如何在 Swift 中创建一个带有完成处理程序的函数? [英] How could I create a function with a completion handler in Swift?
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问题描述
我只是想知道我将如何处理这个问题.如果我有一个函数,我想在它完全执行时发生一些事情,我该如何将它添加到函数中?谢谢
I was just curious as to how I would approach this. If I had a function, and I wanted something to happen when it was fully executed, how would I add this into the function? Thanks
推荐答案
假设您有一个从网络下载文件的下载功能,并希望在下载任务完成时收到通知.
Say you have a download function to download a file from network, and want to be notified when download task has finished.
typealias CompletionHandler = (success:Bool) -> Void
func downloadFileFromURL(url: NSURL,completionHandler: CompletionHandler) {
// download code.
let flag = true // true if download succeed,false otherwise
completionHandler(success: flag)
}
// How to use it.
downloadFileFromURL(NSURL(string: "url_str")!, { (success) -> Void in
// When download completes,control flow goes here.
if success {
// download success
} else {
// download fail
}
})
希望有帮助.
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