IOS touch event crashed

[warycat]

I suppose it could be a Xcode configuration error. I have no idea how to fix it.

I have a simple Metal View setup and running showing a simple texture. After I touch the screen it crashed.

Here is the event handling code. It works on my Mac, but crashes on my iPad.

fn handle_window_event(
    event: WindowEvent,
    control_flow: &mut ControlFlow,
    game_state: &mut GameState,
) {
    match event {
        WindowEvent::CloseRequested => *control_flow = ControlFlow::Exit,
        WindowEvent::MouseInput {
            device_id,
            state,
            button,
            modifiers,
        } => {
            if state == ElementState::Pressed {
                println!("Pressed");
                game_state.index += 1;
                game_state.index %= 60000;
            }
        }
        WindowEvent::Touch(touch) => match touch.phase {
            TouchPhase::Ended => {
                println!("Touched");
                game_state.index += 1;
                game_state.index %= 60000;
            }
            _ => {}
        },
        _ => {}
    }
}

Here is the error showing in console.

2021-11-07 16:21:47.507939-0800 TestWinit[5975:615681] MTLCommandQueue <CaptureMTLCommandQueue: 0x2803dd180> -> <MTLDebugCommandQueue: 0x2835b5980> -> <AGXA12FamilyCommandQueue: 0x13c8581d0>
    label = <none> 
    device = <AGXA12XDevice: 0x13800ea00>
        name = Apple A12X GPU
2021-11-07 16:21:52.087333-0800 TestWinit[5975:615681] *** Assertion failure in -[UIGestureGraphEdge initWithLabel:sourceNode:targetNode:directed:], UIGestureGraphEdge.m:24
2021-11-07 16:21:52.089250-0800 TestWinit[5975:615681] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid parameter not satisfying: sourceNode'
*** First throw call stack:
(0x1827ee04c 0x19ae62f54 0x1840a76cc 0x18524373c 0x184e963bc 0x18509bf98 0x184d5e618 0x184d928c8 0x184d9fa68 0x184f4f318 0x184d72c30 0x184d67a1c 0x184d6cec8 0x182810020 0x182820ce0 0x18275afe8 0x1827607f4 0x1827743b8 0x19e10438c 0x1851146a8 0x184e937f4 0x104f8dc04 0x104f8cc84 0x104f896a4 0x104f87b44 0x108c0da24)
libc++abi: terminating with uncaught exception of type NSException
dyld4 config: DYLD_LIBRARY_PATH=/usr/lib/system/introspection DYLD_INSERT_LIBRARIES=/Developer/usr/lib/libBacktraceRecording.dylib:/Developer/usr/lib/libMainThreadChecker.dylib:/usr/lib/libMTLCapture.dylib:/Developer/Library/PrivateFrameworks/DTDDISupport.framework/libViewDebuggerSupport.dylib
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid parameter not satisfying: sourceNode'
terminating with uncaught exception of type NSException

[maxammann]

I can confirm this bug on version 0.24 and 0.26. It also makes the app crash on my iPad. Right now I'm not handling touch events.

[maxammann]

I have a potential idea why this is happening based on this post: https://developer.apple.com/forums/thread/61432?answerId=204270022#204270022

Let's assume we initialize winit like this:

let mut event_loop = EventLoop::new();
let window = Window::new(&event_loop).unwrap();

event_loop.run(move |event, _, control_flow| {
...
});

1. First we create a new Window and initialize iOS views:

   winit/src/platform_impl/ios/window.rs

   Line 398 in 5eb9c95

   let view = view::create_view(&window_attributes, &platform_attributes, frame.clone());

2. Then we call run():

   winit/src/platform_impl/ios/event_loop.rs

   Line 102 in 1c4d6e7

   pub fn run<F>(self, event_handler: F) -> !

Based on the post from the apple forum, the initialization of the view is happening maybe too early. In fact it is happening before the UIApplication is created.
The views are created as soon as the main() function of the app is called. I suspect that this is too early.

[maxammann]

Could be related to:

• [iOS] Crashed by *** -[__NSArrayM insertObject:atIndex:]: object cannot be nil #1613
• Crash in iOS when swiping up for the control center #1705

[madsmtm]

Fixed by #3447 and #3826 (we first deprecated, and now disallow creating windows before the application has been initialized).