Swift Optionals错误

Question

我收到以下代码的错误。它来自data.writeToFile。我尝试过photoPath，photoPath！，photoPath？但它总是会出错。错误是：getData调用中的extraArgument（这不是错误，因为当我注释掉data.writeToFile时它工作正常）。

let file = object.objectForKey("image") as PFFile
let photoPath = NSURL.fileURLWithPath(NSTemporaryDirectory())?.URLByAppendingPathComponent("object", isDirectory: true).URLByAppendingPathExtension("jpg")

file.getDataInBackgroundWithBlock({ (data: NSData!, error: NSError!) -> Void in
    data.writeToFile(photoPath!, atomically: true)        
}, progressBlock: { (progress: Int32) -> Void in
    println(progress)
})

Answer 1

听起来像Swift试图捕获writeToFile（）的返回值并隐式地从闭包中返回它。你只需要明确在这里返回什么。

file.getDataInBackgroundWithBlock({ (data: NSData!, error: NSError!) -> Void in
    data.writeToFile(photoPath!, atomically: true)
    return        
}, progressBlock: { (progress: Int32) -> Void in
    println(progress)
})