Activity 下载图片时的指示器 iOS

Question

我正在下载一组图像来创建动画。我怎样才能让下载开始时显示 activity 指示器以及下载完成时隐藏 activity 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，运行在后台线程上下载，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，这是当运行在后台时的样子：

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];

    });

});

Answer 2

下载开始时编写此代码： UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray] ; spinner.frame = CGRectMake(0, 0, 320, 50); [微调器启动动画];

下载结束时编写此代码：[spinner stopAnimating];

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