Question

When coding with cocoa I’ve noticed that it’s not necessary to have sender parameter when defining IBAction, hence following action:

- (IBAction)showUserInfo:(id)sender;

can be declared as

- (IBAction)showUserInfo;

So I’m wondering if there is any other benefit besides having the button/menu item that sent the action? Only other situation I can think of is having few objects calling same IBAction. Anything else?

Answer 1

It can be handy to use the sender argument when you’re connecting the method to UI objects whose values can change and you may need to work with.

For instance if I wired up a method to a UISegmentedControl and set it’s control event to UIControlEventValueChanged, I can use the object passed as the sender: argument to obtain it’s selected segment index and then, based on the value, make a change in the UI.

-(IBAction)segmentedControlValueChanged:(id)sender
{
    UISegmentedControl *control = (UISegmentedControl *)sender;

    // Show or hide views depending on the selected index of the segmented control.
    if (control.selectedSegmentIndex == 0)
        someView.hidden = YES;
    else 
        someView.hidden = NO;
}