Touch event handled by multiple views - ios

I have a subclass of UIView on top of a UITableView. I am using the UITableView to display some data and, at the same time, I would like to overlay an animation that follows the finger (for instance, leaving a trail).
If I get it right, I need the touch events to be handled both by the UIView subclass and the UITableView. How can I do that?
Is it possible to have, ie, touchesMoved being triggered on the UIView subclass and then on UITableView?
Thank you so much for any help.

The way I have solved this problem is in a way that is not that clean, but it works. Please let me know if there's a better way to do this.
I have overridden hitTest for my custom UIView so that it directs touches to the UITableView underneath. Then in the UITableView I am handling the gestures through touchesBegan, touchesMoved, etc. There I am also calling touchesBegan on the UIView.
In this way touches are handled by two views.
The reason why I am not doing the other way around (having UIView's touchesBegan calling UITableView's touchesBegan) is that gestures recognizers on the UITableView would not work.
UIView subclass' hitTest
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
// tview is the UITableView subclass instance
CGPoint tViewHit = [tView convertPoint:point fromView:self];
if ([tView pointInside:tViewHit withEvent:event]) return tView;
return [super hitTest:point withEvent:event];
}
UITableView subclass's touchesBegan
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint location = [touch locationInView:touch.view];
// ....
// view is the UIView's subclass instance
[view touchesBegan:touches withEvent:event];
}

No, you cann't do it implicity. Event Delivery chapter says
The window object uses hit-testing and the responder chain to find the
view to receive the touch event. In hit-testing, a window calls
hitTest:withEvent: on the top-most view of the view hierarchy; this
method proceeds by recursively calling pointInside:withEvent: on each
view in the view hierarchy that returns YES, proceeding down the
hierarchy until it finds the subview within whose bounds the touch
took place. That view becomes the hit-test view.
So, when window finds touched view it returns YES. Only one view can handle touches at the current moment.
But if you need to handle event for UITableView then handle it for UIView! You can convert touched point to required coordinates with – convertPoint, – convertRect functions, add subview to UITableView and move it depends on coordinate, and a lot of another things.

UITableView relays unhandled touch events to UIView. (Google "responder chain")
UITableView Documentation
So, you can handle your touch events in UIView only. So. In your UIView
touchesstart - do initialization stuff
touchesmove - draw tail on UIView (Use timers/delayedresponse to desable points so that it would look like a trail)
touchesend - do remaining stuff
Hope this helps.

Related

How to make the subview outside the bounds recognize the touches

I have a view with a subview. When a button in the subview is tapped, the subview expands outside the bounds of a view, presenting couple of other buttons. However, I cannot find a way to interact with them.
I found a code at Apple's site:
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
// Convert the point to the target view's coordinate system.
// The target view isn't necessarily the immediate subview
CGPoint pointForTargetView = [self.targetView convertPoint:point fromView:self];
if (CGRectContainsPoint(self.targetView.bounds, pointForTargetView)) {
// The target view may have its view hierarchy,
// so call its hitTest method to return the right hit-test view
return [self.targetView hitTest:pointForTargetView withEvent:event];
}
return [super hitTest:point withEvent:event];
}
However, I cannot understand how should I use it, so that my subview will recognize the touches.
Any help would be greately appreciated.
You need to subclass the UIView or which ever class you need and override that method. Then create an object of that subclass and use it. It will then recognize the touches.

UITableViewCell should stop Forwarding Touch Events to ScrollView

i have a custom UITableViewCell with a DrawingView as a subview. if the user try to draw something on that view everytime the touch events are forwarded to the underlying ScrollView (UITableView) and than the view scrolls. How can i disable the forwarding from the touch/scroll-events to the scrollView, that the user can draw on the DrawingView?
Any idear's? I tests the exclusiveTouch property, methods like hitTest or touchBegan to captcher the events and stop the scrolling, but nothing helped. Thanks for helping!
The caveat here is that a 'drawing' motion could very easily be interpreted as a scrolling motion.
What you need to do is override pointInside on your cell.
Effectively:
- (BOOL)pointInside:(CGPoint)point
withEvent:(UIEvent *)event
{
if (CGRectContainsPoint(drawingView.frame, point)) {
// Use the point to do the drawing
[drawingView drawAtPoint:point];
// Disable scrolling for good measure
self.tableView.scrollView.scrollEnabled = NO;
return NO;
}
// Enable scrolling
self.tableView.scrollView.scrollEnabled = YES;
return [super pointInside:point withEvent:event];
}
What this means is that as long as the user touches your cell inside the drawingView, scrolling won't happen.
If you're looking to scroll and draw at the same time from within the drawingView, that's going to be a lot kludgier to pull off.
See if this works. You may have to do some extra work like forwarding the point to your drawingView to draw something at the point.
Be careful that even if your finger is touching the same point, the pointInside method could be called multiple times so take care of duplicate events being called.

