E/AndroidRuntime(10216): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
06-03 15:17:08.600: E/AndroidRuntime(10216): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:592)
06-03 15:17:08.600: E/AndroidRuntime(10216): at dalvik.system.NativeStart.main(Native Method)
06-03 15:17:08.600: E/AndroidRuntime(10216): Caused by: java.lang.NullPointerException
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:127)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:371)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:366)
06-03 15:17:08.600: E/AndroidRuntime(10216): at com.example.flash4.MainActivity.<init>(MainActivity.java:71)
06-03 15:17:08.600: E/AndroidRuntime(10216): at java.lang.Class.newInstanceImpl(Native Method)
06-03 15:17:08.600: E/AndroidRuntime(10216): at java.lang.Class.newInstance(Class.java:1319)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.Instrumentation.newActivity(Instrumentation.java:1025)
06-03 15:17:08.600: E/AndroidRuntime(10216): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871)
06-03 15:17:08.600: E/AndroidRuntime(10216): ... 11 more
06-03 15:17:08.690: I/ActivityManager(610): Process com.example.flash4 (pid 10216) has died.
06-03 15:17:08.690: W/ActivityManager(610): Force removing ActivityRecord{b335c7d8 com.example.flash4/.MainActivity}: app died, no saved state
【问题讨论】：
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你需要哪个代码。错误出现在第 71 行，即我上面给出的代码。
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在你的
Activity中试试这个SharedPreferences sharedPreferences =getDefaultSharedPreferences(this); -
您是否重命名了项目中的任何内容？如果是，请确保您在 ande clean 项目中没有错误
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@Simple Plan: 那行给了我这个错误：方法 getDefaultSharedPreferences(MainActivity) 未定义 MainActivity 类型
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确保您提供的上下文是有效的。为了获得默认的 SharedPreferences，您需要有一个上下文。这是必需的，因为 getDefaultSharedPreferences() 将调用 getSharedPreferences(String name, mode)，其中 "name" 是这样获取的，context.getPackageName() + "_preferences";您还可以制作自定义文件，例如： SharedPreferences sharedPreferences = context.getSharedPreferences("sp_file_name", Context.MODE_PRIVATE);