Question

I’m just learning how to use the C4 framework and trying to add gestures to a shape, but I can’t seem to figure out how to get them to do anything. The following method creates an error, when I try to change the position of a button after it is tapped.

[buttonA addGesture:TAP name:@"tapGesture" action:@"setPosition"];

This is the error I get: * Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[MyButton setPosition]: unrecognized selector sent to instance 0x7661b60’

Answer 1

I’m guessing that the reason you’re getting the error is because the setPosition method is because you’re trying to run the setPosition method directly on a C4Shape object. Natively, C4Shapes don’t have this method.

In C4, all objects can have gestures attached to them, but in order run any custom code when you trigger a gesture on an object you should first subclass C4Shape and write a special method to handle the behaviour you want to see.

For example, I would create a MyShape class like this:

@interface MyShape : C4Shape
-(void)setNewPosition;
@end

@implementation MyShape
-(void)setNewPosition {
    //will set the center of the shape to a new random point
    self.center = CGPointMake([C4Math randomInt:768], [C4Math randomInt:1024]);
}
@end

Then, in my C4WorkSpace:

#import "C4WorkSpace.h"
#import "MyShape.h"

@implementation C4WorkSpace {
    MyShape *newShape;
}
-(void)setup {
    newShape = [MyShape new];
    [newShape ellipse:CGRectMake(100, 100, 200, 200)];
    [newShape addGesture:TAP name:@"tapGesture" action:@"setNewPosition"];
    [self.canvas addShape:newShape];
}
@end

This should register a tap gesture with your new subclassed shape, and run its setNewPosition method when the gesture is triggered.