android - 当无法解析具有 "downloads"权限的内容提供程序时，PackageInstaller 崩溃

Question

作为一些背景知识，我正在 Xamarin 中为一家企业编写一个 Android 应用程序，它应该能够自行更新，而不是通过 Play 商店进行更新。特别是有一种设备无法自行更新，我不明白为什么。

更新的代码如下所示:

            try
            {
                var intent = new Intent(Intent.ActionInstallPackage);
                intent.SetFlags(ActivityFlags.NewTask);
                var file = new Java.IO.File(Android.OS.Environment.ExternalStorageDirectory.Path + "/com.mycompany.appname.apk");
                var uri = FileProvider.GetUriForFile(this, "com.mycompany.appname.update_file_provider", file);
                GrantUriPermission("com.google.android.packageinstaller", uri, ActivityFlags.GrantReadUriPermission);
                intent.SetDataAndType(uri, "application/vnd.android.package-archive");
                var pendingIntent = PendingIntent.GetActivity(this, 0, intent, 0);
                var notification = GetNotificationBuilder(installedVersion, latestVersion, this)
                    .SetContentText("Download complete.")
                    .AddAction(new NotificationCompat.Action(Resource.Drawable.ic_note_add_black_24dp, "Install", pendingIntent))
                    .SetAutoCancel(true)
                    .Build();
                NotificationManagerCompat.From(this).Notify(NotificationId, notification);
                StopSelf();
            }
            catch (Exception e)
            {
                var notification = GetNotificationBuilder(installedVersion, latestVersion, this)
                    .SetContentText("Failed to install update: " + e.Message)
                    .SetAutoCancel(true)
                    .Build();
                NotificationManagerCompat.From(this).Notify(NotificationId, notification);
                StopSelf();
                return;
            }

当它运行时，我收到一条消息:“PackageInstaller 已停止。”堆栈跟踪显示这是由于软件包安装程序应用程序中的 NPE 造成的:

12-02 17:37:17.153  4897  4897 E AndroidRuntime: FATAL EXCEPTION: main
12-02 17:37:17.153  4897  4897 E AndroidRuntime: Process: com.google.android.packageinstaller, PID: 4897
12-02 17:37:17.153  4897  4897 E AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.google.android.packageinstaller/com.android.packageinstaller.InstallStart}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.ComponentName android.content.pm.ComponentInfo.getComponentName()' on a null object reference
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2785)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2863)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.ActivityThread.-wrap11(Unknown Source:0)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1596)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:106)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:164)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:6537)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:465)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
12-02 17:37:17.153  4897  4897 E AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.ComponentName android.content.pm.ComponentInfo.getComponentName()' on a null object reference
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at com.android.packageinstaller.InstallStart.isSystemDownloadsProvider(InstallStart.java:230)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at com.android.packageinstaller.InstallStart.getOriginatingUid(InstallStart.java:222)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at com.android.packageinstaller.InstallStart.onCreate(InstallStart.java:73)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.Activity.performCreate(Activity.java:7023)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.Activity.performCreate(Activity.java:7014)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1215)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2738)
12-02 17:37:17.153  4897  4897 E AndroidRuntime:        ... 9 more

郑重声明:此特定设备运行的是 Android 8.1。我已经在运行 Android 8.0、Android 10 和 Android 7 的其他设备上对此进行了测试，没有出现任何问题，但我没有任何其他具有该确切 Android 版本的设备可供测试。

编辑我意识到我应该对标题进行更多解释。我实际上已经研究过 source code for the PackageInstaller app ，在堆栈跟踪出现的位置周围，看来这一行是此 NPE 的原因:

final String downloadProviderPackage = getPackageManager().resolveContentProvider(
                DOWNLOADS_AUTHORITY, 0).getComponentName().getPackageName();

DOWNLOADS_AUTHORITY 是一个值为 "downloads" 的常量字符串，对 resolveContentProvider() 的调用返回 null。目前尚不清楚为什么此特定设备会出现这种情况，而其他设备则不会，或者如何修复它。

Answer 1

问题原来是下载管理器已被禁用。这似乎是仅在 android 8.0 和 8.1 中存在的问题。我仍然不确定它是如何开始被禁用的，但我的解决方案是使用 blackapps 推荐的空检查，并包含一个提示，让用户在检测到这种情况时重新启用它。