Implementing a sort of 'distress call' button which should work as following:
User starts application and covers a screen with a palm of a hand
Some time passes, user may introduce additional touches during that time or remove some of the existing (but not all of them), location/shape of touches may change
When user releases a hand (i.e. removes last touch) a distress signal is emitted by the app
Basically, the app should register two events: (1) a screen is touched (2) all touched are released
I'm trying to use touchesBegan/touchesEnded methods and those work for small area touches (fingertips) but on touching screen with a full palm or even only palm edge a touchesCancelled gets triggered immediately while hand is still on the screen. Obviously no other events are emitted upon hand release afterwards.
I tried subclassing UIWindow and UIApplication and overriding sendEvent in those but got no additional info - large area touches are triggering touch begin and immediately touch cancel, releasing hand afterwards emits nothing. In some cases large area touches fire no events at all, not even the touchesBegan. Basically, iOS doesn't let me work with a very basic scenario - detecting just the fact of screen touch/release.
Is there any way to query the screen touch state directly and not work with responder chain? Or suppress the cancellation event from firing? Or maybe I'm missing something?
Unfortunately, as of right now, no solution exists
Related
3D touch seems really cool and I wanted to see how it would work in a musical context. I was reading a bit about 3D touch and it seems like the force property almost always reads as 0 when a touch begins (touchesBegan method).
How do I get a usable force when a touch begins because even if I'm pressing with maximum "force" I'm still getting that initial 0? I was thinking about just approximating a value within a time frame but that would involve me moving the touch. I just want a usable force upon the first touch.
Thanks!
Unfortunately this is impossible.
Every touch starts as a contact with no force at all, as soon as the user's finger makes contact (or even near-contact) with the screen. The force only starts to build as the user's finger is compressed against the screen.
The only way for touchesBegan: to report any force at all would be for it to delay artificially for a certain number of milliseconds before reporting a touch, to allow the force to build up. This would destroy the interactivity of all iOS applications; and Apple put a huge amount of work into delivering a touch the instant it is detected.
I'm testing the touch detection capabilities of the iPad (specifically iPad 3 at the moment). I'm printing out a log of detected touches to see what is going on, and using a bottle with three foam (touch friendly) pads at the bottom.
The touches are detected fine and it logs any slight movements which is great. The issue is that after a while if the bottle isn't moved at all, all three touches are forcibly cancelled and remain undetected until the bottle is removed and placed back down.
So it seems there's a timeout on these touches... I have not found any specific information on this. Is there any way to revive or keep alive touches without having to physically remove and restore your touch points?
A capacitive touch sensor is a very sensitive instrument, and a lot of filtering is done before the OS reports touches to you. This is also the reason why the iPad cannot detect touches with smaller contact areas than what comes with cheap styli - rubber domes of about 7mm diameter. The touchscreen controller detects smaller touches alright, but filters them to avoid spurious signals. Note that the touchscreen of a Samsung Galaxy will already detect touches with a dull pencil - the screen is (for practical purposes) the same as that of an iPad, but the cutoff for the controller is lower.
I would expect that the self-calibrating logic inside the touch controller will calibrate your touches away. Basically, it will set the signal produced by your foam pads as the new normal. On the application side there is nothing that you can do to reverse this.
Disclaimer: I have no inside knowledge of what goes on inside the touchscreen controller. My answer is based on much reading and solid reasoning, nothing more.
I need to track if the user is touching the screen across multiple views and separate screens throughout my app. I have already created a window delegate method to receive every type of touch event. The problem is that if I keep one finger on the first screen and tap a button with a separate finger that takes me to the second screen, when I release my original finger no event is fired.
This problem is the same if you were to hold your finger on the screen before the app loads and then release it once it's started, no event is fired for the touch ending.
I presume there is some in built system in iOS that states you have to start a new touch once the app has started or the screen/view has changed, so if you release a finger that was already touching nothing happens.
