Issues with UIScrollView and touchesBegan - ios

When a user touches one of the white UIViews, it runs its touchesBegan:
...
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
delegate.startedTouchingPage(page: self)
...
The delegate is the VC. startedTouchingPage is implemented in the VC as
func startedTouchingPage(page: Page) {
if (page.tool == .PEN || page.tool == .ERASER) {
scrollView.isScrollEnabled = false
scrollView.panGestureRecognizer.isEnabled = false
}
}
I thought this would prevent scrolling and panning, and allow the pen to draw in peace. But instead, when I try to draw on the page, the pen sometimes draws properly, and sometimes instead scrolls the page.
It turns out that the times that the page scrolls instead of draws, touchesBegan didn't run, and thus startedTouchingPage didnt run either. I can't figure out why...

Related

UIButton touchDragEnter and touchDragExit called too often

How can I avoid a UIButtons .touchDragEnter and .touchDragExit functions from rapid firing? This question demonstrates the issue perfectly, but the only answer does not describe how to work around it. I'm trying to animate a button when the users finger on the button, and animate it again when their finger slides off. Are there any better ways to do this? If not, how should I stop my animation code from firing multiple times when the users finger is right between an .enter and an .exit state?
You could instead track the location of the touch point itself and determine when the touch point moves in and out of the button
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
let point = t.location(in: self)
// moving in to the button
if button.frame.contains(point) && !wasInButton {
// trigger animation
wasInButton = true
}
// moving out of the button
if !button.frame.contains(point) && wasInButton {
// trigger animation
wasInButton = false
}
}
}
wasInButton could be a boolean variable set to true when there is a touch down in the button's frame:
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
let point = t.location(in: self)
if button.frame.contains(point) {
wasInButton = true
// trigger animation
} else {
wasInButton = false
}
}
This would require you to subclass the button's superview. And since you might not want to animate as soon as the point leaves the button's frame (because the user's finger or thumb would still be covering most of the button), you could instead do the hit test in a larger frame that encapsulates your button.

UIButtons in specific zone of the screen make delay on Touch Down event

I'm creating a Custom Keyboard for iOS. I have 4 rows of keys, each key have two actions: Touch Down to highlight button, and Touch Up Inside to unhighlight the button in 0.4 seconds.
But at the left edge of the screen there is a zone where Touch Down event of any button makes a delay for about quarter of second to show highlight.
See the image
So to see highlighted version, I had to hold the button, or swipe right from it. The buttons are the same, no difference at all. When I switch from letters to symbols, this left edge zone also makes the same delay. I've tried to move all the keys to the right, about 20px, and they worked fine, without delay. Ok, stick to the edge back, and delay came back also. Then I noticed, that pressing the button on its right edge, about 1-2 pixels made no delay at all. So, it seems like the problem is in this left side edge zone of the screen particularly.
By the way, I am running this app on my 5S, I've tried to run it on my friend's 5C, the same problem. But when I run it in the simulator, there is no such delay.
Use new iOS 11 feature to solve this problem definitely.
var preferredScreenEdgesDeferringSystemGestures: UIRectEdge { get }
Documentation
I'm too creating a custom keyboard, and as far as I understand, that happens due to preferredScreenEdgesDeferringSystemGestures not working properly when overridden inside UIInputViewController, at least on iOS 13.
When you override this property in a regular view controller, it works as expected:
override var preferredScreenEdgesDeferringSystemGestures: UIRectEdge {
return [.left, .bottom, .right]
}
That's however not the case for UIInputViewController.
UPD: It appears, gesture recognizers will still get .began state update, without the delay. So, instead of following the rather messy solution below, you can add a custom gesture recognizer to handle touch events.
You can quickly test this adding UILongPressGestureRecognizer with minimumPressDuration = 0 to your control view.
Another solution:
My original workaround was calling touch down effects inside hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView?, which is called even when the touches are delayed for the view.
You have to ignore the "real" touch down event, when it fires about 0.4s later or simultaneously with touch up inside event. Also, it's probably better to apply this hack only in case the tested point is inside ~20pt lateral margins.
So for example, for a view with equal to screen width, the implementation may look like:
let edgeProtectedZoneWidth: CGFloat = 20
override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
let result = super.hitTest(point, with: event)
guard result == self else {
return result
}
if point.x < edgeProtectedZoneWidth || point.x > bounds.width-edgeProtectedZoneWidth
{
if !alreadyTriggeredFocus {
isHighlighted = true
}
triggerFocus()
}
return result
}
private var alreadyTriggeredFocus: Bool = false
#objc override func triggerFocus() {
guard !alreadyTriggeredFocus else { return }
super.triggerFocus()
alreadyTriggeredFocus = true
}
override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
super.touchesCancelled(touches, with: event)
alreadyTriggeredFocus = false
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
super.touchesEnded(touches, with: event)
alreadyTriggeredFocus = false
}
...where triggerFocus() is the method you call on touch down event. Alternatively, you may override touchesBegan(_:with:).

