In my iOS app have a UITableView which contains a custom subview in one of it's cells. This cell is an interactive view that handles touch events (touchesBegan, touchesEnded, touchesMoved) to update itself.
The problem is that when the user 'drags' up or down, the tableView catches these touches (although I don't pass the touches up the responder chain), scrolls the table and prevents the subview from working correctly. I would like to prevent the table from scrolling as long as the user is touching that particular subview.
The subview has no reference at all to the tableView.
How can I prevent the scrolling behavior of the table?
Update
Despite accepting the answer below, I ended up handling my situation differently. I handle the touch events in my custom view now, pass them up the responder chain (to the table cell), the cell handles the touch events as well, using them to enable/disable scrolling on the superview (the table).
Turning off "Cancellable Content Touches" in the UITableView solved this for me (in the UITableView attributes inspector under Scroll View / Touch). I got this from this SO question: Scrolling a UITableView inside a UIScrollView
From the UIScrollView:canCancelContentTouches doc:
If the value of this property is NO, the scroll view does not scroll
regardless of finger movement once the content view starts tracking.
The most common method I use in such cases is to delegate information up the event chain. Set delegates in manner:
subview->cell->table
The second thing you can do is to send a notification via Notificaion Center. Table would listen to any events that forbid normal scrolling. It is overshoot but it will leave your code consistent.
I have no more ideas at the moment.
Related
I have a scrollview where I added several buttons (dynamically, programmatically). Hence my view is totally covered with buttons. Also there are some labels
However, I observed that the uiscrollview is not scrolling when the drag starts on the button. All labels work fine. But I want this scroll to happen i.e. when drag event occurs in the uibutton, I want it to send this event to its superview (scrollview).
Please note, according to my search, subclassing the scrollview and overrriding the content touches event, or add touch began actions to uibuttons are not helpful.
How do one in general work with this event passing things when objects are added dynamically?
You have to subclass the UIScrollView, there's no other proper way, but you do not need to mess with the touch events. All you have to do is override this method
- (BOOL)touchesShouldCancelInContentView:(UIView *)view {
return YES;
}
And set the canCancelContentTouches property of the UIScrollView to YES.
I have a view controller that is basically a form with multiple UITextFields and UITextView, embedded in a UIScrollView. When an UITextField becomes first responder, the scroll view automatically move to the focused field, which is believe is the behaviour explained in the first answer in this topic :
Disable UIScrollView scrolling when UITextField becomes first responder
This does not happen when the first responder is an UITextView though, and I'm not sure why and how I should fix it.
The second problem is that when the keyboard is shown, the scroll view does not scroll if the UITextView is not in view (because it's hidden by the newly shown keyboard). I implemented the code of Apple's documentation on how to manage the keyboard :
http://developer.apple.com/library/ios/#DOCUMENTATION/StringsTextFonts/Conceptual/TextAndWebiPhoneOS/KeyboardManagement/KeyboardManagement.html
And added another activeField variable named activeView for textViews (initialized in the beginEditing of TextView, set to nil in endEditing, and scrollToVisible according to it's frame when the keyboard is shown). The problem here is that the beginEditing in UITextView is called after the keyboardWasShown, so the activeView is not initialized and thus does not scroll. For some reason, for UITextFields the beginEditing is called before, which is the intended behaviour.
How can I scroll to an UITextView and it's the first responder, and how can I move to it when the keyboard is shown and hide it?
To scroll to show anything in a UIScrollView do
scrollRectToVisible:/*frame of object you want to show*/ animated:YES
Subscribe to UITextViewTextDidBeginEditingNotification and call the above method when you get it.
I have custom UIScrollView subclass with some content views inside. In some of them I have UITapGestureRecogniser. All works fine when scroll view is not scrolling. But when it scrolling content views does not receive tap action. What is the simplest solution to handle tap action by subview while scroll view is scrolling?
Details:
MyScrollView scrolls horizontally. It contains a lot of content views (e.g. MyContentView). Each MyContentView has width about one third of MyScrollView width. So there are about 3-4 visible MyContentView elements at a moment. The main behavior of MyScrollView is to 1)make sure that after scrolling one of MyContentView elements will be at center of screen and 2)to scroll to center of MyContentView if user taps on it. So the main answer I hope to get is how to "properly" implement handling of tap action in MyContentView while MyScrollView is decelerating.
I found some same questions and answers but none of them satisfied me. The best was to implement gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer: of UITapGestureRecogniser delegate. But in this case I sometimes (when I tap, make smaaaal drag and release finger so tap is steel recognizable(lets called it quasi tap)) have both tap and scroll events and it leads to bugs for me even if scroll view is not scrolling when I begin tap. When user make quasi tap my application tries to scroll to tapped MyContentView element and than immediately handle normal scrolling. It seems even more terrible, due to some other functionality start to perform after handling tap (it must not perform when normal scrolling).
