.Net MAUI Drag & Drop crashes on Mac Catalyst with Apple Silicon

Question

Overview

On Macs with Apple Silicon processors, Drag & Drop seems to be broken for .Net MAUI apps. I have tried multiple fixes/workarounds, but so far I haven't been successful. Do you have a better suggestion?

The Details

I have built a moderately complex B2B app in .Net Maui 8. One of it's core features uses "drag and drop" functionality to copy images from a list to a 2D layout. We recently adjusted our scope to include MacOS support. (Originally, we only targeted iPad and Windows). When running the app on Mac Catalyst, I get the following behavior:

When dragging begins, an error message is displayed in debug output:

2024-07-16 06:31:15.674 MacCatalystDragDropTest[1058:13565] Cannot find representation conforming to type com.apple.uikit.private.drag-item

However, the draggable view appears to begin the drag operation normally. A copy of the view follows the mouse pointer around the screen. When I drop the image on the target, this error appears in the debug output:

2024-07-16 06:31:16.294 MacCatalystDragDropTest[1058:13565] *** Assertion failure in -[NSFilePromiseReceiver receivePromisedFilesAtDestination:options:operationQueue:reader:], NSFilePromiseReceiver.m:349

None of the events or commands configured on the DropGestureRecognizer of the target run. After the error, the source element cannot be dragged again until the app is re-launched.

A Minimal Reproducible Example

I have created a test app to demonstrate that the issue was not caused by any code in my main app. You can find the test app here. It is a standard .Net Maui app. The only change I made was adding the following elements to MainPage.xaml:

<Image Source="dotnet_bot.png">

    <Image.GestureRecognizers>

        <DragGestureRecognizer/>

    </Image.GestureRecognizers>

</Image>

<Image Source="dotnet_bot.png">

    <Image.GestureRecognizers>

        <DropGestureRecognizer/>

    </Image.GestureRecognizers>

</Image>

When running this very simple app, I receive identical behavior to the original app. Important note: this issue has not yet been confirmed on Macs with Intel processors. To my knowledge, both devices where the behavior was observed had an Apple M2 processor.

Environment Details

• Computer: Mac Mini with an Apple M2 processor
• Operating system: MacOS Sonoma 14.5 (also tested on 14.1.1)
• Mac Dev Software: Xcode 15.4
• .Net version: .Net SDK 8.0.303 (also observed in an earlier version)
• Workloads: .Net MAUI workload 8.0.61/8.0.100
• Nugets: .Net MAUI version 8.0.70 (also observed with 8.0.61 and another earlier version)

Troubleshooting Steps Already Completed

• I have created a clean app to test (see above)
• I have completely uninstalled .Net & Mono from my Mac and reinstalled them (The behavior didn't change)
• I attempted to bypass GestureRecognizers and add UI interaction code directly to the underlying native views following this and this example code. (I received the same error messages even with custom code)
• I reported the problem to Microsoft. (They confirmed the behavior but haven't issued any guidance).

The next steps

I need a way forward! Can you help? Is there an alternate method to working with the native views? Something I'm missing with the GestureRegonizers?

Answer 1

This bug was caused by operating the Mac via Remote Management. In my case, I used RealVNC Viewer from my Windows computer. (My desk is too small for two separate workstations, so I normally don't have a keyboard, mouse, or monitor connected directly to my Mac). When operating the app via directly-connected hardware, it functions as expected. Although it would be interesting to find the cause of the bug in remote management, I am marking this question as answered since the app is functional under normal operation. (Remote Management support is not a requirement in production)