iOS: Why touchesBegan has some delay in some specific area in UIView

I'm making a custom keyboard and I'm in a really weird situation.
I've noticed that when I catch the event touchesBegan at the rear left (about 20 pixels) of the UIView (inputView), I'll have some delay in here.
Any action I do in touchesBegan will be perform slower than other area.
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?)
{
self.keypop.hidden = false
}
override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
{
self.keypop.hidden = true
}
And this trouble affects my app's performance.
In this example, I will not see the keypop appears when I touched on the rear left because self.keypop.hidden was delayed in showing up.
I don't know why, or is this an error from iOS 9?
I've been stuck on this trouble for a week.
In my situation I was using touchBegan in a CollectionView and it was delaying touches when I tap
Its worked with me by simply added this code
In Swift,
self.collectionView.delaysContentTouches = false
/*delaysContentTouches applies to all UIScrollView instances.*/
The answer here seems to have fixed the same issue in our keyboard:
UISystemGateGestureRecognizer and delayed taps near bottom of screen
With the following code:
override func viewDidAppear(animated: Bool) {
let window = view.window!
let gr0 = window.gestureRecognizers![0] as UIGestureRecognizer
let gr1 = window.gestureRecognizers![1] as UIGestureRecognizer
gr0.delaysTouchesBegan = false
gr1.delaysTouchesBegan = false
}

Touch events are delayed near left screen edge on iOS 9 only. How to fix it?

I am developing a keybaord extension for iOS. On iOS 9 the keys react imediatelly except for keys along left edge of the keyboard. Those react with around 0.2 second delay. The reason is that the touches are simply delivered with this delay to the UIView that is root view of my keyboard. On iOS 8 there is no such delay.
My guess is that this delay is cause by some logic that is supposed to recognize gesture for opening "running apps screen". That is fine but the delay on a keyboard is unacceptable. Is there any way how to get those events without delay? Perhaps just setting delaysTouchesBegan to false on some UIGestureRecognizer?
This is for anyone using later versions of iOS (this is working on iOS 9 and 10 for me). My issue was caused by the swipe to go back gesture interfering with my touchesBegan method by preventing it from firing on the very left edge of the screen until either the touch was ended, or the system recognised the movement to not be that of the swipe to go back gesture.
In your viewDidLoad function in your controller, simply put:
self.navigationController?.interactivePopGestureRecognizer?.delaysTouchesBegan = false
The official solution since iOS11 is overriding preferredScreenEdgesDeferringSystemGestures of your UIInputViewController.
https://developer.apple.com/documentation/uikit/uiviewcontroller/2887512-preferredscreenedgesdeferringsys
However, it doesn't seem to work on iOS 13 at least. As far as I understand, that happens due to preferredScreenEdgesDeferringSystemGestures not working properly when overridden inside UIInputViewController, at least on iOS 13.
When you override this property in a regular view controller, it works as expected:
override var preferredScreenEdgesDeferringSystemGestures: UIRectEdge {
return [.left, .bottom, .right]
}
That' not the case for UIInputViewController, though.
UPD: It appears, gesture recognizers will still get .began state update, without the delay. So, instead of following the rather messy solution below, you can add a custom gesture recognizer to handle touch events.
You can quickly test this adding UILongPressGestureRecognizer with minimumPressDuration = 0 to your control view.
Another solution:
My original workaround was calling touch down effects inside hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView?, which is called even when the touches are delayed for the view.
You have to ignore the "real" touch down event, when it fires about 0.4s later or simultaneously with touch up inside event. Also, it's probably better to apply this hack only in case the tested point is inside ~20pt lateral margins.
So for example, for a view with equal to screen width, the implementation may look like:
let edgeProtectedZoneWidth: CGFloat = 20
override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
let result = super.hitTest(point, with: event)
guard result == self else {
return result
}
if point.x < edgeProtectedZoneWidth || point.x > bounds.width-edgeProtectedZoneWidth
{
if !alreadyTriggeredFocus {
isHighlighted = true
}
triggerFocus()
}
return result
}
private var alreadyTriggeredFocus: Bool = false
#objc override func triggerFocus() {
guard !alreadyTriggeredFocus else { return }
super.triggerFocus()
alreadyTriggeredFocus = true
}
override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
super.touchesCancelled(touches, with: event)
alreadyTriggeredFocus = false
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
super.touchesEnded(touches, with: event)
alreadyTriggeredFocus = false
}
...where triggerFocus() is the method you call on touch down event. Alternatively, you may override touchesBegan(_:with:).
If you have access to the view's window property, you can access these system gesture recognizers and set delaysTouchesBegan to false.
Here's a sample code in swift that does that
if let window = view.window,
let recognizers = window.gestureRecognizers {
recognizers.forEach { r in
// add condition here to only affect recognizers that you need to
r.delaysTouchesBegan = false
}
}
Also relevant: UISystemGateGestureRecognizer and delayed taps near bottom of screen

iOS UIPanGestureRecognizer: adjust sensitivity?

