How to get android lock screen wallpaper?

Question

I use the code below to retrieve the android lock screen wallpaper on an android 8.1 phone:

WallpaperManager manager = WallpaperManager.getInstance(getActivity());
ParcelFileDescriptor pfd = manager.getWallpaperFile(WallpaperManager.FLAG_LOCK);
if (pfd == null) // pfd is always null for FLAG_LOCK, why?
    return;
Bitmap lockScreenWallpaper = BitmapFactory.decodeFileDescriptor(pfd.getFileDescriptor());
// ...

I have granted the READ_EXTERNAL_STORAGE permission and set a lock screen wallpaper beforehand.

I run the demo on a real phone, and found the pfd is always null for FLAG_LOCK, so I cannot get the lock screen wallpaper. Please help fix the problem, thanks.

Answer 1

I find the answer myself, I hope it can help others with the same question.

The official docs for getWallpaperFile says: If no lock-specific wallpaper has been configured for the given user, then this method will return null when requesting FLAG_LOCK rather than returning the system wallpaper's image file.

The description is vague, at least not clear enough, what does it mean? If you set a photo as both lock screen and home screen wallpaper, the two share the same file, then by calling

ParcelFileDescriptor pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_LOCK);

pfd will always be null, then you should get the lock screen wallpaper this way:

if (pfd == null)
    pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_SYSTEM);

you will get the non-null pfd. This is the case no lock-specific wallpaper has been configured.

On the contrary, lock-specific wallpaper has been configured if you set a photo as lock screen wallpaper directly, wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_SYSTEM) will return a non-null value.

So this is the code I use to retrieve the lock screen wallpaper:

/**
 * please check permission outside
 * @return Bitmap or Drawable
 */
public static Object getLockScreenWallpaper(Context context)
{
    WallpaperManager wallpaperManager = WallpaperManager.getInstance(context);
    if (Build.VERSION.SDK_INT >= 24)
    {
        ParcelFileDescriptor pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_LOCK);
        if (pfd == null)
            pfd = wallpaperManager.getWallpaperFile(WallpaperManager.FLAG_SYSTEM);
        if (pfd != null)
        {
            final Bitmap result = BitmapFactory.decodeFileDescriptor(pfd.getFileDescriptor());

            try
            {
                pfd.close();
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }

            return result;
        }
    }
    return wallpaperManager.getDrawable();
}

Don't forget to add READ_EXTERNAL_STORAGE in the manifest file and grant it outside.