How to handle UITapGestureRecognizer in a subview?

Question

I have a viewcontroller (vc1) in which I added another viewcontroller (vc2) as a subview. An UITapGestureRecognizer is triggered when you tap on a view (tappingView) contained in the subview (vc2). I would like to handle this tap inside the subview controller (vc2), and not from the first viewcontroller (vc1)... but it keeps crashing when I click on my view.

Here is the hierarchy sum up :

-vc1
--vc2
---tappingView

And here is a sample of code :

ViewController1 (viewDidLoad):

- (void)viewDidLoad
{
    ViewController2 *vc2 = [[ViewController2 alloc] init];
    [[self view] addSubview:[vc2 view]];
}

ViewController2 (viewDidLoad):

- (void)viewDidLoad
{
    UIView *tappingView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 60.0, 80.0)];
    [[self view] addSubview:tappingView];
    UITapGestureRecognizer *tapGestureRecognize = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(singleTapGestureRecognizer:)];
    [tappingView addGestureRecognizer:tapGestureRecognize];
}

ViewController2 (singleTapeGestureRecognizer:) :

- (void)singleTapGestureRecognizer:(id)sender {
    NSLog(@"Tap gesture");
}

When I click in my view (tappingView), I keep getting a crash (BAD_ACCESS).

Anyone have an idea why ?

Answer 1

You shouldn't just add another view controller's view to your view -- you should make that controller a childViewController of vc1. Change the viewDidLoad in vc1 to this:

- (void)viewDidLoad {

    ViewController2 *vc2 = [[ViewController2 alloc] init];
    [self addChildViewController:vc2];
    [vc2 didMoveToParentViewController:self];
    [[self view] addSubview:[vc2 view]];
}

It's not clear why you're doing it this way in the first place. Why not present vc2 as a modal view controller instead?

Answer 2

In this block

- (void)viewDidLoad
{
    ViewController2 *vc2 = [[ViewController2 alloc] init];
    [[self view] addSubview:[vc2 view]];
}

your ViewController2 is not retained (addSubview only retains the view, not the view controller).

To fix it, declare vc2 as a strong property, instead of a variable.

self.vc2 = [[ViewController2 alloc] init];

Or better, as someone suggested, add vc2 as a child view controller.

Answer 3

Targets of UITapGestureRecognizer take the UIGestureRecognizer argument, not id. I.e.:

- (void)singleTapGestureRecognizer:(UIGestureRecognizer *)sender {
  NSLog(@"Tap gesture");
}

Further, you're setting frames in viewDidLoad, which you should do in viewWillAppear: instead.

Answer 4

use below code

- (void)singleTapGestureRecognizer:(UIGestureRecognizer *)sender 

instead of

- (void)singleTapGestureRecognizer:(id)sender.

As it must have UIGestureREcognizer instead of id.`