我正在 F# 中实现以下 Swift 方法:
func downloadCachedImage(url : URL) {
if let cachedImage = imageCache.object(forKey: url.absoluteString as AnyObject) {
self.image = cachedImage as! UIImage
}
URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
if (error != nil) {
print(error)
return
}
DispatchQueue.main.async {
if let downloadedim = UIImage(data: data!) {
imageCache.setObject(downloadedim, forKey: url.absoluteString as AnyObject)
self.image = downloadedim
}
}
}).resume()
}
我通过以下方式实现了它:
member this.downloadCachedImage(url : NSUrl) =
if imageCache.ObjectForKey(NSObject.FromObject(url.AbsoluteString)) <> null then
this.Image <- imageCache.ObjectForKey(NSObject.FromObject(url.AbsoluteString)) :?> UIImage
else
let session : NSUrlSession = NSUrlSession.SharedSession
let request : NSUrlRequest = NSUrlRequest.FromUrl(url)
let downloadTask : NSUrlSessionDataTask = session.CreateDataTask(request, fun data response error ->
if error <> null then
printfn "Error occurred"
else
let image = UIImage.LoadFromData(data)
imageCache.SetObjectforKey(image,new NSString(url.AbsoluteString))
this.Image <- image
)
downloadTask.Resume()
我唯一的问题是我需要代码:
this.Image <- image
在更新 UI 时在主线程上运行。在 Swift 中,这是通过以下块实现的:
DispatchQueue.main.async {...}
但是,我不知道如何在 F# 中执行此操作。
您可以尝试返回主线程:
InvokeOnMainThread(fun _ -> ... )
但我认为当你从completionHandler
,它已经在主线程上了。
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