ios - 有没有办法在方法完成后运行代码？

Question

我想在方法完成后开始代码。我有一个UICollectionView，它从服务器加载图像数组，然后将这些图像添加到我创建的单元格中的 ImageView 中，以更好地解释这里是我的代码:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *cellID = @"cellID";
    insightCell *myCell = (insightCell *)[collectionView dequeueReusableCellWithReuseIdentifier:cellID forIndexPath:indexPath];
    myCell.tag = [[[objectiveGov n_insights] objectAtIndex:indexPath.item]integerValue];
    imgTag = ((UICollectionView *)myCell).tag;
//This is the Method I want to run "ObjectiveGov is the NSObject which has my Method inside "arrayImages" which is separate to the view controller this UICollectionView is in.
    [objectiveGov arrayImages];

//Possible if statement here, that records when the method above is finished.
    myCell.insightImageView.image = [theInsightImage objectAtIndex:indexPath.item];
            return myCell;
        }

因此，一旦方法[objectiveGov arrayImages];完成，我希望它运行myCell.insightImageView.image。有办法做到这一点吗？我尝试创建一个在方法末尾发布的 NSNotificationCenter，但这不起作用，因为 UICollectionViewCell 方法在分配 UICollectionView 时启动。有任何想法吗？谢谢!

编辑ArrayImages方法代码:

+(void)arrayImages
{
    [[NSNotificationCenter defaultCenter] postNotificationName:@"postArrayImages" object:nil];
    [[NSUserDefaults standardUserDefaults] synchronize];

    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@/api/insights/get/",URL_ROOT]];
    AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
    NSString *imageString = [NSString stringWithFormat:@"%d",[viewInsightViewController imgTag]];
    NSURLRequest *request = [httpClient requestWithMethod:@"GET" path:imageString parameters:nil];
    AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {

        NSDictionary *dictionInsight = [JSON valueForKey:@"results"];
        NSArray *insightArray = [dictionInsight valueForKey:@"images"];
        NSString *fileName = [dictionInsight valueForKey:@"filename"];
        if (fileName == (id) [NSNull null])
        {
//URL incase server file doesnt contain image.
            nineArray = [NSString stringWithFormat:@"http://url.co.uk/images/logo.png"];
        }else {
            nineArray = [insightArray valueForKey:@"96"];
        }
        insightURL = [NSURL URLWithString:nineArray];

         if (insightURL != nil) {
        NSURLRequest *requestImage = [NSURLRequest requestWithURL:insightURL];
        AFImageRequestOperation *imageOperation = [AFImageRequestOperation imageRequestOperationWithRequest:requestImage imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image)
                                                   { 
                                                       if (requestImage != nil) {
                                                           insightImages = image;
                                                           [arrayOfImages addObject:insightImages];                                                      
 }

                                                   } failure:nil];
        [imageOperation start];
         }

Answer 1

使用 block 对于这种情况来说是完美的。将数组图像方法更改为类似这样的方法，以便在 afnetworking 完成时调用传回加载图像的 block 。

+ (void)arrayImagesWithCompletionBlock:(void(^)(UIImage *image))completionBlock {
....
       if (insightURL != nil) {
            NSURLRequest *requestImage = [NSURLRequest requestWithURL:insightURL];
            AFImageRequestOperation *imageOperation = [AFImageRequestOperation imageRequestOperationWithRequest:requestImage imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                    if (requestImage != nil) {

                       insightImages = image;
                       [arrayOfImages addObject:insightImages];

                       // Call the completion block here once we have the loaded image
                       completionBlock(image);
                    }];

               } failure:nil];

            [imageOperation start];
        }
....
}

并在 cellForIndexPath 中这样调用它:

[objectiveGov arrayImagesWithCompletionBlock:^(UIImage *loadedImage) {
    myCell.insightImageView.image = loadedImage;    
}];

最后一件事，您在实际想要执行 objectForKey 的地方调用 valueForKey。 (valueForKey 将获取对象的属性值与您想要的字典方法的比较，请搜索“键值编码”以获取更多信息)。