Xamarin.Forms Android FileProvider: GrantWriteUriPermission not always working

问题:

I want to edit files from the internal storage of my Xamarin.Forms Android app in third party apps, for example fill out form elements in a PDF file or edit a .docx file.

With my implementation the file gets correctly opened in the external app, but in certain apps it is opened read-only. Adobe Acrobat and Microsoft Word open the files read-only, while other apps like Google Docs are able to write back into the file. (I am using Microsoft Word with a valid Office365 subscription).

My FileProvider in the AndroidManifest.xml:

<provider android:name="android.support.v4.content.FileProvider"            android:authorities="xamarintestapp.xamarintestapp.fileprovider"            android:grantUriPermissions="true"            android:exported="false">     <meta-data android:name="android.support.FILE_PROVIDER_PATHS"                     android:resource="@xml/filepaths" /> </provider> 

filepaths.xml:

Via the Xamarin.Forms DependencyService I am starting a Activity and pass the content uri to launch the external app:

public void OpenFile(string fileName) {     string auth = "xamarintestapp.xamarintestapp.fileprovider";     string mimeType = Android.Webkit.MimeTypeMap.Singleton.GetMimeTypeFromExtension(Android.Webkit.MimeTypeMap.GetFileExtensionFromUrl(fileName.ToLower()));     if (mimeType == null)         mimeType = "*/*";      var file = new Java.IO.File(Path.Combine(Forms.Context.FilesDir.Path, fileName));     Android.Net.Uri uri = FileProvider.GetUriForFile(Forms.Context, auth, file);      Intent intent = new Intent(Intent.ActionView);     intent.SetDataAndType(uri, mimeType);     intent.AddFlags(ActivityFlags.GrantReadUriPermission | ActivityFlags.GrantWriteUriPermission);     intent.AddFlags(ActivityFlags.NewTask | ActivityFlags.NoHistory);      // Trying to allow writing to the external app ...     var resInfoList = Forms.Context.PackageManager.QueryIntentActivities(intent, PackageInfoFlags.MatchDefaultOnly);     foreach (var resolveInfo in resInfoList)     {         var packageName = resolveInfo.ActivityInfo.PackageName;         Forms.Context.GrantUriPermission(packageName, uri, ActivityFlags.GrantWriteUriPermission | ActivityFlags.GrantPrefixUriPermission | ActivityFlags.GrantReadUriPermission);     }      Forms.Context.StartActivity(intent); } 

Am I doing something wrong or is this simply not possible?

回答1:

After further investigation I can confirm that this seems to be an issue of the app receiving my intent (e.g. Microsoft Word).

When I start a EDIT intent instead of a VIEW intent as in

Intent intent = new Intent(Intent.ActionEdit); 

the file is opened with write access in certain apps (xodo pdf, google docs) but read-only in other apps (Adobe PDF Reader, Microsoft Word) so I'm assuming these apps do not implement receiving an edit intent correctly.

文章来源: Xamarin.Forms Android FileProvider: GrantWriteUriPermission not always working