Android: loading bitmap from local storage into app widget (RemoteViews)

Question

Until now I've been loading a bitmap into my RemoteViews directly using remoteViews.setImageViewBitmap(). It's working fine in general.

But a couple of users are having issues, and I think it is when loading in a bitmap that is very large. I cache the bitmap to local storage already anyway, so my idea is to use setImageViewUri() instead, as recommended elsewhere.

But I can't get it to work... I just get a blank widget. The following snippet illustrates what I'm doing (leaving out some the context but hopefully leaving enough)...

// Bitmap bmp is fetched from elsewhere... and then...

FileOutputStream fos = context.openFileOutput("img.png", Context.MODE_PRIVATE);
bmp.compress(Bitmap.CompressFormat.PNG, 100, fos);
fos.flush();
fos.close();

// ... later ...

// this works...
remoteViews.setImageViewBitmap(R.id.imageView, bmp);

// but this doesn't...
remoteViews.setImageViewUri(R.id.imageView, Uri.fromFile(new File(context.getFilesDir().getPath(), "img.png")));

EDIT

Trying to use FileProvider as suggested by CommonsWare below...

Manifest:

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

xml/file_paths.xml:

<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <files-path name="cache" path="."/>
</paths>

code:

File imagePath = new File(context.getFilesDir(), ".");
File newFile = new File(imagePath, "img.png"); // img.png created as above, in top level folder
remoteViews.setImageViewUri(R.id.imageView, FileProvider.getUriForFile(context, "com.xyz.fileprovider", newFile));

But still I'm left with a blank widget, as before, and without an error in the logcat.

Answer 1

Your app widget is being rendered by the home screen. The home screen cannot access internal storage of your app.

Instead, try using FileProvider to serve up files from internal storage, with a Uri supplied by FileProvider in your setImageViewUri() call.

UPDATE: I forgot about FileProvider's permission limitations. I do not know of a reliable way to grant permissions to the Uri to the home screen process via RemoteViews. Ideally, you would just allow the provider to be exported, but FileProvider does not support that.

Your options, then, are:

1. Write your own streaming ContentProvider, akin to this one, where the provider is exported, so anyone can consume the Uri values.

2. Put the file on external storage, instead of internal storage, then hope that the home screen has READ_EXTERNAL_STORAGE or WRITE_EXTERNAL_STORAGE permissions.

3. Ensure that your image is always fairly small, so your IPC transaction stays below the 1MB limit, and go with your original setImageViewBitmap() approach.

I apologize for having forgotten about FileProvider not allowing the provider to be exported.

Answer 2

This answer might be coming (quite) a bit late.

It is possible get this working by using a slightly modified FileProvider that allows the provider to be exported. Here is what you need to do:

1. Download the source code of FileProvider from here.
2. Copy the file to your project, e.g. to: com.xyz.fileprovider.FileProvider.java

3. Modify attachInfo(Context context, ProviderInfo info) so that it does not throw a SecurityException, if you declare your provider as exported:

   @Override
   public void attachInfo(Context context, ProviderInfo info) {
       super.attachInfo(context, info);
   
       // Sanity check our security
   
       // Do not throw an exception if the provider is exported
       /*
       if (info.exported) {
           throw new SecurityException("Provider must not be exported");
       }
       */
       if (!info.grantUriPermissions) {
           throw new SecurityException("Provider must grant uri permissions");
       }
   
       mStrategy = getPathStrategy(context, info.authority);
   }
   

4. Update your manifest file, so that it references your modified FileProvider and set android:exported to true:

   <provider>
       android:name="com.xyz.fileprovider.FileProvider"
       android:authorities="com.xyz.fileprovider"
       android:exported="true"
       android:grantUriPermissions="true">
       <meta-data
           android:name="android.support.FILE_PROVIDER_PATHS"
           android:resource="@xml/file_paths" />
   </provider>
   

5. Update your code, so that you are using com.xyz.fileprovider.FileProvider instead of android.support.v4.content.FileProvider:

   // Bitmap bmp is fetched from elsewhere... and then...
   
   FileOutputStream fos = context.openFileOutput("img.png", Context.MODE_PRIVATE);
   bmp.compress(Bitmap.CompressFormat.PNG, 100, fos);
   fos.flush();
   fos.close();
   
   // ... later ...
   
   // this should work...
   File imagePath = new File(context.getFilesDir(), ".");
   File newFile = new File(imagePath, "img.png"); // img.png created as above, in top level folder
   
   remoteViews.setImageViewUri(R.id.imageView, Uri.parse("")); // this is necessary, without it the launcher is going to cache the Uri we set on the next line and effectively update the widget's image view just once!!!
   remoteViews.setImageViewUri(R.id.imageView, com.xyz.fileprovider.FileProvider.getUriForFile(context, "com.xyz.fileprovider", newFile));
   

Answer 3

Method remoteViews.setImageViewUri additionally has limitation of bitmap size for ImageView (approximately 1-2 Mb ). So you will gets errors or widget will be transparent.

So remoteViews.setImageViewBitmap() is good practice, but you have too create procedure with BitmapFactory.Options inSampleSize and try to bounds bitmap to the screen size and catch OutOfMemoryError.

Answer 4

Came across this today but figured that granting access to any launcher app is a smaller security hole than exporting the whole provider :)

So right before setting the uri to the remote views I'm now granting access to the URI to each installed home screen:

protected void bindTeaserImage(Context context, final RemoteViews remoteViews, final TeaserInfo teaserInfo) {
    final Uri teaserImageUri = getTeaserImageUri(teaserInfo); // generates a content: URI for my FileProvider
    grantUriAccessToWidget(context, teaserImageUri);
    remoteViews.setImageViewUri(R.id.teaser_image, teaserImageUri);
}

protected void grantUriAccessToWidget(Context context, Uri uri) {
    Intent intent= new Intent(Intent.ACTION_MAIN);
    intent.addCategory(Intent.CATEGORY_HOME);
    List<ResolveInfo> resInfoList = context.getPackageManager().queryIntentActivities(intent, PackageManager.MATCH_DEFAULT_ONLY);
    for (ResolveInfo resolveInfo : resInfoList) {
        String packageName = resolveInfo.activityInfo.packageName;
        context.grantUriPermission(packageName, uri, Intent.FLAG_GRANT_READ_URI_PERMISSION);
    }
}