DocumentsContract.java 文件源码

/**
 * Return thumbnail representing the document at the given URI. Callers are
 * responsible for their own in-memory caching.
 *
 * @param documentUri document to return thumbnail for, which must have
 *            {@link Document#FLAG_SUPPORTS_THUMBNAIL} set.
 * @param size optimal thumbnail size desired. A provider may return a
 *            thumbnail of a different size, but never more than double the
 *            requested size.
 * @param signal signal used to indicate if caller is no longer interested
 *            in the thumbnail.
 * @return decoded thumbnail, or {@code null} if problem was encountered.
 * @see DocumentsProvider#openDocumentThumbnail(String, Point,
 *      CancellationSignal)
 */
public static Bitmap getDocumentThumbnail(
        ContentResolver resolver, Uri documentUri, Point size, CancellationSignal signal) {
    final ContentProviderClient client = ContentProviderClientCompat.acquireUnstableContentProviderClient(resolver, 
            documentUri.getAuthority());
    try {
        if(UsbStorageProvider.AUTHORITY.equals(documentUri.getAuthority())) {
            return ImageUtils.getThumbnail(resolver, documentUri, size.x, size.y);
        }
        return getDocumentThumbnails(client, documentUri, size, signal);
    } catch (Exception e) {
        if (!(e instanceof OperationCanceledException)) {
            Log.w(TAG, "Failed to load thumbnail for " + documentUri + ": " + e);
        }
        return null;
    } finally {
        ContentProviderClientCompat.releaseQuietly(client);
    }
}