Our project has recently seen a crash with SComboBox using UE 4.14.0. The dropdown menu will flicker constantly when first opened and attempting to click on it can cause a crash.
I’ve been able to repro this in the Slate Viewer app created from the GitHub 4.15.1-release using the following steps:
Open the Slate Viewer application.
Select the Widget Gallery tab.
Position the main window such that the dropdown menu will go beyond the bottom of the screen.
Open the “Item A N” dropdown menu.
Attempt to click on “Item A 1 or 2” in the dropdown making sure that the mouse click is above the Combo Button widget.
When the menu opens on top of another ComboButton/Box, the click goes through to the underlying ComboButton/Box and causes the check in SMenuAnchor::SetIsOpen line 379 to fire. This only seems to happen when the newly opened dropdown menu is flickering above and below the original box. If it does not crash, the process must be started over completely as subsequent clicks on the “Item A N” combobox will cause the dropdown to open above the original menu.
The repro steps listed above were for the Slate Viewer application built from a clean pull of the 4.15.1-release tag in GitHub.
A project is not required as this can be reproduced outside of the normal UE4 Editor and prior to adding a project.
Similar to 2 as the error we receive in our project is the same that occurs in the unmodified Slate Viewer application.
These are the steps I followed to repro the issue in a clean version of 4.15.1-release:
Pull 4.15.1-release from GitHub.
Run Setup.bat and GenerateProjectFiles.bat.
Build Engine->UE4 in Development Editor.
Build Programs->SlateViewer in Development Editor.
Launch the Slate Viewer application from either VisualStudio or the Binaries directory.
Select the Widget Gallery tab.
Position the main window such that the dropdown menu will go beyond the bottom of the screen (shown in the “Menu Position” image above).
Select the “Item A N” dropdown menu.
Attempt to click on “Item A 1" or "Item A 2” in the dropdown making sure that the mouse click is above the Combo Button widget (shown in the “Click Area” image above).
Please let me know if I can provide any additional information.
After further testing I was able to reproduce this issue on our end. I have provided a link to the public tracker. Please feel free to use the link provided for future updates.
We are still running into this issue in the latest release of 4.19.0. The repro steps listed above are accurate but the public tracker has been closed as “Cannot Reproduce”. I’ve attached a short video to illustrate how this bug happens.
In our project, we have a several dropdowns that will extend below the bottom of the screen due to the position of the window. While the crash is a problem, the more annoying issue is that every combo box must be clicked on three times before it is usable. Once the menu opens up correctly after the third click, the combo box behaves as expected.
If anyone has any advice on ways to fix the flickering issue I’d appreciate it.
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