Swift 3 and unrecognized selector sent to instance error for button creation [duplicate]

Question

After we start using Swift 3 we have been faced with this 'unrecognized selector sent to instance! error and could not find the solution at reasonable time. All the answers we have encountered for older version of Swift. This is the declaration of action we came up with

     testbutton.addTarget(self, action: Selector("testButtonAction:"), for: UIControlEvents.touchDown)

and this is the "corrected" version by Xcode but neither of them is working.

     testbutton.addTarget(self, action: Selector(("testButtonAction:")), for: UIControlEvents.touchDown)

This is the action function.

       func testButtonAction(sender: UIButton!) {

            print("Button tapped")

          }

Answer 1

The correct syntax for Swift 3 is:

testbutton.addTarget(self, action: #selector(testButtonAction(sender:)), for: UIControlEvents.touchDown)

Any mistakes here will now be picked up at compile time rather than run time.

Answer 2

It should be like this:

testButton.addTarget(self, action: #selector(YourViewController.testButtonAction(sender:)), for: UIControlEvents.touchDown)