Question

It seems like this should be simple, but it is apparently not so.

I am using Storyboards, with my first view controller defined as LogbookFirstViewController.

The contents of this controller are inside of a UIControl. That way I can detect taps.

However, I can see no easy way to determine when a user has started swiping across the screen. All I want to do is get the touches x-coordinate. Essentially track it.

I dropped a UIPanGestureRecognizer inside LogbookFirstViewController, and attached it’s outlet too:

In .h

@property (assign) IBOutlet UIGestureRecognizer *gestureRecognizer;

Of course, I then synthesized it and set the delegate:

In .m

[gestureRecognizer setDelegate:self];

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{

    UITouch *touchLoc = [touches anyObject];
    CGPoint beginCenter = self.view.center;
    CGPoint touchPoint = [touchLoc locationInView:self.view];

    deltaX = touchPoint.x - beginCenter.x;
    deltaY = touchPoint.y - beginCenter.y;
    NSLog(@"X = %f & Y = %f", deltaX, deltaY);
}

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

    // Set the correct center when touched
    touchPoint.x -= deltaX;
    touchPoint.y -= deltaY;

    self.view.center = touchPoint;
}

However, this does nothing. It doesn’t even detect -(void)touchesBegan

What am I missing? Thanks in advanced.

Answer 1

Those methods are not delegate methods, they’re only for subclassing UIGestureRecognizer.

Typically you instantiate a gesture recognizer and specify a selector (a method) to call when that gesture is recognized and then you assign it to a view, for example:

UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
[self.view addGestureRecognizer:pan]

Then in your pan method you can query information from teh gesture:

- (void)pan:(UIPanGestureRecognizer *)gesture
{
    // get information from the gesture object
}

I’ve never done it with a StoryBoard but I suppose if you have a property already in your view controller you could call addTarget:action: and attach it to a view in the view controllers viewDidLoad method.