ios - UITableView 在移出屏幕之前不会完全填充单元格

Question

我正在使用 Parse 填充表格 View 中的单元格。每个单元格都包含用户名、用户图片和实际发布内容。当我运行该应用程序时，用户名和帖子内容会加载到每个单元格中。但是，直到将单元格移出屏幕然后再移回时，才会加载图片。这是我涉及查询的代码:

-(void)retrieveFromParse {

PFQuery *retrievePosts = [PFQuery queryWithClassName:@"Posts"];
[retrievePosts orderByDescending:@"createdAt"];
retrievePosts.cachePolicy = kPFCachePolicyCacheThenNetwork;
[retrievePosts findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {

    if (!error) {

        postsArray = [[NSArray alloc] initWithArray:objects];

         dispatch_async(dispatch_get_main_queue(), ^{
            [self.tableView reloadData];
        });
    }
         dispatch_async(dispatch_get_main_queue(), ^{
            [self.refreshControl endRefreshing];
    });
}];
}

这是表格 View 的代码:

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

postCell = [tableView dequeueReusableCellWithIdentifier:@"PostCellOne"];


if (postCell == nil ) {

    postCell = [[PostTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"PostCellOne"];


}

postCell.backgroundColor = [UIColor blackColor];
postCell.posterName.textColor = [UIColor whiteColor];
postCell.postContent.textColor = [UIColor whiteColor];

PFObject *postObject = [postsArray objectAtIndex:indexPath.row];
postCell.posterName.text = [postObject objectForKey:@"posterName"];
postCell.postContent.text = [postObject objectForKey:@"postContent"];
UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc]initWithFrame:postCell.posterImage.frame];
[postCell.posterImage addSubview:spinner];
spinner.color = [UIColor whiteColor];
[spinner startAnimating];
imageFile = [postObject objectForKey:@"posterPicture"];
[imageFile getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
    if (!error) {

        dispatch_async(dispatch_get_main_queue(), ^{
        [spinner removeFromSuperview];
        postCell.posterImage.image = [UIImage imageWithData:data];
        [tableView reloadInputViews];

        });
    }

    else {

        dispatch_async(dispatch_get_main_queue(), ^{
            [spinner removeFromSuperview];
        });
    }
}];

return postCell;

}

Answer 1

我正在使用 Parse 填充表格 View 中的单元格。每个单元格都包含用户名、用户图片和实际发布内容。当我运行该应用程序时，用户名和帖子内容会加载到每个单元格中。但是，直到将单元格移出屏幕然后再移回时，才会加载图片。这是我涉及查询的代码:

-(void)retrieveFromParse {

PFQuery *retrievePosts = [PFQuery queryWithClassName:@"Posts"];
[retrievePosts orderByDescending:@"createdAt"];
retrievePosts.cachePolicy = kPFCachePolicyCacheThenNetwork;
[retrievePosts findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {

    if (!error) {

        postsArray = [[NSArray alloc] initWithArray:objects];

         dispatch_async(dispatch_get_main_queue(), ^{
            [self.tableView reloadData];
        });
    }
         dispatch_async(dispatch_get_main_queue(), ^{
            [self.refreshControl endRefreshing];
    });
}];
}

这是表格 View 的代码:

 -(void)imageFromImageFile:(PFFile *)imageFile forCell:(PostTableViewCell *)cell
{
    PostTableViewCell *workingCell = cell;
    UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc]initWithFrame:postCell.posterImage.frame];
    [workingCell.posterImage addSubview:spinner];
    spinner.color = [UIColor whiteColor];
    [spinner startAnimating];
    [imageFile getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
        if (!error) {
            if(workingCell == cell){
                dispatch_async(dispatch_get_main_queue(), ^{
                    [spinner removeFromSuperview];
                    workingCell.posterImage.image = [UIImage imageWithData:data];
                    [workingCell setNeedsLayout];

                });
            }else{

                dispatch_async(dispatch_get_main_queue(), ^{
                    [spinner removeFromSuperview];
                });
            }
        }
    }];

}


-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    postCell = [tableView dequeueReusableCellWithIdentifier:@"PostCellOne"];


    if (postCell == nil ) {

        postCell = [[PostTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"PostCellOne"];


    }

    postCell.backgroundColor = [UIColor blackColor];
    postCell.posterName.textColor = [UIColor whiteColor];
    postCell.postContent.textColor = [UIColor whiteColor];

    PFObject *postObject = [postsArray objectAtIndex:indexPath.row];
    postCell.posterName.text = [postObject objectForKey:@"posterName"];
    postCell.postContent.text = [postObject objectForKey:@"postContent"];

    imageFile = [postObject objectForKey:@"posterPicture"];
    cell.posterImage.image = nil;
    [self imageFromImageFile:imageFile forCell:cell];

    return postCell;

}