Gilberto Ibarra Gilberto Ibarra - 19 days ago 10
Swift Question

Set Action Listener Programmatically in Swift

I saw some example codes that assign the same OnClick event to all the buttons in Android (even if they perform completely different action) . How can do it with Swift

Android Example:

@Override
public void onCreate(Bundle savedInstanceState) {
button1.setOnClickListener(onClickListener);
button2.setOnClickListener(onClickListener);
button3.setOnClickListener(onClickListener);
}

private OnClickListener onClickListener = new OnClickListener() {
@Override
public void onClick(View v) {
switch(v.getId()){
case R.id.button1:
//DO something
break;
case R.id.button2:
//DO something
break;
case R.id.button3:
//DO something
break;
}

}
};


Note: I don't want create the button programatically.

Answer

On iOS, you're not setting a listener; you add a target (an object) and an action (method signature, "selector" in iOS parlance) to your UIControl (which UIButton is a subclass of):

button1.addTarget(self, action: "buttonClicked:", for: .touchUpInside)
button2.addTarget(self, action: "buttonClicked:", for: .touchUpInside)
button3.addTarget(self, action: "buttonClicked:", for: .touchUpInside)

The first parameter is the target object, in this case self. The action is a selector (method signature) and there are basically two options (more on that later). The control event is a bit specific to the UIControl - .TouchUpInside is commonly used for tapping a button.

Now, the action. That's a method (the name is your choice) of one of the following formats:

func buttonClicked()
func buttonClicked(_ sender: AnyObject?)

To use the first one use "buttonClicked", for the second one (which you want here) use "buttonClicked:" (with trailing colon). The sender will be the source of the event, in other words, your button.

func buttonClicked(_ sender: AnyObject?) {
  if sender === button1 {
    // do something
  } else if sender === button2 {
    // do something
  } else if sender === button3 {
    // do something
  }
}

(this assumes that button1, button2 and button3 are instance variables).

Instead of this one method with the big switch statement consider using separate methods for each button. Based on your specific use case either approach might be better:

func button1Clicked() {
  // do something
}

func button2Clicked() {
  // do something
}

func button3Clicked() {
  // do something
}

Here, I'm not even using the sender argument because I don't need it.

P.S.: Instead of adding targets and actions programmatically you can do so in your Storyboard or nib file. In order to expose the actions you put IBAction in front of your function, e.g.:

@IBAction func button1Clicked() {
  // do something
}