在Swift中以编程方式创建UIButton

Question

我正在尝试以编程方式构建UI。如何使该动作起作用？我正在用Swift开发。

viewDidLoad中的代码：

override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let myFirstLabel = UILabel()
        let myFirstButton = UIButton()
        myFirstLabel.text = "I made a label on the screen #toogood4you"
        myFirstLabel.font = UIFont(name: "MarkerFelt-Thin", size: 45)
        myFirstLabel.textColor = UIColor.redColor()
        myFirstLabel.textAlignment = .Center
        myFirstLabel.numberOfLines = 5
        myFirstLabel.frame = CGRectMake(15, 54, 300, 500)
        myFirstButton.setTitle("✸", forState: .Normal)
        myFirstButton.setTitleColor(UIColor.blueColor(), forState: .Normal)
        myFirstButton.frame = CGRectMake(15, -50, 300, 500)
        myFirstButton.addTarget(self, action: "pressed", forControlEvents: .TouchUpInside)
        self.view.addSubview(myFirstLabel)
        self.view.addSubview(myFirstButton)
    }

        func pressed(sender: UIButton!) {
            var alertView = UIAlertView();
            alertView.addButtonWithTitle("Ok");
            alertView.title = "title";
            alertView.message = "message";
            alertView.show();
        }

Answer 1

您只是在选择器名称的末尾缺少冒号。因为按下需要一个参数，所以冒号必须在该位置。而且，您按下的函数不应嵌套在viewDidLoad中。

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    let myFirstLabel = UILabel()
    let myFirstButton = UIButton()
    myFirstLabel.text = "I made a label on the screen #toogood4you"
    myFirstLabel.font = UIFont(name: "MarkerFelt-Thin", size: 45)
    myFirstLabel.textColor = UIColor.redColor()
    myFirstLabel.textAlignment = .Center
    myFirstLabel.numberOfLines = 5
    myFirstLabel.frame = CGRectMake(15, 54, 300, 500)
    myFirstButton.setTitle("✸", forState: .Normal)
    myFirstButton.setTitleColor(UIColor.blueColor(), forState: .Normal)
    myFirstButton.frame = CGRectMake(15, -50, 300, 500)
    myFirstButton.addTarget(self, action: #selector(myClass.pressed(_:)), forControlEvents: .TouchUpInside)
    self.view.addSubview(myFirstLabel)
    self.view.addSubview(myFirstButton)
}

@objc func pressed(sender: UIButton!) {
    var alertView = UIAlertView()
    alertView.addButtonWithTitle("Ok")
    alertView.title = "title"
    alertView.message = "message"
    alertView.show()
}

编辑：更新以反映Swift 2.2中的最佳实践。应该使用#selector（）而不是不推荐使用的文字字符串。