Interface analog in Swift for callbacks realization - swift

Question

Please, help me to make interface in Swift to use it for callbacks purposes.
Example in Java:
public interface ErrorListener {
void onError(String errorMsg);
}
class SomeUiClass implements ErrorListener {
public SomeUiClass () {
SomeWorkingClass s = new SomeWorkingClass();
s.setErrorListener(this);
s.doSomething(true);
}
#Override
void onError(String errorMsg) {
System.out.println("Error msg: " + errorMsg);
}
}
class SomeWorkingClass {
ErrorListener listener;
void setErrorListener (ErrorListener listener) {
this.listener = listener;
}
void doSomething (boolean withError) {
if (withError) listener.onError("Test error");
}
}
//....
SomeUiClass ui = new SomeUiClass(); // prints: Error msg: Test error
So, I tried to use protocol in Swift for this purpose, but I didn't understand, how to use it properly.

Answer 1

It would look like this in swift
protocol ErrorListener {
func onError(errorMsg:String)
}
class SomeUiClass : UIViewController , ErrorListener {
func onError(errorMsg:String)
print("Error msg: ", errorMsg)
}
}
class SomeWorkingClass : UIViewController{
weak var listener:ErrorListener?
func setErrorListener (listener:ErrorListener) {
self.listener = listener
}
}
let ui = SomeUiClass() // prints: Error msg: Test error