Swift 3

let button = UIButton()
button.frame = CGRect(x: self.view.frame.size.width - 60, y: 60, width: 50, height: 50)
button.backgroundColor = UIColor.red
button.setTitle("your Button Name", for: .normal)
button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
self.view.addSubview(button)

func buttonAction(sender: UIButton!) {
    print("Button tapped")
}

Swift 4+

 let button = UIButton()
 button.frame = CGRect(x: self.view.frame.size.width - 60, y: 60, width: 50, height: 50)
 button.backgroundColor = UIColor.red
 button.setTitle("Name your Button ", for: .normal)
 button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
 self.view.addSubview(button)

 @objc func buttonAction(sender: UIButton!) {
    print("Button tapped")
 }

    // UILabel:
    let label = UILabel()
    label.frame = CGRectMake(35, 100, 250, 30)
    label.textColor = UIColor.blackColor()
    label.textAlignment = NSTextAlignment.Center
    label.text = "Hello World"
    self.view.addSubview(label)

    // UIButton:
    let btn: UIButton = UIButton(type: UIButtonType.Custom) as UIButton
    btn.frame = CGRectMake(130, 70, 60, 20)
    btn.setTitle("Click", forState: UIControlState.Normal)
    btn.setTitleColor(UIColor.blackColor(), forState: .Normal)
    btn.addTarget(self, action:Selector("clickAction"), forControlEvents: UIControlEvents.TouchUpInside)
    view.addSubview(btn)


    // Button Action:
    @IBAction func clickAction(sender:AnyObject)
    {
        print("Click Action")
    }

 var sampleButton:UIButton?

 override func viewDidLoad() {
  super.viewDidLoad()

 }
 override func viewDidAppear(animated: Bool) {

  sampleButton = UIButton(type: .RoundedRect)
  //sampleButton.frame = CGRect(x:50, y:500, width:70, height:50)

  sampleButton!.setTitle("Sample \n UI Button", forState: .Normal)
  sampleButton!.titleLabel?.lineBreakMode = .ByWordWrapping
  sampleButton!.titleLabel?.textAlignment = .Center
  sampleButton!.setTitleColor(UIColor.whiteColor(), forState: .Normal)
  sampleButton!.layer.cornerRadius = 6
  sampleButton!.backgroundColor = UIColor.redColor().colorWithAlphaComponent(0.6)
  sampleButton?.tintColor =  UIColor.brownColor()


  //Add padding around text
  sampleButton!.titleEdgeInsets = UIEdgeInsetsMake(-10,-10,-10,-10)
  sampleButton!.contentEdgeInsets = UIEdgeInsetsMake(5,5,5,5)

  //Action set up
  sampleButton!.addTarget(self, action: "sampleButtonClicked", forControlEvents: .TouchUpInside)
  self.view.addSubview(sampleButton!)


  //Button Constraints:
  sampleButton!.translatesAutoresizingMaskIntoConstraints = false

  //To anchor above the tab bar on the bottom of the screen:
  let bottomButtonConstraint = sampleButton!.bottomAnchor.constraintEqualToAnchor(bottomLayoutGuide.topAnchor, constant: -20)

  //edge of the screen in InterfaceBuilder:
  let margins = view.layoutMarginsGuide
  let leadingButtonConstraint = sampleButton!.leadingAnchor.constraintEqualToAnchor(margins.leadingAnchor)

  bottomButtonConstraint.active = true
  leadingButtonConstraint.active = true


 }
 func sampleButtonClicked(){

  print("sample Button Clicked")

 }

在Swift 4.2中编写下面的示例代码，用于以编程方式添加按钮。

override func viewDidLoad() {
    super.viewDidLoad()
        let myButton = UIButton(frame: CGRect(x: 100, y: 100, width: 100, height: 50))
        myButton.backgroundColor = .green
        myButton.setTitle("Hello UIButton", for: .normal)
        myButton.addTarget(self, action: #selector(myButtonAction), for: .touchUpInside)
        self.view.addSubview(myButton)
}

 @objc func myButtonAction(sender: UIButton!) {
    print("My Button tapped")
}

将此代码添加到viewDidLoad中 / /添加按钮

            var button=UIButton(frame: CGRectMake(150, 240, 75, 30))
            button.setTitle("Next", forState: UIControlState.Normal)
            button.addTarget(self, action: "buttonTapAction:", forControlEvents: UIControlEvents.TouchUpInside)
            button.backgroundColor = UIColor.greenColor()
            self.view.addSubview(button)

将这个函数写在它的外面，当你点击按钮时，这个函数将被调用

func buttonTapAction(sender:UIButton!)
{
    println("Button is working")
}

你可以这样创建，也可以这样添加动作....

import UIKit

let myButton = UIButton(frame: CGRect(x: 0, y: 0, width: 50, height: 50))

init(nibName nibNameOrNil: String!, bundle nibBundleOrNil: NSBundle!)
{       super.init(nibName: nibName, bundle: nibBundle) 
        myButton.targetForAction("tappedButton:", withSender: self)
}

func tappedButton(sender: UIButton!)
{ 
     println("tapped button")
}