In Interface Builder, I've added a press gesture recognizer to a MKMapView.
An event is sent after 1 second (I am using it to add a pin to the map). I have checked the "Cancel touches in view" behavior of my gesture recognizer, but my issue is that once the long press gesture is recognized, if you keep your finger on the screen and drag it on the map view, the event (for long press) will be sent continuously while dragging, as if it was actually a drag gesture recognizer, resulting in dozens of pins being added to my map...
How can I fix this ?
Thank you.
According to the documentation:
Long-press gestures are continuous. The gesture begins
(UIGestureRecognizerStateBegan) when the number of allowable fingers
(numberOfTouchesRequired) have been pressed for the specified period
(minimumPressDuration) and the touches do not move beyond the
allowable range of movement (allowableMovement). The gesture
recognizer transitions to the Change state whenever a finger moves,
and it ends (UIGestureRecognizerStateEnded) when any of the fingers
are lifted.
With the important point highlighted.
I believe you may not be filtering the state in your gesture recognizer's delegate method.
You will need something like this:-
- (void)longPressGestureRecognizerStateChanged:(UIGestureRecognizer *)recognizer {
if (recognizer.state == UIGestureRecognizerStateBegan) {
// do your stuff...
}
}
Related
If you assign a UITapGestureRecognizer to a UIView the UIGestureRecognizerStateBegan doesn't appear when the user has touched the view.
// Tap
_tapGestureRecognizer =
[[UITapGestureRecognizer alloc] initWithTarget:self
action:#selector(tap:)];
[_someView addGestureRecognizer:_tapGestureRecognizer];
Instead the recognizer jumps straight to UIGestureRecognizerStateEnded when the user performs the tap.
I have to change that view to a UIButton and listen to the touchDown method.
_someButton = [[UIButton alloc] init];
[_someButton addTarget:self action:#selector(touchDown:) forControlEvents:UIControlEventTouchDown];
[self addSubview: _someButton];
I don't like changing the UIView to a UIButton just for this.
Can I use the UITapGestureRecognizer instead?
Let me start by saying that UITapGestureRecognizer docs clearly tell to expect a callback for all states.
For gesture recognition, the specified number of fingers must tap the view a specified number of times. Although taps are discrete gestures, they are discrete for each state of the gesture recognizer. The system sends the associated action message when the gesture begins and then again for each intermediate state until (and including) the ending state of the gesture. Code that handles tap gestures should test for the state of the gesture, for example:
func handleTap(sender: UITapGestureRecognizer) {
if sender.state == .ended {
// handling code
}
}
Hower it makes little to no sense (specially in case of single tap recognizer). You touched a view (that had the tap gesture added to it), you haven't yet lifted your finger, moved it etc. System can't know at the time of .touchDown event that this interaction is going to turn into a successful recognition of a tap (which requires lifting the finger up).
Essentially UITapGestureRecognizer (for a single touch tap) is a .touchDown + .touchUp combination. If anything else happens after .touchDown like a drag (.touchDragInside OR .touchDragExit), it may lead to successful recognition of a pan gesture (tableView scrolling etc.)
You can think of UITapGestureRecognizer roughly equivalent to .touchUpInside event for a button. A .touchUpInside event for a button doesn't call your function for .touchDown event, It is only possible to receive that event by explicitly asking for the same.
Why do the docs say so?
Maybe system is able to identify the .began state for other scenarios
a multi-tap gesture - double/triple tap (see UITapGestureReconizer.numberOfTapsRequired)
a multi-touch tap - 2/3 finger tap (see UITapGestureReconizer.numberOfTouchesRequired)
You have to test other scenarios for this if you want to know more.
I'm new to coding so I'm trying some small projects in swift. Right now, I'm trying to make a text box inside the ViewController move when the user drags it along the screen. For the text box, I am currently using a UITextField but I have no idea how to program its movement according to drag.
You'll want to add a UIPanGestureRecognizer to your view. There's all sorts of built in gesture recognizers for detecting various gestures like a tap or in this case a pan (drag). You can check them out here: https://developer.apple.com/documentation/uikit/uigesturerecognizer
Here we'll create a pan gesture recognizer, and add it to our view. Assume myView is your UITextField. A good place to do this is in your view controller's viewDidLoad() method.
let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePan(sender:)))
myView.addGestureRecognizer(pan)
The moment your finger touches the screen, we say that a touch sequence has begun. The touch sequence ends when there are no more fingers on the screen. The pan gesture will determine if this touch sequence looks like a pan, and if so, the method handlePan will be called at various stages. Here, the gesture itself will be passed into the method, which we use to determine translation and move our view accordingly. Add this as a method of your view controller.
#objc func handlePan(sender: UIPanGestureRecognizer) {
let translation = sender.translation(in: sender.view)
self.myView.center.x += translation.x
self.myView.center.y += translation.y
sender.setTranslation(CGPoint.zero, in: sender.view)
}
The first line gets the translation in the view which the gesture is attached to (myView). We then adjust myView's position based on this translation, and then we set the translation to zero. This is so that the next time this method is called, the translation will be a delta relative to the previous call.
