Marshmallow：无法从服务执行 Settings.System.canWrite(Context)

Question

我在后台有一个 NotificationListener 服务运行，当我执行 Settings.System.canWrite(Settings.java:3742)

时它会抛出异常

12-03 18:25:33.490    2754-2771/? W/System.err﹕ java.lang.SecurityException: uid 10057 does not have android.permission.UPDATE_APP_OPS_STATS.
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at android.os.Parcel.readException(Parcel.java:1599)
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at android.os.Parcel.readException(Parcel.java:1552)
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at com.android.internal.app.IAppOpsService$Stub$Proxy.checkOperation(IAppOpsService.java:327)
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at android.app.AppOpsManager.checkOpNoThrow(AppOpsManager.java:1536)
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at android.provider.Settings.isCallingPackageAllowedToPerformAppOpsProtectedOperation(Settings.java:8425)
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at android.provider.Settings.isCallingPackageAllowedToWriteSettings(Settings.java:8320)
12-03 18:25:33.490    2754-2771/? W/System.err﹕ at android.provider.Settings$System.canWrite(Settings.java:3742)

这是因为提供的 Context 是一项服务，因为从 activity 调用时不会发生这种情况。

Answer 1

这是一个 "bug"，尽管如您所说，预计不会从 NotificationListenerService 调用此方法。您应该从普通的 Activty 或 Service 调用它。我稍后会解释为什么。

根据你的踪迹，情况如下。

android.app.AppOpsManager.checkOpNoThrow(AppOpsManager.java:1536)

  /**
     * Like {@link #checkOp} but instead of throwing a {@link SecurityException} it
     * returns {@link #MODE_ERRORED}.
     * @hide
     */
    public int checkOpNoThrow(int op, int uid, String packageName) {
        try {
            return mService.checkOperation(op, uid, packageName); //1536
        } catch (RemoteException e) {
        }
        return MODE_ERRORED;
    }

虽然在 Parcel (android.os.Parcel.readException(Parcel.java:1599)) 中，它正在尝试捕获 RemoteException：

public final void readException(int code, String msg) {
    switch (code) {
        case EX_SECURITY:
            throw new SecurityException(msg); // 1599
        case EX_BAD_PARCELABLE:
            throw new BadParcelableException(msg);
        case EX_ILLEGAL_ARGUMENT:
            throw new IllegalArgumentException(msg);
        case EX_NULL_POINTER:
            throw new NullPointerException(msg);
        case EX_ILLEGAL_STATE:
            throw new IllegalStateException(msg);
        case EX_NETWORK_MAIN_THREAD:
            throw new NetworkOnMainThreadException();
        case EX_UNSUPPORTED_OPERATION:
            throw new UnsupportedOperationException(msg);
    }
    throw new RuntimeException("Unknown exception code: " + code
            + " msg " + msg);
}

它正在抛出一个SecurityException。

因为 SecurityException is NOT a RemoteException try-catch 未能捕捉到 checkOpNoThrow 中的异常，您得到了错误。

此外，如果您尝试使用应用程序的上下文（例如 this.getApplicationContext()）而不是侦听器服务的上下文，也会导致错误。这是由于 canWrite 正在检查调用者的 UID。通知侦听器具有与应用程序其他部分不同的 UID。

public static boolean canWrite(Context context) {
            int uid = Binder.getCallingUid(); 
            return isCallingPackageAllowedToWriteSettings(context, uid, getPackageNameForUid(
                    context, uid), false);
        }

编辑

此错误已在 AOSP issue tracker 上进行跟踪。

Marshmallow：无法从服务执行 Settings.System.canWrite(Context)

Marshmallow: Can't execute Settings.System.canWrite(Context) from a service

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