I need solution where scroll view wait enough to decide it is not tap event and only then make scroll. Otherwise if tap event had recognized scroll must not happen.
You can go with the custom delegates methods as well, using #protocol. Implement those delegate methods in view controller where your UIScrollView has been added.
like in MyContentView:
In touchesBegan method,
[self.delegate contentViewTapped:self];
Now in ContainerView class where scroll view is added, implement that method:
- (void)contentViewTapped:(MyContentView *)myContentView {
NSLog (#"ContentView no: %d", myContentView.tag); // if tag has been set while adding this view to scrollview.
}
Go through the examples for #protocol.
Hope this is what you required.
Enjoy Coding :)
This is built into UIScrollView - take a look at the delaysContentTouches and canCancelContentTouches properties. This should alleviate the problem when dragging a small bit after a tap.
This is all system built-in behaviour. I would suggest sticking with what Apple has provided for the feel of your interface (how it reacts to small drags, for instance) so that your app doesn't feel out of place on a user's phone.
EDIT:
Alternatively, you could disable scrolling of your scroll view in you gesture recognizer and re-enable it once it's ended/cancelled.
Further Edit:
I don't understand - I've created a sample project that illustrates how to intercept touches in a subview of a scroll view using gesture recognizer delegate methods. Play close attention to the "Cancellable Content Touches" and "Delays Content Touches" properties of the scroll view. They're both YES for very important reasons.
You scroll view should be delaying content touches until it has determined if the user is attempting a tap, pseudo-tap (as you put it), or a pan for the scroll view. Apple has already written the functionality you're trying to build; UIScrollView will already do what you want.
The problem is that the system doesn't want a scroll view's subviews intercepting tap events while the scroll view is scrolling. To this end, it cancels touch events if it determines that the user is actually trying to pan. Setting "Delays Content Touches" enables this behaviour. Ensure it's turned on and you should be fine.
I've made a UIScrollView the first responder. I need to maintain touch events to a -touchesEnded:withEvent: method on a view behind it. I've tried using the -nextResponder method and that failed. I've tried forwarding -touchesEnded:withEvent: to the view behind it and that fails.
How do I get this to work? The UIScrollView wont work unless it is the first responder or gets events some other way.
Thank you for any help. Shame Apple's documentation and APIs are terrible in areas.
UIScrollView handles touches in a slightly unusual way. From the class reference:
Because a scroll view has no scroll bars, it must know whether a touch signals an intent to scroll versus an intent to track a subview in the content. To make this determination, it temporarily intercepts a touch-down event by starting a timer and, before the timer fires, seeing if the touching finger makes any movement. If the timer fires without a significant change in position, the scroll view sends tracking events to the touched subview of the content view. If the user then drags their finger far enough before the timer elapses, the scroll view cancels any tracking in the subview and performs the scrolling itself...
A subview within the scroll view's content view will eventually receive non-scrolling touches to the scroll view.
A superview of a scroll view is unlikely to see touch events as its -hitTest:withEvent: will return the scroll view so touch events will be sent to the scroll view which is not required to forward them back up the responder chain to the parent view.
First responder does not influence the delivery of touch events, see http://developer.apple.com/library/ios/documentation/EventHandling/Conceptual/EventHandlingiPhoneOS/EventsiPhoneOS/EventsiPhoneOS.html#//apple_ref/doc/uid/TP40009541-CH2-SW5
The first responder is the responder object in an application (usually a UIView object) that is designated to be the first recipient of events other than touch events...
I have a UITableView which is a subview of a UIView, then that UIView is a subview of a UIScrollView. How do I detect the touches that should scroll the UITableView?
The UITableView can get item selection events (a cell in the table is selected/tapped) just fine, except that you have to hold down on the cell before it fires. But I can't get the UITableView to scroll, its always the UIScrollView that reacts to the pan gesture.
Any help is greatly appreciated. Thanks in advance!
EDIT:
Solved, though I asked the wrong question. It does work by default as Roman K pointed out. I think the problem was related to having a part of the UITableView outside the bounds of the UIScrollView (the UITableView went over the bottom bounds of the UIScrollView). Setting it to correctly fit inside the UIScrollView fixed it.
Please, make sure that UIScrollView's properties delaysContentTouches and canCancelContentTouches are set appropriately. They control how UIScrollView instance passes touch information to its subviews. By default delaysContentTouches is set to YES. Also, make sure that, if you extended UIScrollView, touchesShouldBegin:withEvent:inContentView: allow touches in the subview.
Otherwise, UITableView scrolling should work by default in your scenario. If you create a test project with just the view hierarchy as described you will see that it is the case. So, compare the two and see what difference affects the scrolling.