My question: Is there a way to adjust the "sensitivity" of UIPanGestureRecognizer so that it turns on 'sooner', i.e. after moving a fewer number of 'pixels'?
I have a simple app with a UIImageView, and pinch and pan gesture recognizers tied to this so that the user can zoom in and draw on the image by hand. Works fine.
However, I notice the stock UIPanGestureRecognizer doesn't return a value of UIGestureRecognizerState.Changed until the user's gesture has moved about 10 pixels.
Example: Here's a screenshot showing several lines that I've attempted to draw shorter & shorter, and there is a noticeable finite length below which no line gets drawn because the pan gesture recognizer never changes state.
IllustrationOfProgressivelyShorterLines.png
...i.e., to the right of the yellow line, I was still trying to draw, and my touches were being recognized as touchesMoved events, but the UIPanGestureRecognizer wasn't firing its own "Moved" event and thus nothing was getting drawn.
(Note/clarification: That image takes up the entirety of my iPad's screen, so my finger is physically moving more than an inch even in the cases where no state change occurs to the recognizer. It's just that we're 'zoomed in' in terms of the tranformation generated by the pinch gesture recognizer, so a few 'pixels' of the image take up a significant amount of the screen.)
This is not what I want. Any ideas on how to fix it?
Maybe some 'internal' parameter of UIPanGestureRecognizer I could get at if I sub-classed it or some such? I thought I'd try to sub-class the recognizer in a manner such as...
class BetterPanGestureRecognizer: UIPanGestureRecognizer {
var initialTouchLocation: CGPoint!
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent) {
super.touchesBegan(touches, withEvent: event)
initialTouchLocation = touches.first!.locationInView(view)
print("pan: touch begin detected")
print(self.state.hashValue) // this lets me check the state
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent) {
super.touchesMoved(touches, withEvent: event)
print("pan: touch move detected")
print(self.state.hashValue) // this remains at the "began" value until you get beyond about 10 pixels
let some_criterion = (touches.first!.isEqual(something) && event.isEqual(somethingElse))
if (some_criterion) {
self.state = UIGestureRecognizerState.Changed
}
}
}
...but I'm not sure what to use for some_criterion, etc.
Any suggestions?
.
Other alternatives that could work, but that I'd rather not have to do:
I could simply attach my UIPanGestureRecognizer to some parent,
non-zoomed view, and then use affine transforms & such to remap the
points of the pan touches onto the respective parts of the image.
So why am I not doing that? Because the code is written so that
lots of other objects hang off the image view and they all get the
same gesture recognizers and....everything works just great without
my having keep track of anything (e.g. affine transformations), and the problem only shows up if you're really-really zoomed in.
I could abandon UIPanGestureRecognizer, and effectively just write my own using touchesBegan and touchesMoved (which is kind of
what I'm doing), however I like how UIPanGestureRecognizer
differentiates itself from, say, pinch events, in a way that I don't
have to worry about coding up myself.
I could just specify some maximum zoom beyond which the user can't go. This fails to implement what I'm going for, i.e. I want to allow for fine-detail level of manipulation.
Thanks.
[Will choose your answer over mine (i.e., the following) if merited, so I won't 'accept' this answer just yet.]
Got it. The basic idea of the solution is to change the state whenever touches are moved, but use the delegate method regarding simultaneous gesture recognizers so as not to "lock" out any pinch (or rotation) gesture. This will allow for one- and/or multi-fingered panning, as you like, with no 'conflicts'.
This, then, is my code:
class BetterPanGestureRecognizer: UIPanGestureRecognizer, UIGestureRecognizerDelegate {
var initialTouchLocation: CGPoint!
override init(target: AnyObject?, action: Selector) {
super.init(target: target, action: action)
self.delegate = self
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent) {
super.touchesBegan(touches, withEvent: event)
initialTouchLocation = touches.first!.locationInView(view)
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent) {
super.touchesMoved(touches, withEvent: event)
if UIGestureRecognizerState.Possible == self.state {
self.state = UIGestureRecognizerState.Changed
}
}
func gestureRecognizer(_: UIGestureRecognizer,
shouldRecognizeSimultaneouslyWithGestureRecognizer:UIGestureRecognizer) -> Bool {
if !(shouldRecognizeSimultaneouslyWithGestureRecognizer is UIPanGestureRecognizer) {
return true
} else {
return false
}
}
}
Generally setting that "shouldRecognizeSimultaneouslyWithGestureRecognizer" delegate to true always is what many people may want. I make the delegate return false if the other recognizer is another Pan, just because I was noticing that without that logic (i.e., and making the delegate return true no matter what), it was "passing through" Pan gestures to underlying views and I didn't want that. You may just want to have it return true no matter what. Cheers.
Swift 5 + small improvement
I had a case when accepted solution conflicted with basic taps on toolbar which also had this betterPanGesture so I added minimum horizontal offset parameter to trigger state changing to .changed
class BetterPanGestureRecognizer: UIPanGestureRecognizer {
private var initialTouchLocation: CGPoint?
private let minHorizontalOffset: CGFloat = 5
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
super.touchesBegan(touches, with: event)
self.initialTouchLocation = touches.first?.location(in: self.view)
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
super.touchesMoved(touches, with: event)
if self.state == .possible,
abs((touches.first?.location(in: self.view).x ?? 0) - (self.initialTouchLocation?.x ?? 0)) >= self.minHorizontalOffset {
self.state = .changed
}
}
}

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