Question

I have a UIPicker and have setup my delegate methods.

I want something to happen when the user TAPS on the selected picker item. Handling it in:

- (void)pickerView:(UIPickerView *)aPickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component

Triggers the event to occur when the picker item is selected not tapped.

How can I trigger an event when the selected picker item is tapped?

Answer 1

You have to sub class UIPickerView and detect the touches there manually. Yes, it looks messy. But that seems to be the only way to do this. The below code may help,

@interface TouchDetectionView : UIPickerView {

}
- (UIView *)getNextResponderView:(NSSet *)touches withEvent:(UIEvent *)event;
@end
@implementation TouchDetectionView

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
    [hitTestView touchesBegan:touches withEvent:event];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
    [hitTestView touchesMoved:touches withEvent:event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
    [hitTestView touchesEnded:touches withEvent:event];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    UIView * hitTestView = [self getNextResponderView:touches withEvent:event];
    [hitTestView touchesCancelled:touches withEvent:event];
}

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
    return self;
}

- (UIView *)getNextResponderView:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch * touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    UIView * hitTestView = [super hitTest:point withEvent:event];

    return ( hitTestView == self ) ? nil : hitTestView;
}

Ref: Responding to touchesBegan in UIPickerView instead of UIView