I am working with a project with Slate UI and am currently using UE 4.27.2. After I made some classes in my original project, the game always crashed with access violation to address 0x80 after I tried to add a widget to the viewport. I figured out later that this was because that a class was directly inherited from SButton.
I made another project, a minimal example that would show this problem. First I created an empty C++ project. Then I added a Slate Widget class, as shown below:
SMyButton.h
#pragma once
#include "CoreMinimal.h"
#include "Widgets/SCompoundWidget.h"
/**
*
*/
class SBUTTONBUG_API SMyButton : public SButton
{
public:
SLATE_BEGIN_ARGS(SMyButton)
{}
SLATE_END_ARGS()
/** Constructs this widget with InArgs */
void Construct(const FArguments& InArgs);
};
SMyButton.cpp
#include "SMyButton.h"
#include "SlateOptMacros.h"
BEGIN_SLATE_FUNCTION_BUILD_OPTIMIZATION
void SMyButton::Construct(const FArguments& InArgs)
{
/*
ChildSlot
[
// Populate the widget
];
*/
}
END_SLATE_FUNCTION_BUILD_OPTIMIZATION
In this example, then I created a Level Script Actor to add this widget directly to the viewport at the beginning of the level. I overloaded its BeginPlay method to add the following code
void AMyLevelScriptActor::BeginPlay()
{
if (GEngine && GEngine->GameViewport)
{
GEngine->GameViewport->AddViewportWidgetContent(SAssignNew(button, SMyButton));
FSlateApplication::Get().SetKeyboardFocus(button, EFocusCause::SetDirectly);
}
}
, where button is defined as a private shared pointer to SMyButton in the header file
TSharedPtr<class SMyButton> button;
I also tried other methods to add the inherited button to the viewport, including,
- Add it to the viewport in BeginPlay() of the Game Mode
- Make the button a child of some other widgets (In my original project, I put it inside a slot of a VerticalBox, and put the VBox in another layer) and add this covering widget to the viewport
- Add some contents to the inherited button before adding it to the viewport
And all of them gave the same problem.
A screenshot at when the problem occurred is shown below
Here’s another screenshot at when the problem occurred in debug mode
I highly suspect this is a bug because it looked like a nullptr had been passed and was accessed (with some adjustment, probably a cast) because the address was always 0x80. Also, in debug mode, the code that caused the error could not be shown. It is not inside the SButton source code that I could see, but some compiled module of the engine.
But I am not very sure (maybe I should not inherit from SButton directly, but the documentation not says so), so I ask this question here.
