/// <summary>
/// 打开包含给定帖子的给定索引处的图片的数据流。
/// </summary>
/// <param name="dataFacade"></param>
/// <param name="postId">帖子 ID</param>
/// <param name="imageIndex">图像索引</param>
/// <returns></returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="dataFacade"/>为null
/// </exception>
/// <exception cref="ArgumentOutOfRangeException">
/// <paramref name="imageIndex"/>小于0 或 大于等于9
/// </exception>
public static async Task <Stream> OpenPostImage(this IDataFacade dataFacade, int postId, int imageIndex)
{
if (dataFacade == null)
{
throw new ArgumentNullException(nameof(dataFacade));
}
if (imageIndex < 0 || imageIndex >= 9)
{
throw new ArgumentOutOfRangeException(nameof(imageIndex));
}
var(indexEntity, contentEntity) = await FindPost(dataFacade, postId);
if (imageIndex >= contentEntity.ImageIds.Length)
{
return(null);
}
var imageId = contentEntity.ImageIds[imageIndex];
if (imageId == null)
{
return(null);
}
return(await dataFacade.OpenImage(imageId.Value));
}