Screen edge pan gesture is not recognized

[Fitzmaz]

Description

I am encountering difficulty in activating the built-in interactivePopGestureRecognizer. I have attempted to simulate a screen edge pan gesture using the dragFromPoint:displacement:steps: method, but the gesture is not being recognized.

Code Snippet

CGFloat majorSwipeDisplacement = UIScreen.mainScreen.bounds.size.width * 0.5;
CGFloat minorSwipeDisplacement = 5;
KIFDisplacement displacement = CGPointMake(majorSwipeDisplacement, minorSwipeDisplacement);

[view dragFromPoint:CGPointMake(0.5, 150) displacement:displacement steps:20];

Environment

• iOS version: 14.7, 16.1
• Xcode version: 14.1

[Fitzmaz]

As mentioned in Pull Request #776, interactivePopGestureRecognizer was able to be triggered successfully. Looks like something might have changed in the iOS SDK.

[dostrander]

@Fitzmaz I'd possibly try more steps and possibly start at 10-20 for x and middle of the screen for y. The maybe jump the steps to 100?

I don't have time currently to investigate this right now but if you can't repro or fix I'll try to get to it ASAP!

\cc @steve-sun-me

[Fitzmaz]

@dostrander Thanks for the advices. I've experimented with various parameters, but none of them seem to work. So I don't think it's a problem with the parameters themselves.

Then, I did some digging and compared the UITouch object of a normal pan gesture with that of a screen edge pan gesture. It turns out that the touch object of the screen edge pan gesture has a property called _edgeType that is set, while the touch object of the normal pan gesture does not have this property set.

Regarding the KIF framework, touch objects are generated within the dragPointsAlongPaths: method. I discovered that if I manually set the _edgeType property of the touch object to a value of 4, the screen edge pan gesture is recognized successfully. Maybe we should add a new method to the tester that can simulate a screen edge pan gesture and automatically set the touch object's property to the right value?

[dostrander]

@Fitzmaz that seems like a decent solution to me.

One thing i find a little strange is why the edge pan gesture doesn't pick up the drag as it would normally? I'm curious how it would normally set that edge type under the hood

[Fitzmaz]

@dostrander The _edgeType property was introduced on iOS 7 along with the UIScreenEdgePanGestureRecognizer class. Unfortunately, I don't have an old device to test the behavior on iOS 7. I have only tested on some devices and obtained the following results:

	_edgeType == 0	_edgeType == 1	_edgeType == 2	_edgeType == 4
iPhone 6, 11.3.1	❌	✅(default for edge pan)	✅	✅
iPhone SE2, 15.0	❌	✅(default for edge pan)	❌	✅
iPhone X, 14.7	❌	✅	❌	✅(default for edge pan)
iPhone 13, 15.6	❌	✅	❌	✅(default for edge pan)
iPhone 14, 16.1	❌	✅	❌	✅(default for edge pan)

Based on these results, I can draw a few conclusions:

1. It seems that the edge pan gesture no longer picks up the drag since iOS 11, and possibly even earlier versions.
2. Setting the _edgeType property to either value 1 or value 4 makes the touch recognized.
3. The default value for an edge pan on iPhone models with a notch is 4, while on models with a home button it's 1.

[dostrander]

Thanks for the info. I'm still wondering if there is a way to have iOS detect the edge pan without having to set a variable on some underlying object. I would expect the way you drag that they'd detect it 🤔

[justinseanmartin]

I think Apple does for real gestures, but I'd guess at a lower level than how KIF synthesizes UITouch events.

[Fitzmaz]

@dostrander Normally, the _edgeType property is set inside the _UITouchSetBasicTouchPropertiesFromEvent function.

* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 22.1
  * frame #0: 0x000000010e2332c4 UIKitCore`-[UITouch _setEdgeType:]
    frame #1: 0x000000010e23378c UIKitCore`_UITouchSetBasicTouchPropertiesFromEvent + 944
    frame #2: 0x000000010e23dea0 UIKitCore`____updateTouchesWithDigitizerEventAndDetermineIfShouldSend_block_invoke.27 + 1576
    frame #3: 0x000000010e24f0f4 UIKitCore`_UIEventHIDEnumerateChildren + 160
    frame #4: 0x000000010e241920 UIKitCore`__dispatchPreprocessedEventFromEventQueue + 2232
    frame #5: 0x000000010e244774 UIKitCore`__processEventQueue + 5612

As @justinseanmartin mentioned, KIF synthesizes UITouch and the underlying IOHIDEvent, which means that the _UITouchSetBasicTouchPropertiesFromEvent function won't be called at all.