iPhone SDK: Interact with Images

I was making an app for the iPhone and part of开发者_运维问答 what I want to do is that whenever the user touches a certain spot (let's say a circle), the app should react and do something.

How do I pinpoint that one spot as a button? Or is there a different way to do this? I have a UIScrollView with a subview of a UIImageView.

Thanks in advance!

Guy

You can learn how to handle touch from the Touches sample.

In particular, handling a simple touch happens in instances of the UIResponder class. Since UIView inherits from UIResponder, any view is capable of responding to the touch messages. Thus, in order to handle touch, you just need to create a class that inherits from the particular view (UIScrollView in your case) and overwrite the touch invent you are interested; more specifically, for your scenario you need to handle the touchesEnded:withEvent:.

Easiest way to do this is add some transparent UIButton instances on UIScrollView, set actions and do something in each button.

for example,

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

// Override point for customization after application launch

...

UIButton* someButton = [[[UIButton alloc] initWithFrame:CGRectMake(100.0f, 100.0f, 100.0f, 100.0f)] autorelease];
[someButton addTarget:self action:@selector(doSomething) forControlEvents:UIControlEventTouchDown];
[someUIScrollView addSubview:someButton];

...
}

- (void)doSomething {
    NSLog(@"Do something");
}

You should write some codes for judging whether touched point is inside or not, if you want to create non-rect spot (such as circle). But considering finger size and user recognition, I think you don't have to implement a strict judgement.