ios - 下载图像 iOS 时的事件指示器

Question

我正在下载一组图像来创建动画。我怎样才能使下载开始时显示事件指示器以及下载完成时隐藏事件指示器。

self.img = [[UIImageView alloc] initWithFrame:CGRectMake(0, 65, self.view.frame.size.width, self.view.frame.size.width-70)];



        img.animationImages = [NSArray arrayWithObjects:

                                   [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],

                                   [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],

                                   [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],

                                   [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],




        img.animationDuration = 20.0f;

        img.animationRepeatCount = 0;

        [img startAnimating];

        [self.view addSubview: img];

Answer 1

您的图片正在同步下载，这意味着您正在阻塞主线程(这很糟糕)。相反，在后台线程上运行下载，这将允许主线程，并且在扩展中，您的应用程序的 UI 仍然可以运行。使用您的示例代码，这是在后台运行时的样子:

self.img = [[UIImageView alloc] initWithFrame:CGRectMake(0, 65, self.view.frame.size.width, self.view.frame.size.width-70)];
self.img.animationDuration = 20.0f;
self.img.animationRepeatCount = 0;
[self.img startAnimating];
[self.view addSubview:self.img];

// START ANIMATING YOUR ACTIVITY INDICATOR HERE

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {

    NSArray *images = @[
        [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],
        [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],
        [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],
        [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"URL"]]],
    ];

    dispatch_async(dispatch_get_main_queue(), ^(void) {

        // STOP ANIMATING YOUR ACTIVITY INDICATOR HERE

        [self.img setAnimationImages:images];

    });

});