您可以使用completion:函数，首先启动activityIndicator并停止指示器，当您在completion块中获得图像时，就像这样。

self.activityIndicator.startAnimating()
self.listImageView.af_setImageWithURL(
    NSURL(string: list!.image!)!,
    placeholderImage: nil,
    filter: nil,
    imageTransition: .CrossDissolve(0.5),
    completion: { response in
        let image = response.result.value // UIImage Object
        self.activityIndicator.stopAnimating()
    }
)

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我已经为UIImageView创建了扩展。查看link
上面的链接包含所有必需的方法，并根据您的要求进行必要的更改，以显示和隐藏活动指示器。

func downloadImage(withURL url: URL, placeholderImage: UIImage? = nil, completion: ((AFIDataResponse<UIImage>) -> Void)? = nil) {
    //Show activity indicator
    self.showActivityIndicator()
    self.af.setImage(withURL: url, placeholderImage: placeholderImage, completion: { response in
        if case .success(_) = response.result {
            //Hide activity indicator
            self.hideActivityIndicator()
        }
        
        completion?(response)
    })
}

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