如何运行活动指示器，直到下载完映像为止

Question

我有一个UITableView，每个cell中都有一个图像。当我单击cell时，将下载图像。我要显示活动指示器，直到未下载图像为止。

这里是代码

TableView代码

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
UITapGestureRecognizer *tap=[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(PicturePerformGesture:)];
[cell.oMessageImg setUserInteractionEnabled:YES];
}

PicturePerformGesture代码

UIActivityIndicatorView  *iActivity=[[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[iActivity startAnimating];
VideoData =[NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:videoUrl] returningResponse:nil error:nil];
[VideoData writeToFile:fullPath atomically:true];
 [iActivity stopAnimating];

下载前下载时

Answer 1

[此时创建图像单元时，需要检查是否下载了图像，如果是，可以点击图像，否则在其上启动ActivityIndi​​cator，并且在完成图像下载时，可以停止ActivityIndi​​cator以获得最佳图像下载体验，请使用SDWebImage 3rd party库并获得所有图像状态，如下所述。

使用补全框：

// Here we use the new provided sd_setImageWithURL: method to load the web image
[cell.imageView sd_setImageWithURL:[NSURL URLWithString:@"http://www.example.com/path/to/image.jpg"]
                      placeholderImage:[UIImage imageNamed:@"placeholder.png"]
                             completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
                                ... completion code here ...

   // Add Your Stop Activity Code here.

}];

获得图像下载进度的另一种方法，使用下面的代码块：

SDWebImageDownloader *downloader = [SDWebImageDownloader sharedDownloader];
[downloader downloadImageWithURL:imageURL
                         options:0
                        progress:^(NSInteger receivedSize, NSInteger expectedSize) {
                            // progression tracking code
                        }
                       completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
                            if (image && finished) {
                                // do something with image
                                // Assign Image to ImageView and stop activity Indicator View
                            }
                        }];

SDWebImage链接：https://github.com/rs/SDWebImage

或者您可以使用自己的代码在GCD dispatch_async的帮助下下载图像，如下所述。

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^(void) {
                    //  You may want to cache this explicitly instead of reloading every time.
                    NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[self.loader.parsedData[indexPath.row] objectForKey:@"imageLR"]]];
                    UIImage* image = [[UIImage alloc] initWithData:imageData];
                    dispatch_async(dispatch_get_main_queue(), ^{
                        // Capture the indexPath variable, not the cell variable, and use that
                        UITableViewCell *blockCell = [tableView cellForRowAtIndexPath:indexPath];
                        blockCell.imageView.image = image;
                        [blockCell setNeedsLayout];
                        //Stop Your ActivityIndicator View hare 
                    });
                });

希望它会帮助您。

Answer 2

使用此方法在图像下载块代码之前开始动画。

[myActivityIndicator startAnimating];

并使用像这样的iOS块停止在图像下载中...

SDWebImageDownloader *downloader = [SDWebImageDownloader sharedDownloader];
[downloader downloadImageWithURL:imageURL
                     options:0
                    progress:^(NSInteger receivedSize, NSInteger expectedSize) {
                        // progression tracking code
                    }
                   completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
                        [myActivityIndicator startAnimating];
                        if (image && finished) {

                        }
                    }];