xcode 9.0.1/swift 4，没有使用 Objective-C 选择器“onClick:forEvent:"声明的方法 [英] xcode 9.0.1 / swift 4, No method declared with Objective-C selector 'onClick:forEvent:'

问题描述

我使用 swift 4 来构建我的 UI，我创建了一个 UIButton 并想向它添加一个目标.

I use swift 4 to build my UI，I create a UIButton and want to add a target to it.

但是编译器抛出一个警告:No method created with Objective-C selector 'onClick:forEvent:'

But the complier throw an warning: No method declared with Objective-C selector 'onClick:forEvent:'

button.addTarget(self, action: Selector("onClick:forEvent:"), for: UIControlEvents.touchUpInside) 
//...

func onClick(_ sender: Any, forEvent event: UIEvent) {
  print("button click", sender, event);
}

当我单击警告三角形时尝试修复此问题.将选择器名称括在括号中以抑制此警告.

When I click the warning triangle try to fix this. Wrap the selector name in parentheses to suppress this warning.

它只是将选择器名称括在括号中.

It just wrap the selector name in parentheses.

button.addTarget(self, action: Selector(("onClick:forEvent:")), for: UIControlEvents.touchUpInside)

构建成功，但是当我单击按钮时.

build success, but when I click the button.

抛出错误

libc++abi.dylib:以 NSException 类型的未捕获异常终止

我知道可以改成#selector(ViewClass.methodName)和@objc func methodName() {..}方式.

I know it can be changed to #selector(ViewClass.methodName) and @objc func methodName() {..} way.

但是为什么 Selector 不起作用?这是正确的 swift 4 方式吗?

but why Selector not working ? Is this a correct swift 4 way?

推荐答案

您应该在函数前面加上 @objc 以使其对 Objective-C 运行时可见，例如:

You should prefix the function with @objc to make it visible to the Objective-C runtime, e.g.:

@objc func onClick(_ sender: Any, forEvent event: UIEvent)

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