使用JSQMessage下载后很难让媒体替换占位符

Question

我正在使用JSQMessage，在正确下载之前显示媒体的占位符有点困难，然后用媒体替换它。只要把消息和媒体添加到服务器上，我就不能让它替换占位符。

目前，我有一个函数，它查询我的数据库，为消息提取一个对象数组，然后循环遍历，并对每个对象调用这个函数来输出并将其添加到我的消息线程。我很难弄清楚为什么"messageToAdd.isMediaMessage“部分没有在从服务器下载之后用实际媒体替换占位符。有谁知道我应该如何处理这个问题，以确保它用占位符添加消息，然后在媒体正确下载后进行替换？

- (void)addMessage:(PFObject *)object
{
    id<JSQMessageMediaData> messageMedia = nil;
    PFObject *user = object[@"messageSender"];
    [users addObject:user];
    NSString *name = @"";
    if(user[@"profileFName"] && user[@"profileLName"])
        name= [NSString stringWithFormat:@"%@ %@",user[@"profileFName"],user[@"profileLName"]];
    else
        name= [NSString stringWithFormat:@"%@ %@",user[@"consultantFName"],user[@"consultantLName"]];

    if([object[@"messageFileType"] isEqual: @"video"]){
        JSQVideoMediaItem *messageMedia = [[JSQVideoMediaItem alloc] init];
        messageMedia.fileURL = nil;
        messageMedia.isReadyToPlay = NO;
        messageToAdd = [JSQMessage messageWithSenderId:user.objectId displayName:name media:messageMedia];

    } else if ([object[@"messageFileType"] isEqual: @"image"]){
        JSQPhotoMediaItem *messageMedia = [[JSQPhotoMediaItem alloc] init];
        messageMedia.image = nil;
        messageToAdd = [JSQMessage messageWithSenderId:user.objectId displayName:name media:messageMedia];

    } else{
        messageToAdd= [[JSQMessage alloc] initWithSenderId:user.objectId senderDisplayName:name date:object[@"sendDate"] text:object[@"messageContent"]];
    }
    if(isLoadMore)
        [messages insertObject:messageToAdd atIndex:0];
    else
        [messages addObject:messageToAdd];

   // NOT TRIGGERING THESE AFTER MEDIA DOWNLOADED
    if (messageToAdd.isMediaMessage) {
        dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
            if ([object[@"messageFileType"] isEqual: @"image"]){
                [object[@"messageMedia"] getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error) {
                    if (!error) {
                        JSQPhotoMediaItem *photoItem = [[JSQPhotoMediaItem alloc] initWithImage:[UIImage imageWithData:imageData]];
                        ((JSQPhotoMediaItem *)messageMedia).image = [UIImage imageWithCGImage:photoItem.image.CGImage];
                        [self.collectionView reloadData];
                    }
                }];
            }
            else if([object[@"messageFileType"] isEqual: @"video"]){
                PFFile *videoFile = object[@"messageMedia"];
                NSURL *videoURL = [NSURL URLWithString:videoFile.url];
                ((JSQVideoMediaItem *)messageMedia).fileURL = videoURL;
                ((JSQVideoMediaItem *)messageMedia).isReadyToPlay = YES;
                [self.collectionView reloadData];
            }
            else {
                NSLog(@"%s error: unrecognized media item", __PRETTY_FUNCTION__);
            }
        });
    }
}

Answer 1

对于其他提出相同问题/问题的人，我通过查看项目NotificationChat：https://github.com/relatedcode/NotificationChat/blob/master/NotificationChat/Classes/Chat/ChatView.m，解决了它是如何工作的。它非常好地概述了JSQMessage平台的使用情况。

这是我修改的函数，这样你就可以看到成品了。

- (void)addMessage:(PFObject *)object
{
    PFObject *user = object[@"messageSender"];
    [users addObject:user];

    PFFile *mediaMessage = object[@"messageMedia"];

    NSString *name = @"";
    if(user[@"profileFName"] && user[@"profileLName"])
        name= [NSString stringWithFormat:@"%@ %@",user[@"profileFName"],user[@"profileLName"]];
    else
        name= [NSString stringWithFormat:@"%@ %@",user[@"consultantFName"],user[@"consultantLName"]];

    if([object[@"messageFileType"] isEqual: @"video"]){
        JSQVideoMediaItem *mediaItem = [[JSQVideoMediaItem alloc] initWithFileURL:[NSURL URLWithString:mediaMessage.url] isReadyToPlay:YES];
        mediaItem.appliesMediaViewMaskAsOutgoing = [user.objectId isEqualToString:self.senderId];
        messageToAdd = [[JSQMessage alloc] initWithSenderId:user.objectId senderDisplayName:name date:object.createdAt media:mediaItem];

    } else if ([object[@"messageFileType"] isEqual: @"image"]){
        JSQPhotoMediaItem *mediaItem = [[JSQPhotoMediaItem alloc] initWithImage:nil];
        mediaItem.appliesMediaViewMaskAsOutgoing = [user.objectId isEqualToString:self.senderId];
        messageToAdd = [[JSQMessage alloc] initWithSenderId:user.objectId senderDisplayName:name date:object.createdAt media:mediaItem];

        [mediaMessage getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error)
         {
             if (error == nil)
             {
                 mediaItem.image = [UIImage imageWithData:imageData];
                 [self.collectionView reloadData];
             }
         }];


    } else{
        messageToAdd= [[JSQMessage alloc] initWithSenderId:user.objectId senderDisplayName:name date:object[@"sendDate"] text:object[@"messageContent"]];
    }
    if(isLoadMore)
        [messages insertObject:messageToAdd atIndex:0];
    else
        [messages addObject:messageToAdd];

}

Answer 2

基于代码，我认为一个可能的原因是在后台线程上成功地和异步地下载数据后，在主(UI)线程上需要reloadData。