Swift中的回调函数语法 [英] Callback function syntax in Swift
问题描述
这是我的代码:
func showStandardPrompt(提示:String,view:UIViewController,numberInput:Bool,callback:(() - >(String))?){
let alert = UIAlertController(title:Input Data,message:prompt,preferredStyle:.Alert)
alert.addTextFieldWithConfigurationHandler {(textField)in
if numberInput {
textField.keyboardType = .NumberPad
}
}
在
中让OKAction = UIAlertAction(title:OK,style:.Default){(action)let field = alert .textFields![0] as UITextField
callback?(field.text!)
}
alert.addAction(OKAction)
let CancelAction = UIAlertAction(title: 取消,样式:.Default,处理程序:无)
alert.addAction(CancelAction)
view.presentViewController(alert,animated:true,完成:无)
}
我得到的错误是
callback?(field.text!)
错误是无法将'String'的值类型转换为期望的参数类型'()'。我知道这是一个语法问题 - 只是不知道它应该是什么。
Rob的回答是正确的,尽管我我想分享一个简单的工作回调/完成处理程序的例子,你可以在下面下载一个示例项目,并试验 getBoolValue
的输入。
下载示例项目
func getBoolValue(number:Int,completion:(result:Bool) - >()){
if号码> 5 {
completion(result:true)
} else {
completion(result:false)
}
}
getBoolValue(8 ){(结果) - > ()in
//做结果
print(result)
}
重要理解:
(String) - >()/ /需要一个字符串返回void
() - >(String)//获取void返回一个字符串
I am attempting pass a function to another function and then have the passed function executed passing to it a variable.
Here is my code:
func showStandardPrompt(prompt:String,view: UIViewController,numberInput: Bool, callback: (()->(String))?) {
let alert = UIAlertController(title: "Input Data", message: prompt, preferredStyle: .Alert)
alert.addTextFieldWithConfigurationHandler { (textField) in
if numberInput {
textField.keyboardType = .NumberPad
}
}
let OKAction = UIAlertAction(title: "OK", style: .Default) { (action) in
let field = alert.textFields![0] as UITextField
callback?(field.text!)
}
alert.addAction(OKAction)
let CancelAction = UIAlertAction(title: "Cancel", style: .Default, handler: nil)
alert.addAction(CancelAction)
view.presentViewController(alert,animated: true, completion: nil)
}
The error I get is in
callback?(field.text!)
The error is "Cannot convert value type of 'String' to expected argument type '()'. I know it's a matter of syntax - just don't know what it should be.
Rob's answer is correct, though I'd like to share an example of a simple working callback / completion handler, you can download an example project below and experiment with the getBoolValue
's input.
download example project
func getBoolValue(number : Int, completion: (result: Bool)->()) {
if number > 5 {
completion(result: true)
} else {
completion(result: false)
}
}
getBoolValue(8) { (result) -> () in
// do stuff with the result
print(result)
}
Important to understand:
(String)->() // takes a String returns void
()->(String) // takes void returns a String
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