在Swift 4 Xcode 9 Beta 6中无法对UIButton进行编程，无法添加目标 [英] Programming a UIButton is not working in Swift 4 Xcode 9 Beta 6, Cannot add target

问题描述

过去，我可以通过编程方式创建UIButton没问题，但是自从我一直在使用Xcode 9和Swift 4以来，我一直找不到解决这个错误的方法.

In the past I had no problem creating a UIButton programmatically, but ever since I've been using Xcode 9 and Swift 4, I cannot find a way to make this error go away.

//Adding target to UIButton
func PositionStartButton(xOffset: Float){
    StartButton.frame = CGRect(x: Int(0 - 40 + xOffset), y: 0, width: 80, height: 80)
    StartButton.setImage(#imageLiteral(resourceName: "Logo_Final_WHITE_Face"), for: .normal)
    StartButton.addTarget(self, action: "pressButton:", for: .touchUpInside)
    ScrollView.addSubview(StartButton)

}

//The target function
func pressButton(_ sender: UIButton){
    print("\(sender)")
}

错误消息:"NSInvalidArgumentException"，原因:-[Playing.MainMenuViewController pressButton:]:无法识别的选择器已发送到实例0x10440a6b0"

Error Message: 'NSInvalidArgumentException', reason: '-[Playing.MainMenuViewController pressButton:]: unrecognized selector sent to instance 0x10440a6b0'

推荐答案

两点.

首先，由于Swift 2.2(与一年多以前发布的Xcode 7.3捆绑在一起)，推荐的选择器表示法为#selector(...).与使用其他表示法相比，使用该表示法可能会获得更多有用的诊断消息.

First, since Swift 2.2 (bundled with Xcode 7.3, released more than a year ago), recommended selector notation is #selector(...). With using the notation, you may get more useful diagnostic messages, than using other notation.

(您不应忽略使用建议设置显示的任何警告.)

(You should not ignore any warnings displayed with recommended settings.)

第二，在Swift 4中，您需要使用@objc显式注释通过选择器调用的方法. (在极少数情况下，Swift会隐式地应用该表示法，但数量并不多.)

Seconde, in Swift 4, you need to explicitly annotate methods invoked through selector with @objc. (In very limited cases, Swift implicitly applies the notation, but not many.)

因此，您显示的代码应为:

So, your code shown should be:

//Adding target to UIButton
func PositionStartButton(xOffset: Float){
    StartButton.frame = CGRect(x: Int(0 - 40 + xOffset), y: 0, width: 80, height: 80)
    StartButton.setImage(#imageLiteral(resourceName: "Logo_Final_WHITE_Face"), for: .normal)
    StartButton.addTarget(self, action: #selector(self.pressButton(_:)), for: .touchUpInside) //<- use `#selector(...)`
    ScrollView.addSubview(StartButton)

}

//The target function
@objc func pressButton(_ sender: UIButton){ //<- needs `@objc`
    print("\(sender)")
}

---

这并不重要，但是您最好遵循Swift的简单编码规则-仅将类型名大写.

---

This is not critical, but you should better follow a simple coding rule of Swift -- only type names are capitalized.

如果您认为您可能还有另一次公开展示代码的机会，最好重命名您的PositionStartButton，StartButton和ScrollView.

Better rename your PositionStartButton, StartButton and ScrollView, if you think you may have another chance to show your code publicly.

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