The property sender.state will tell you the state the gesture is currently in, for example, .began, .changed, .ended. Since a pan is a continuous gesture, our method will be called many times, whenever there's a finger movement.
Is there any way that i can setup a tapGestureRecognizer in an iOS app, that either sends a signal both when an object is tapped, and when the tap is released, or setup up two tapGestureRecognizer's, one that handles the tap, and one that handles the release?
My tapGestureRecognizer is initialized like this:
let tapRecognizer = UITapGestureRecognizer(target: self, action: #selector(TapInToSubView))
tapRecognizer.numberOfTapsRequired = 1
sender.addGestureRecognizer(tapRecognizer)
Hope someone out there can help!
You need to set up a UILongPressGestureRecognizer . Set the minimumPressDuration and You can then handle the gesture state methods :
(sender.state == UIGestureRecognizerStateEnded)
(sender.state == UIGestureRecognizerStateBegan
etc. and fire your actions accordingly.
Long-press gestures are continuous. The gesture begins (began) when
the number of allowable fingers (numberOfTouchesRequired) have been
pressed for the specified period (minimumPressDuration) and the
touches do not move beyond the allowable range of movement
(allowableMovement). The gesture recognizer transitions to the Change
state whenever a finger moves, and it ends (ended) when any of the
fingers are lifted.
I have a view in an iOS application (Obj-C) which has an image view in the centre, and immediately below that a slider.
The image view shows album artwork, and the slider can be used to adjust the now-playing track position.
There is also a pair of left and right Swipe Gesture Recognizers. These are used to skip to the next or previous tracks.
The problem is that the swipe gesture recognizers seem to over-ride the users moving the slider thumb.
In my gesture recognizer code I check that the point touched was inside the image view, but it still stops the slider from being moved. (The thumb moves, but jumps back to it's original position when you remove your finger).
This is the code I use to reject the gesture if it's not inside the image view.
- (IBAction)swipeLeftGestureAction:(UISwipeGestureRecognizer *)sender {
// Get the location of the gesture.
CGPoint tapPoint = [sender locationInView:_artworkImageView];
// Make sure tap was INSIDE the artwork image frame.
if( (tapPoint.x <0)
|| (tapPoint.y < 0 )
|| (tapPoint.x > _artworkImageView.frame.size.width)
|| (tapPoint.y>_artworkImageView.frame.size.height))
{
NSLog(#"Outside!");
return;
}
NSLog(#"Swipe LEFT");
[_mediaController skipNext];
}
So my question is, how do I limit the gesture to work ONLY when swiped across the image view?
Try to put the code that restricts the gesture's area in gestureRecognizer:shouldReceiveTouch: and return NO in case you don't want the gesture to receive this touch. It should prevent the gesture from over taking the slider interaction.
If you're only interested in swipes that are inside the image view, then you should add the swipe gesture recognizer to the image view instead of adding it to your entire view. Then you won't need any special logic.
There is a dedicated method for checking if a point is inside a view
BOOL isPointInsideView = [_artworkImageViewpointInside:tapPoint withEvent:nil];
But I think what is happening is that if you will look at the tapPoint is that it actually outside of your imageView
And if your slider is really close to the imageView so the slider captures the movement, what you should do is check on the slider if it is intended for the slider and propagate on to the imageView if needed
Or inherit the UISlider and reduce its response rect
I have two UIButtons in a view (one is YES, the other NO). I now want to add a "did not answer", which would be indicated by a downward swipe on the view.
The problem is that the user may swipe down on the view, but in the process hit one of the buttons. When this happens I want to ignore the button press if there was a swipe underway. If it is just a tap on a button, the answer is recorded.
So, if the swipe occurs, I want to call the swipe gesture's action method. If it is determined no swipe occurred but one of the two buttons was touched I want to call their respective action methods. But if a button was touched in the process of a swipe, I want to call only the swipe gesture's action method.
I know there is a way but I'm wondering whether there is an EASY way of doing this. TIA for suggestions.
Since UISwipeGestureRecognizer is a "discrete" gesture, it just triggers a single action when recognized and it won't allow you to detect the end of the gesture.
So to prevent other touches during the gesture, I'd recommend using a UIPanGestureRecognizer instead since it can track your gesture from beginning to end. Then you can try setting your gesture's cancelsTouchesInView property to YES to cancel all other touches in the view that happen while that pan gesture is recognized, ex:
gesture.cancelsTouchesInView = YES;
gesture.delaysTouchesBegan = YES;
Your buttons should be registering touch up in view, so that someone who taps on the button can drag off if they decide not to proceed.
For your other swipe gesture, your buttons will not register a touch up in view during a swipe gesture, even if the swipe passes over the button or ends on it.
Okay, this seems to work. On the gesture recognizer, I used:
UISwipeGestureRecognizer *swipeDown = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(didSwipeDown:)];
swipeDown.direction = UISwipeGestureRecognizerDirectionDown;
swipeDown.delaysTouchesBegan = YES;
swipeDown.delegate = self;
[self addGestureRecognizer:swipeDown];
They delaysTouchesBegan = YES allows it to determine whether the swipe has occurred before passing the touches on to the buttons. So, if you swipe, it calls the swipe GR, and if you touch either button, you get that. Thanks for your answers...