I have a UIImageView inside of a custom cell. I am creating a custom tap gesture recognizer for when the UIImageView is tapped to load another detail view.
The tap gesture is set up like so:
UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(imageTapped:event:)];
tapRecognizer.cancelsTouchesInView = YES;
tapRecognizer.numberOfTapsRequired = 1;
tapRecognizer.delegate = (id)self;
[cell.userImage addGestureRecognizer:tapRecognizer];
cell.userImage.userInteractionEnabled = YES;
I am using imageTapped:event: so that I can detect what cell the user is tapping and load the data accordingly. The problem is I get this error:
If I get rid of event like so, its works perfectly with no issues.
UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(imageTapped:)];
I have used this method before in another application but for some reason I cannot get it to work properly with this error. Anyone recognize what this is? Thanks!
You need to read the documentation on UIGestureRecognizer...
A gesture recognizer has one or more target-action pairs associated
with it. If there are multiple target-action pairs, they are discrete,
and not cumulative. Recognition of a gesture results in the dispatch
of an action message to a target for each of those pairs. The action
methods invoked must conform to one of the following signatures:
- (void)handleGesture;
- (void)handleGesture:(UIGestureRecognizer *)gestureRecognizer;
Using one of these signatures will prevent the crash as you have already observed. You could then access the image view that was involved in the gesture by inspecting the recognizer's view property, and from this you will be able to access the appropriate UITableView cell.
Related
I have set two UITapGestureRecognizers in my xib on a UIImageView. I have also set their IBAction in the associated header file.
For the single tap gesture recognizer, I set taps and touches to 1, state to Enabled, and delayed touches ended to YES in the Attributes inspector.
For the double tap gesture recognizer, I set taps and touches to 2, state to Enabled, cancel touches in view to YES and delay touches ended to YES.
When I double tap on the UIImageView, it only triggers the IBAction method for the single tap. So, I decided to print the imageview.gestureRecognizer and it shows the UITapGestureRecognizer for single tap's state as Ended and the UITapGestureRecognizer for double tap's state as Possible.
I have been stuck on this for a couple hours. I found ways to do it programatically but I was wondering how I can do it by setting it in the xib itself.
Any help would be great! Thank you in advance for your responses!
It's a very good question. If you add gestures to code like this
UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget: self action:#selector(singleTap)];
singleTap.numberOfTapsRequired = 1;
[self.view addGestureRecognizer:singleTap];
UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget: self action:#selector(doubleTap)] ;
doubleTap.numberOfTapsRequired = 2;
[self.view addGestureRecognizer:doubleTap];
[singleTap requireGestureRecognizerToFail:doubleTap];
And all works fine because you canceled first gesture here
[singleTap requireGestureRecognizerToFail:doubleTap];
If you add two gestures in xib you always should cancel single tap if there was a double tap. And you always need to use 2 properties for gestures and use
[self.firstGestureProperty requireGestureRecognizerToFail:self.secondGestureOroperty];
For single tap:
For double tap:
Source code:
And everything works fine.
I was looking for GestureRecognizer tutorials on the web and saw that most people used for example UIPanGestureRecognizer directly in the view. Is this common practice, if so, why not in the controller?
I generate my views in the controller and have methods that I would need to call, when the gesture is used. How should the delegation method look like, if my gesture recognizer is in the view class, and the method to be called in the controller class?
A simple UIGestureRecognizer implementation, and the most common one in my opinion is as follows:
//this is where you create the view that you want to add the gesture recognizer
UIImageView * imageView = [[UIImageView alloc] initWithFrame:frame];
UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] init];
tapRecognizer.numberOfTapsRequired = 1;
[tapRecognizer addTarget:self action:#selector(imageViewTapped:)];
imageView.userInteractionEnabled = YES;
[imageView addGestureRecognizer:tapRecognizer];
After creating the gesture recognizer and adding it to a UIView subclass you can get the taps with the function you pointed above:
- (void)imageViewTapped:(UIGestureRecognizer *)gestureRecognizer
{
if ( gestureRecognizer.state == UIGestureRecognizerStateRecognized )
{
NSLog(#"tap recognized!");
}
}
So basically, you dont need to worry about the controller/view dilemma.
You always add the gesturerecognizer to a view. and when adding the gesture recognizer you add a target function, which you need to implement in the controller class.
