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

Question

我有一个在后台运行的NotificationListener服务,当我执行Settings.System.canWrite(Settings.java:3742)时会抛出异常

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是一种服务,因为从活动调用时不会发生这种情况.

Answer 1

这是一个“错误”，尽管正如您所说，预计不会从NotificationListenerService. 您应该从普通的Activty或来调用它Service。稍后我会解释原因。

根据你的痕迹，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;
    }

在这里，它试图捕获RemoteException虽然在Parcel（android.os.Parcel.readException(Parcel.java:1599)）中发生的情况：

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.

由于SecurityException不是RemoteException， try-catch 无法捕获 中的异常，checkOpNoThrow并且您会收到错误。

更重要的是，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's 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

此错误在AOSP 问题跟踪器上进行跟踪。