android - 调用 ContentResolver.setSyncAutomatically android 时的空指针

Question

我想使用 android 同步适配器将本地应用程序数据库与远程服务器数据库同步。我遵循了开发者网站中提到的所有步骤，并仔细检查了每一件事。但是在我的 MainActivity oncreate 中执行以下行时我得到空指针:

mAccount = CreateSyncAccount(this);
ContentResolver.setSyncAutomatically(mAccount, AUTHORITY, true);

这是我的堆栈跟踪:

12-05 15:05:40.099: E/AndroidRuntime(13641): FATAL EXCEPTION: main
12-05 15:05:40.099: E/AndroidRuntime(13641): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mobinMahsaz.dortan/com.mobinMahsaz.dortan.MainActivity2}: java.lang.NullPointerException
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.os.Handler.dispatchMessage(Handler.java:99)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.os.Looper.loop(Looper.java:130)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.ActivityThread.main(ActivityThread.java:3687)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at java.lang.reflect.Method.invokeNative(Native Method)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at java.lang.reflect.Method.invoke(Method.java:507)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at dalvik.system.NativeStart.main(Native Method)
12-05 15:05:40.099: E/AndroidRuntime(13641): Caused by: java.lang.NullPointerException
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.os.Parcel.readException(Parcel.java:1328)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.os.Parcel.readException(Parcel.java:1276)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.content.IContentService$Stub$Proxy.setSyncAutomatically(IContentService.java:568)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.content.ContentResolver.setSyncAutomatically(ContentResolver.java:1047)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at com.mobinMahsaz.dortan.MainActivity2.onCreate(MainActivity2.java:283)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
12-05 15:05:40.099: E/AndroidRuntime(13641):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
12-05 15:05:40.099: E/AndroidRuntime(13641):    ... 11 more

我找不到任何说明此异常原因的文档。

编辑: 阅读 ContentResolver 文档后，我发现空指针是由 getcontentService() 引起的。

Answer 1

这对您来说可能有所不同，但对我来说，这是因为我有一个空的 mAccount 对象。我曾错误地假设如果 AccountManager.addAccountExplicitly 返回 false 则出现 fatal error ，因此从我的 CreateSyncAccount 函数返回一个 null 帐户在那种情况下。