P.S This SO Question might clarify in detail of the dilemma you are facing
In one sense, yes, this violate the MVC pattern. As you say, the view shouldn't have anything to do with how to control it, it's a better habit to group such code in another part of the application.
You can drag an gesture into the storyboard(into the view controller),too.Then from the document outline you make an action(in the vc) for that gesture
I have a longpress gesture recognizer that I create in ViewDidLoad then attach to a button like this, the button is created in the storyboard and linked to my class.
UILongPressGestureRecognizer *hold = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:#selector(secretChange:)];
hold.minimumPressDuration = 5.0;
hold.delegate = self;
[_button addGestureRecognizer:hold];
The class conforms to the GestureRecognizer protocol and I have my selector here
- (void)secretChange:(UILongPressGestureRecognizer *)sender {
// Some stuff
NSLog(#"Secret");
}
The selector is not being called and I cannot figure out why, this seems to be the code everyone gives out on the internet, I have tried removing the minimum duration to make sure I didn't accidentally set it ridiculously long
UPDATE: I am actually adding this gesture recognizer to multiple buttons like this
[_button1 addGestureRecognizer:hold];
[_button2 addGestureRecognizer:hold];
[_button3 addGestureRecognizer:hold];
What is happening is the gesture recognizer is only being applied to the last button I add it to. How do I get the gesture recognizer added to ALL the buttons? Do I need to make a new one for every button?
You should have three instance of UILongPressGestureRecognizer.
Before add a gesture recognizer to a new view, the addGestureRecognizer method will remove the gesture recognizer from the view it has been attached to.
I'm somewhat new to iOS programming
I have some code (abridged) that looks like the following
UIView *someSubView = [[UIView alloc] initWithFrame:...];
[self addSubView:someSubView];
[someSubView addTarget:self action:#selector(_handleTapOnView:) forControlEvents:UIControlEventTouchUpInside];
_tapGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(_handleTap:)];
_tapGestureRecognizer.delegate = self;
[self.view addGestureRecognizer:_tapGestureRecognizer];
Unfortunately the gesture recognizer triggers and my views addTarget call does not. I've tried commenting out the gesture recognizer code and it works, so I know its not the call to addTarget on the subview.
I solved this initially by using the gestureRecognizer:shouldReceiveTouch: and doing a hit test for the sub view, but I feel like I'm missing some fundamental understanding here that wouldn't require me adding a manual hit test.
Its important to note that I don't want the code in the _handleTap in the _tapGestureRecognizer to execute when I have tapped on my subview.
Any guidance here? Thanks!
Try using:
_tapGestureRecognizer.cancelsTouchesInView = NO;
otherwise the gesture recogniser will intercept the touches and will not forward them further (in other words, the gesture recogniser gets the touch, handles it, and since it cancel it, no other object gets the touch). By not cancelling, the touch is forwarded for any other object (recognisers or views) to handle it.
I'm displaying a document in a UIWebView. I want to place a hotspot over the document to trigger an action when it is tapped, but I also want to maintain the default UIWebView behavior of auto-zooming the document when it is double-tapped. I can't figure out how to respond to the single-taps while letting the UIWebView respond to the double-taps.
I first set up the hotspot as a transparent UIButton with an action, but double-tapping the hotspot resulted in the hotspot action being called twice. So I removed the action from the button and attached a single-tap gesture instead:
UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(singleTapAction:)];
singleTap.numberOfTapsRequired = 1;
singleTap.delegate = self;
[self.hotspot addGestureRecognizer:singleTap];
[singleTap release];
This works the same as the normal button action. But then I created a double-tap gesture, and configured it to block the single-tap gesture with requireGestureRecognizerToFail:
UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(zoomWebView:)];
doubleTap.numberOfTapsRequired = 2;
doubleTap.delegate = self;
[self.hotspot addGestureRecognizer:doubleTap];
[doubleTap release];
UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(singleTapAction:)];
singleTap.numberOfTapsRequired = 1;
[singleTap requireGestureRecognizerToFail:doubleTap];
singleTap.delegate = self;
[self.hotspot addGestureRecognizer:singleTap];
[singleTap release];
- (void)zoomWebView:(UITapGestureRecognizer *)gesture {
NSLog(#"double tap");
}
With this setup, a single-tap on the hotspot calls singleTapAction and a double-tap on the hotspot calls zoomWebView (a custom method). This is good because singleTapAction is no longer called twice, but bad because the UIWebView no longer responds to the double-tap.