UIView handle and pass touch events to next sibling view

I'm building an iOS app that has a custom UIView upon a UIScrollView which in turn has a subview.
Here's the layout structure:
Note that the custom UIView(called "Detected Object Hint View") is not a subview of ScrollView, it's a sibling view of UIScrollView. And I want to respond to tap gesture on the custom UIView, so I've added UITapGestureRecognizer to the UIView, and it works for tap, but the UIScrollView will never get any touch events (not responding to scroll or zoom gesture).
I've googled a while, and a lot of people pointed out that in order for other view to respond to the touch events, I should implement the following method:
- (id)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
UIView *hitView = [super hitTest:point withEvent:event];
if (hitView == self){
return nil;
}
else {
return hitView;
}
}
But once I've added this method to my custom UIView, it will not respond to tap gesture either (of course).
So I'm wondering how can I handle the tap gesture on my custom UIView and pass the touch events to UIScrollView as well?
Big thanks!

touchesBegan in custom UITableViewCell, touchesEnded in UIView

I am trying to mimic a drag n drop of an image from a UITableView to a UIView. Both the UITableView and UIView are on the same view, side by side.
My approach:
is to fire the touchesBegan event inside the UITableView (i.e. when a cell is touched/selected) and fire the touchesEnded event when the touch ends in the UIView.
The problem:
So I created a custom UITableViewCell that contains a UIImageView and a couple of UILabels. And I set the User Interaction Enabled for this UIImageView. Then to receive the touchesBegan event, I did override the touchesBegan method inside the custom UITableViewCell class; and now I am able to receive the touchesBegan event from the cell.
The problem is
I am not getting the touchesEnded event when the touch ends on the UIView. Note that I already implemented the touchesEnded method inside the view controller class (not in the custom class); and if I start and stop a touch within this UIView, I see the touchesEnded being fired.
Is there anything I am missing here?
Using Xcode 4.6 (4H127), testing on iPad 2 with iOS 6.1.3
This will not work that way. You will need to utilize the touch methods on the parent view that contains both of your subviews. Could look abstractly like this:
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
if ([self touchOnCell:touches]) { //check to see if your touch is in the table
isDragging = YES; //view cell
}
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
//do your dragging code here
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
if (isDragging && [self touchOnDropView:touches]) {
//do your drop code here
}
}
now if this doesnt work like that alone you might want to implement the hitTest on the tableView and if the touch is in the dragging object's region, then return the parent view.
hope this helps