Is there a way to detect this? I really need to keep a constant accurate number of touches on the screen throughout the different screens/views within my app, especially if the user takes their finger(s) off the screen.
On Mac, one can always get the location of the mouse "outside the event stream" (ie, even if you've not subscribed to any delegate methods for mouseUp: et al) by calling [NSEvent mouseLocation].
Is there any way on iOS to get current touch events without listening to touchesBegan:?
I ask because there is at least one situation in which touchesBegan is not called: at app launch, if a touch is already in progress, touchesBegan is never called. In fact, neither are any of the touch-related UIEvent methods called as near as I can tell (nor UIApplication's / UIWindow's sendEvent:, apparently).
I would like to vary the behavior of my app slightly based on whether a touch is in progress at launch. Is there any way to detect an in-progress touch at app launch?
This cannot be done. The simple reason: The touch events don't belong to your app. Each touch belongs to some UI element (or responder). As you already know, this element gets the began, moved, ended, cancelled messages.
This is even true within a properly programmed app: All events regarding one touch are delivered to the very same object. After all, how would another object know what to do with that event, and how should the first object properly finish its expected behavior?
While you can (or could, but probably shouldn't) find a work around within your app, there's just no way for cross-app-touch passings.
And on the Mac you may query the mouse position, but in normal application flow there'll always be a mouse down before you get a mouse up event.
To be honest, I don't see any reason why this would be needed anyway... oh wait... I could split my app icon into several areas... not sure if it would already break privacy laws, though, if you get to know where the user has his icon on screen.
I think you could simply "extend" the application launch. When I had time consuming tasks during my application launch, I used to show the same splash screen with a UIActivityIndicator while the action was being carried out.
You could simply create a NSTimer, wait for about 2 seconds and during this time, check for touches, while the splash screen will still be showing.
To do this, in applicationDidFinishLaunch, push a ViewController that looks exactaly like the splash screen and check for touches in this ViewController. After those 2 seconds, proceed with normal initialisation. This behaviour also helps if you have time consuming tasks during initialisation.
I know, it`s a workaround, but my guess, is that it is not possible to check for touches because application will be working on the main thread and the touches also processes on the main thread. This could happen also because there are no ViewControllers or UIWindow initialised and ready to listen to touches.
Hope it helps.
You might try handling the hitTest:withEvent: instead.
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event;
Since according to apple doc "Returns the farthest descendant of the receiver in the view hierarchy (including itself) that contains a specified point."
I'm working on a game, and I'm using a CAEAGLLayer backed UIView subclass to present the game engine. Touch handling is done using -touchesBegan:withEvent: et. al.
Everything works fine, except that very rarely, if one of the on-screen controls is tapped rapidly, -touchesBegan:withEvent: doesn't get called for somewhere between 0.1 and 1-2 seconds. This happens maybe one in 20 times, and only if you tap the screen rapidly (4-5 times) first. It seems to be more likely to happen if I am also holding down another finger on a different control on the screen.
Thinking that it was something to do with my own code, I subclassed UIApplication so I could add a logging statement to -sendEvent:. When the laggy touch happens, -sendEvent: doesn't get called until some period of time after the touch has started, so it the touch handling code inside my UIView subclass doesn't appear to be at fault.
Does anyone have any idea what's going on here (other than iOS having some obscure bug)? Is there some sort of internal "events queue" that makes event delivery become laggy when it fills up? Has anyone else experienced this?
Touch events are only dispatched in the main UI run loop, and sometimes only when the main run loop goes idle for a bit. So if your app is busy handling several previous touch events in a row without taking a break, the main UI run loop might be saturated, and thus not get any further touch events until done with the current stuff.
Touch events also have time stamps. So you can check if they're coming too fast (faster than your event handlers and resulting UI updates can run), and skip or combine some of the event handlers, as appropriate for your app, if you want the app to stay maximally responsive.