I tried forwarding the double-tap event from my doubleTap gesture to the UIWebView by subclassing UITapGestureRecognizer, overriding the touchesBegan and touchesEnded methods, and sending their arguments on to the corresponding methods of the UIWebView. When I did that, I could see that my subclass was receiving the events, but the UIWebView didn't respond to the forwarded events. This is to be expected because the Event Handling Guide for iOS says that we can only forward events to custom subclasses of UIView, not to UIKit framework objects.
Is there a way to prevent my single-tap gesture from responding to double-taps that doesn't divert the double-tap events? This seems like a basic requirement, but I can't see a straightforward way to do it. I read about and experimented with UIGestureRecognizer's touch delivery properties, but no combination of values stopped the single-tap gesture from consuming the double-tap gesture.
By the way, the relationship between the hotspot and the UIWebView in my view hierarchy is that of "cousins" -- they are subviews of two sibling views. If I add the gesture recognizers to hotspot view, the web view or their "grandparent" view, I get the same results.
Okay, I found a solution in two parts:
1) I had to add my gestures to a parent view of the UIWebView. Unmatched events don't travel through overlapping objects in a view from layer to layer as I was imagining. Instead, they travel through the hierarchy of views from child to parent. So as long as I was adding my double-tap gesture to a sibling or "cousin" view of the UIWebView, it was never going to proceed on to the web view. This means that I can't use buttons or views laid out in Interface Builder to determine multiple hotspot areas. Instead, I have to redirect all single-tap events to one method and then look at the touch positions to determine what action to trigger.
2) I had to add the gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: method to my view controller (the delegate of my gestures) and return YES. This allows my single-tap gesture to respond even when I'm displaying HTML, text or image content in the UIWebView, which implements its own gesture for these content types. I learned this part from this answer.
With these changes, I understand the hierarchy of events to be:
Single-tap web view: my single-tap gesture on the web view's parent view responds; the web view's single-tap gesture also responds if applicable because simultaneous gestures are enabled
Double-tap web view: my double-tap gesture on the web view's parent view responds (but doesn't do anything); my single-tap gesture does not respond because it is configured to only respond if the double-tap fails; the web view's double-tap event also responds because it is part of the view hierarchy (it seems that the double-tap functionality of the web view does not use a gesture because otherwise it would have take precedence over my own gesture in my original setup)
With that explanation out of the way, here's some working code:
- (void)viewDidLoad {
UITapGestureRecognizer *doubleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(doubleTapWebView:)];
doubleTap.numberOfTapsRequired = 2;
doubleTap.delegate = self;
[self.webViewParent addGestureRecognizer:doubleTap];
[doubleTap release];
UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(singleTapWebView:)];
singleTap.numberOfTapsRequired = 1;
[singleTap requireGestureRecognizerToFail:doubleTap];
singleTap.delegate = self;
[self.webViewParent addGestureRecognizer:singleTap];
[singleTap release];
}
- (void)doubleTapWebView:(UITapGestureRecognizer *)gesture {
NSLog(#"double-tap");
// nothing to do here
}
- (void)singleTapWebView:(UITapGestureRecognizer *)gesture {
NSLog(#"single-tap");
CGPoint touchLocation = [gesture locationInView:self.webViewParent];
float x = touchLocation.x;
float y = touchLocation.y;
CGRect frame = self.webViewParent.frame;
if (y < frame.size.height * .33) {
NSLog(#"top");
} else if (y > frame.size.height * .67) {
NSLog(#"bottom");
} else if (x < frame.size.width * .33) {
NSLog(#"left");
} else if (x > frame.size.width * .67) {
NSLog(#"right");
} else {
NSLog(#"center");
}
}
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
return YES;
}
Always been a problem with mouse clicks since event handling began.
It's impossible at the instance of a single click, for any software to determine that a double click is about to happen.
So, if you want to handle single clicking and double clicking, you'll have to do your own double click handling.
Time the instances of single click, and generate a double click event of your own.
Hopefully that can transfer to tapping in your context.