Allow UIScrollView and its subviews to both respond to a touch

I want both my UIScrollView and its subviews to receive all touch events inside the subview. Each can respond in its own way.
Alternatively, if tap gestures were forwarded to subviews, all would be well.
A lot of people are struggling in this general area. Here are a few of the many related questions:
How does UIScrollView steal touches from its subviews
How to steal touches from UIScrollView?
How to Cancel Scrolling in UIScrollView
Incidentally, if I override hitTest:withEvent: in the scroll view, I do see the touches as long as userInteractionEnabled is YES. But that doesn't really solve my problem, because:
1) At that point, I don't know if it's a tap or not.
2) Sometimes I need to set userInteractionEnabled to NO.
EDIT: To clarify, yes, I want to treat taps differently from pans. Taps should be handled by subviews. Pans can be handled by the scroll view in the usual way.
First, a disclaimer. If you set userInteractionEnabled to NO on the UIScrollView, no touch events will be passed to the subviews. So far as I'm aware, there's no way around that with one exception: intercept touch events on the superview of the UIScrollView, and specifically pass those events to the subviews of UIScrollView. To be honest, though, I don't know why you would want to do this. If you're wanting to disable specific UIScrollView functionality (like...well, scrolling) you can do that easily enough without disabling UserInteraction.
If I understand your question, you need tap events to be processed by the UIScrollView and passed to the subviews? In any case (whatever the gesture is), I think what you're looking for is the protocol method gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: in the protocol UIGestureRecognizerDelegate. In your subviews, whatever gesture recognizers you have, set a delegate (probably whatever class is setting the UIGestureReconginzer in the first place) on the gesture recognizer. Override the above method and return YES. Now, this gesture will be recognized along with any other recognizers that might have 'stolen' the gesture (in your case, a tap). Using this method you can even fine tune your code to only send certain kinds of gestures to the subviews or send the gesture only in certain situations. It gives you a lot of control. Just be sure to read about the method, especially this part:
This method is called when recognition of a gesture by
either gestureRecognizer or otherGestureRecognizer would block the
other gesture recognizer from recognizing its gesture. Note that
returning YES is guaranteed to allow simultaneous recognition;
returning NO, on the other hand, is not guaranteed to prevent
simultaneous recognition because the other gesture recognizer's
delegate may return YES.
Of course, there's a caveat: This only applies to gesture recognizers. So you may still have problems if you're trying to use touchesBegan:, touchesEnded, etc to process the touches. You can, of course, use hitTest: to send raw touch events on to the subviews, but why? Why process the events using those methods in UIView, when you can attach a UIGestureRecognizer to a view and get all of that functionality for free? If you need touches processed in a way that no standard UIGestureRecognizer can provide, subclass UIGestureRecognizer and process the touches there. That way you get all the the functionality of a UIGestureRecognizer along with your own custom touch processing. I really think Apple intended for UIGestureRecognizer to replace most (if not all) of the custom touch processing code that developers use on UIView. It allows for code-reuse and it's a lot easier to deal with when mitigating what code processes what touch event.
I don't know if this can help you, but I had a similar problem, where I wanted the scrollview to handle double-tap, but forward single tap to subviews. Here is the code used in a CustomScrollView
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch* touch = [touches anyObject];
// Coordinates
CGPoint point = [touch locationInView:[self.subviews objectAtIndex:0]];
// One tap, forward
if(touch.tapCount == 1){
// for each subview
for(UIView* overlayView in self.subviews){
// Forward to my subclasss only
if([overlayView isKindOfClass:[OverlayView class]]){
// translate coordinate
CGPoint newPoint = [touch locationInView:overlayView];
//NSLog(#"%#",NSStringFromCGPoint(newPoint));
BOOL isInside = [overlayView pointInside:newPoint withEvent:event];
//if subview is hit
if(isInside){
Forwarding
[overlayView touchesEnded:touches withEvent:event];
break;
}
}
}
}
// double tap : handle zoom
else if(touch.tapCount == 2){
if(self.zoomScale == self.maximumZoomScale){
[self setZoomScale:[self minimumZoomScale] animated:YES];
} else {
CGRect zoomRect = [self zoomRectForScrollView:self withScale:self.maximumZoomScale withCenter:point];
[self zoomToRect:zoomRect animated:YES];
}
[self setNeedsDisplay];
}
}
Of course, the effective code should be changed, but at this point you should have all the informations you need to decide if you have to forward the event. You might need to implement this in another method as touchesMoved:withEvent:.
Hope this can help.
I was having this same problem, but with a scrollview that was inside UIPageViewController, so it had to be handled slightly differently.
By changing the cancelsTouchesInView property to false for each recognizer on the UIScrollView I was able to receives touches to buttons inside the UIPageViewController.
I did so by adding this code into viewDidLoad:
guard let recognizers = self.pageViewController.view.subviews[0].gestureRecognizers else {
print("No gesture recognizers on scrollview.")
return
}
for recognizer in recognizers {
recognizer.cancelsTouchesInView = false
}
If what you need is to differ between a touch and a scroll then you can test if touches has been moved. If this is a tap then touchHasBeenMoved will not be called then you can assume this is a touch.
At this point you can set a boolean to indicate if a movnent accoured and set this Boolean as a condition in your other methods.
I am on the road but if that's what you need I will be able to explain better later.
A hackish way to achieve your objective - not 100% exact - is to subclass the UIWindow and override the - (void)sendEvent:(UIEvent *)event;
A quick example:
in SecondResponderWindow.h header
//SecondResponderWindow.h
#protocol SecondResponderWindowDelegate
- (void)userTouchBegan:(id)tapPoint onView:(UIView*)aView;
- (void)userTouchMoved:(id)tapPoint onView:(UIView*)aView;
- (void)userTouchEnded:(id)tapPoint onView:(UIView*)aView;
#end
#interface SecondResponderWindow : UIWindow
#property (nonatomic, retain) UIView *viewToObserve;
#property (nonatomic, assign) id <SecondResponderWindowDelegate> controllerThatObserves;
#end
in SecondResponderWindow.m
//SecondResponderWindow.m
- (void)forwardTouchBegan:(id)touch onView:(UIView*)aView {
[controllerThatObserves userTouchBegan:touch onView:aView];
}
- (void)forwardTouchMoved:(id)touch onView:(UIView*)aView {
[controllerThatObserves userTouchMoved:touch onView:aView];
}
- (void)forwardTouchEnded:(id)touch onView:(UIView*)aView {
[controllerThatObserves userTouchEnded:touch onView:aView];
}
- (void)sendEvent:(UIEvent *)event {
[super sendEvent:event];
if (viewToObserve == nil || controllerThatObserves == nil) return;
NSSet *touches = [event allTouches];
UITouch *touch = [touches anyObject];
if ([touch.view isDescendantOfView:viewToObserve] == NO) return;
CGPoint tapPoint = [touch locationInView:viewToObserve];
NSValue *pointValue = [NSValue valueWithCGPoint:tapPoint];
if (touch.phase == UITouchPhaseBegan)
[self forwardTouchBegan:pointValue onView:touch.view];
else if (touch.phase == UITouchPhaseMoved)
[self forwardTouchMoved:pointValue onView:touch.view];
else if (touch.phase == UITouchPhaseEnded)
[self forwardTouchEnded:pointValue onView:touch.view];
else if (touch.phase == UITouchPhaseCancelled)
[self forwardTouchEnded:pointValue onView:touch.view];
}
It's not 100% conforms to what your were expecting - because your second responder view does not handle the touch event natively via -touchDidBegin: or so, and has to implement the SecondResponderWindowDelegate. However this hack does allow you to handle touch events on additional responders.
This method is inspired by and extended from MITHIN KUMAR's TapDetectingWindow

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