Android11分区存储，图片分页加载适配

Android11正式版已经推出，我们将targetSdkVersion和compileSdkVersion都升级到30，并升级pixel4到Android11，发现分区存储读取图片失败。经过分析，发现问题如下：

context.contentResolver.query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI
                        , getPhotoProjectionSQL(bucketId)
                        , getMediaSelectionSQL(true, bucketId)
                        , null
                        , getMediaOrderBySQL(start, count + 20))
 
 
private fun getMediaOrderBySQL(start: Int = 0, count: Int = Int.MAX_VALUE) = "${MediaStore.MediaColumns.DATE_MODIFIED} DESC limit $count offset $start"

getMediaOrderBySQL()方法抛出异常：

WechatIMG1.jpeg

从log上看，是SQL语句出了问题，指向limit。经过各种尝试，发现sortOrder这个参数在Android11中只支持排序方式，不再支持limit等查询限制。但是通常我们加载相册图片/视频等是需要分页的，从官方文档中没有找到相应的例子说明。在阅读query()方法的源码，我们发现query()的实现如下：

public final @Nullable Cursor query(@RequiresPermission.Read @NonNull Uri uri,
        @Nullable String[] projection, @Nullable String selection,
        @Nullable String[] selectionArgs, @Nullable String sortOrder,
        @Nullable CancellationSignal cancellationSignal) {
    Bundle queryArgs = createSqlQueryBundle(selection, selectionArgs, sortOrder);
    return query(uri, projection, queryArgs, cancellationSignal);
}

将selection, selectionArgs, sortOrder封装成一个Bundle对象传给query()方法：

* @param uri The URI, using the content:// scheme, for the content to
 *         retrieve.
 * @param projection A list of which columns to return. Passing null will
 *         return all columns, which is inefficient.
 * @param queryArgs A Bundle containing additional information necessary for
 *            the operation. Arguments may include SQL style arguments, such
 *            as {@link ContentResolver#QUERY_ARG_SQL_LIMIT}, but note that
 *            the documentation for each individual provider will indicate
 *            which arguments they support.
 * @param cancellationSignal A signal to cancel the operation in progress, or null if none.
 * If the operation is canceled, then {@link OperationCanceledException} will be thrown
 * when the query is executed.
 * @return A Cursor object, which is positioned before the first entry. May return
 *         <code>null</code> if the underlying content provider returns <code>null</code>,
 *         or if it crashes.
 * @see Cursor
 */
@Override
public final @Nullable Cursor query(final @RequiresPermission.Read @NonNull Uri uri,
        @Nullable String[] projection, @Nullable Bundle queryArgs,
        @Nullable CancellationSignal cancellationSignal)

不看这段代码具体的实现，主要是看注释对于queryArgs这个参数的说明：

 * @param queryArgs A Bundle containing additional information necessary for
 *            the operation. Arguments may include SQL style arguments, such
 *            as {@link ContentResolver#QUERY_ARG_SQL_LIMIT}, but note that
 *            the documentation for each individual provider will indicate
 *            which arguments they support.

such as这句：such as {@link ContentResolver#QUERY_ARG_SQL_LIMIT}，猜测QUERY_ARG_SQL_LIMIT可能跟我们需要的limit有关。往回看Bundle的创建过程：

Bundle queryArgs = createSqlQueryBundle(selection, selectionArgs, sortOrder);
 
public static @Nullable Bundle createSqlQueryBundle(
            @Nullable String selection,
            @Nullable String[] selectionArgs,
            @Nullable String sortOrder) {
 
        if (selection == null && selectionArgs == null && sortOrder == null) {
            return null;
        }
 
        Bundle queryArgs = new Bundle();
        if (selection != null) {
            queryArgs.putString(QUERY_ARG_SQL_SELECTION, selection);
        }
        if (selectionArgs != null) {
            queryArgs.putStringArray(QUERY_ARG_SQL_SELECTION_ARGS, selectionArgs);
        }
        if (sortOrder != null) {
            queryArgs.putString(QUERY_ARG_SQL_SORT_ORDER, sortOrder);
        }
        return queryArgs;
    }

QUERY_ARG_SQL_SELECTION，QUERY_ARG_SQL_SELECTION_ARGS，QUERY_ARG_SQL_SORT_ORDER都是我们的传参。猜测是否可以为queryArgs增加QUERY_ARG_SQL_LIMIT来实现limit呢？于是把createSqlQueryBundle()方法copy到我们的代码中，并增加QUERY_ARG_SQL_LIMIT，如下：

val bundle = createSqlQueryBundle(getMediaSelectionSQL(true, bucketId)
                        , null
                        , getMediaOrderBySQLNoLimit(), count + 20, start)
                context.contentResolver.query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI
                        , getPhotoProjectionSQL(bucketId)
                        , bundle
                        , null)
 
 
private fun createSqlQueryBundle(
            selection: String?,
            selectionArgs: Array<String?>?,
            sortOrder: String?, limitCount: Int = 0, offset: Int = 0): Bundle? {
        if (selection == null && selectionArgs == null && sortOrder == null) {
            return null
        }
        val queryArgs = Bundle()
        if (selection != null) {
            queryArgs.putString(ContentResolver.QUERY_ARG_SQL_SELECTION, selection)
        }
        if (selectionArgs != null) {
            queryArgs.putStringArray(ContentResolver.QUERY_ARG_SQL_SELECTION_ARGS, selectionArgs)
        }
        if (sortOrder != null) {
            queryArgs.putString(ContentResolver.QUERY_ARG_SQL_SORT_ORDER, sortOrder)
        }
        queryArgs.putString(ContentResolver.QUERY_ARG_SQL_LIMIT, "$limitCount offset $offset")
        return queryArgs
    }

调用如下：

val bundle = createSqlQueryBundle(getMediaSelectionSQL(false, bucketId)
                        , null
                        , getMediaOrderBySQLNoLimit(), count + 20, start)
                context.contentResolver.query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI
                        , getVideoProjectionSQL(bucketId)
                        , bundle
                        , null)

经测试分页加载成功。