Question

I am using storyboards and have dragged a scrollview window onto a view. In my code I am programmatically creating a switch object that is somehow not being initialized correctly. The switch appears on the view correctly but whenever I click the switch, an exception is thrown saying

“unrecognized selector sent to instance 0x6a786f0′”

I have also attempted to edit the On/Off text to Yes/No and accessing the switch also throws the same exception. Clearly I have missed something in creating my switch and setting the correct delegates or whatever.

My code to create the switch is..

        UISwitch *switchControl = [[UISwitch alloc] initWithFrame:CGRectMake(x, y, 60, 20)];
        [switchControl addTarget:inputsView action:@selector(actionSwitch:) forControlEvents:UIControlEventTouchUpInside];
        [switchControl setBackgroundColor:[UIColor clearColor]];
        //[(UILabel *)[[[[[[switchControl subviews] lastObject] subviews]
        //               objectAtIndex:1] subviews] objectAtIndex:0] setText:@"Yes"];
        //[(UILabel *)[[[[[[switchControl subviews] lastObject] subviews]
        //               objectAtIndex:1] subviews] objectAtIndex:1] setText:@"No"];


        [inputsView addSubview:switchControl];

inputsView is the name of my UIScrollView that I created in my .h file.

I should note, when the exception is called on clicking the switch, in the error the ‘reason’ is reason: ‘-[UIScrollView actionSwitch:]. When the error is called by trying to adjust the text, the ‘reason’ is reason: ‘-[UIImageView setText:]

Any help on what I am missing would be great.

Thanks

Answer 1

The exception is correct, UIScrolView does not have a method actionSwitch:. The target parameter in addTarget: is the object you want to receive the selector: argument.

If your posted code is in the class that has the actionSwitch: method then you would use self as the target, like so:

[switchControl addTarget:self action:@selector(actionSwitch:) forControlEvents:UIControlEventTouchUpInside];

And as a side note. For a UISwitch you generally want your method called for UIControlEventValueChanged, that way if the user just touches the switch but doesn’t “switch” it your method won’t be called.

Edit in response to: “I just tried changing to ‘self’ for the UISwitch and the error still occurs. I haven’t created an actionSwitch method.”

Yes, your application would still crash because whatever you pass in as the target must implement the selector/method passed in as the selector.

The view controller is the ideal place to implement this method. A very standard implementation of this event target would look like:

-(void)actionSwitch:(UISwitch *)theSwitch{
    if (theSwitch.isOn){
        // Switch was switched on respond accordingly 
    }
    else {
        // Switch was switched off respond accordingly 
    }
}