Question

我在Utilities类中使用了loadImage方法，并且在通过闭包返回图像方面遇到了一些麻烦。基本上是因为我的代码可以返回图像或错误，在调用方法时将其分配给图像属性将不起作用。

我在类的方法声明中使用了错误的方法，还是应该以不同的方式调用方法来预测可能不同的结果？感谢

public class UtilitiesService: NSObject {
    public class func loadImage(urlString:String)
    {

    var imgURL: NSURL = NSURL(string: urlString)!
    let request: NSURLRequest = NSURLRequest(URL: imgURL)
    NSURLConnection.sendAsynchronousRequest(
        request, queue: NSOperationQueue.mainQueue(),
        completionHandler: {(response: NSURLResponse!,data: NSData!,error: NSError!) -> Void in
            if error == nil {
                self.returnImage(data)
            }
    })
}

public class func returnImage(imageData: NSData) -> UIImage {

    return UIImage(data: imageData)!

}
}

//// view controller
class someView: UIViewController {
var image.image = loadImage(url) ///will throw a return type error
 }

Answer 1

为 loadImage func：

添加处理程序

Swift 3

 func loadImage(_ urlString: String, handler:@escaping (_ image:UIImage?)-> Void)
    {

        let imageURL: URL = URL(string: urlString)!

        URLSession.shared.dataTask(with: imageURL) { (data, _, _) in
            if let data = data{
                handler(UIImage(data: data))
            }
        }.resume()
    }

像这样调用func：

loadImage("SomeURL") { (image) -> Void in
            if let image = image{
                DispatchQueue.main.async {
                    self.imageView.image = image
                }
            }
        }

Swift 2.3

func loadImage(urlString: String, handler: (image:UIImage?)-> Void)
    {

        let imageURL: NSURL = NSURL(string: urlString)!

        NSURLSession.sharedSession().dataTaskWithURL(imageURL) { (data, _, _) in
            if let data = data{
                handler(image: UIImage(data: data))
            }
            }.resume()
    }

像这样调用func：

  loadImage("someURL") { (image) -> Void in
            if let image = image{
                dispatch_async(dispatch_get_main_queue()) {
                    self.imageView.image = image
                }
            }
        }

Answer 2

我会这样做：

public class UtilitiesService: NSObject {
    public class func loadImage(urlString:String, completion:(resultImage:UIImage) -> Void)
    {

    var imgURL: NSURL = NSURL(string: urlString)!
    let request: NSURLRequest = NSURLRequest(URL: imgURL)
    NSURLConnection.sendAsynchronousRequest(
        request, queue: NSOperationQueue.mainQueue(),
        completionHandler: {(response: NSURLResponse!,data: NSData!,error: NSError!) -> Void in
            if error == nil {
                completion(resultImage: UIImage(data: data))
            }
    })
}
}

//// view controller
class someView: UIViewController {
var image: UIImageView()? //Create the variable the way you need
loadImage(url, completion: { (resultImage) -> Void in
    image = resultImage //Assign the result to the variable
})
 }

我认为这样可行，如果没有，请告诉我，我会解决它

从完成处理程序返回值 - Swift

2 个答案: