Creating a UISwitch Programmatically

Question

In a seemingly never ending effort to learn more about iphone development, I have been playing around with some of the source code available through apples developer website

Answer 1

The compiler is trying to help you out. You're overriding the onoff instance variable in your viewDidLoad; thus, that's never getting set. In your -flip: method, you're referencing a nil controller. There are two ways to fix this:

(a) Get rid of the local declaration of onoff, and just use your instance variable

(b) Cast the sender argument to -flip: as a UISwitch, and access that:

- (IBAction) flip: (id) sender {
    UISwitch *onoff = (UISwitch *) sender;
    NSLog(@"%@", onoff.on ? @"On" : @"Off");
}

Answer 2

Steve, I'm sorry if I misunderstood your question. Did you actually create the UISwitch and add it to the view hierarchy? Your controller's -loadView or -viewDidLoad implementation should have code like the following:

// Use the ivar here
onoff = [[UISwitch alloc] initWithFrame: CGRectZero];
[onoff addTarget: self action: @selector(flip:) forControlEvents: UIControlEventValueChanged];
// Set the desired frame location of onoff here
[self.view addSubview: onoff];
[onoff release];