Question

How would I go about adding gesture events to uipickerview to change tabs? I have to create a custom class, however, I don’t know how to handle the uipickerview. I current have gestures present in uiviews to do this, but I’m having trouble with the uipickerview.

My code for the views:

#define HORIZ_SWIPE_DRAG_MIN 100
CGPoint mystartTouchPosition;
BOOL isProcessingListMove;
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint newTouchPosition = [touch locationInView:self.view];
    if(mystartTouchPosition.x != newTouchPosition.x || mystartTouchPosition.y != newTouchPosition.y) {
        isProcessingListMove = NO;
    }
    mystartTouchPosition = [touch locationInView:self.view];
    [super touchesBegan:touches withEvent:event];
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{
    UITouch *touch = touches.anyObject;
    CGPoint currentTouchPosition = [touch locationInView:self.view];

    // If the swipe tracks correctly.
    double diffx = mystartTouchPosition.x - currentTouchPosition.x + 0.1; // adding 0.1 to avoid division by zero
    double diffy = mystartTouchPosition.y - currentTouchPosition.y + 0.1; // adding 0.1 to avoid division by zero

    if(abs(diffx / diffy) > 2.5 && abs(diffx) > HORIZ_SWIPE_DRAG_MIN)
    {
        // It appears to be a swipe.
        if(isProcessingListMove) {
            // ignore move, we're currently processing the swipe
            return;
        }

        if (mystartTouchPosition.x < currentTouchPosition.x) {
            isProcessingListMove = YES;
            self.tabBarController.selectedViewController = [self.tabBarController.viewControllers objectAtIndex:0];
            return;
        }
        else {
            isProcessingListMove = YES;

            self.tabBarController.selectedViewController = [self.tabBarController.viewControllers objectAtIndex:2];

            return;
        }
    }
    else if(abs(diffy / diffx) > 1)
    {
        isProcessingListMove = YES;
        [super touchesMoved:touches withEvent:event];
    }
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{
    isProcessingListMove = NO;
    [super touchesEnded:touches withEvent:event];
}

Thanks for the help.

Answer 1

You can’t subclass UIPickerView.

However, since a picker view must be displayed in another view (since it doesn’t take up the entire screen) you can trap the touches in that view’s controller and filter for gestures.

(Assuming I understand what your trying to do…) I would warn that swiping a picker view to change tabs is a non-standard UI and will probably confuse your users. Since a picker view is perceived as a type of control, they will expect only the normal spinning action of the picker. How would they even know to swipe a picker view horizontally?