Accessing to second level object through pointers after OnClicked call causing CRASH

Development Programming & Scripting
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1

Hello,

I’m just moving my stuff from Unity to Unreal (5.1) and just observed something strange for me (maybe because of moving from c# to c++ and lack of knowledge).

I’ve created new plugin/module with window and created and put new widgets inside. I was trying to change relation structure between widgets but always get the same result which I attached below.

Final structure of module is like:

  • MainWindowModule
  • MainWidget (with some navigation buttons) [inside MainWindowModule]
    • ChildWidget (with some text editors , lists, etc) [inside MainWidget]

In MainWidget I keep pointer to the MainWindowModule

class SLATEQUICKSTARTWINDOW_API SQuickStartWindowMenu : public SCompoundWidget
{
private:
	FSlateQuickstartWindowModule* MainWindowModule;

public:
	SLATE_BEGIN_ARGS(SQuickStartWindowMenu)		
		{
		}
		SLATE_ARGUMENT(FSlateQuickstartWindowModule*, MainWindowModule)
	SLATE_END_ARGS()

	TSharedPtr<SAGFScenesManager> ScenesManagerWidget;

	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs);

	FReply OnFirstButtonClicked();
	FReply OnSecondButtonClicked();
	void LOGSOMETHING(); 
	FSlateQuickstartWindowModule* GetWindowModule();
}

and filling it with (in OnSpawnPluginTab method of FSlateQuickstartWindowModule)

SAssignNew(MainMenuWidget, SQuickStartWindowMenu).MainWindowModule(this)

In ChildWidget the code looks similar

class SLATEQUICKSTARTWINDOW_API SAGFScenesManager : public SCompoundWidget
{

private:
	SQuickStartWindowMenu* MainWindowMenuWidget;

public:
	SLATE_BEGIN_ARGS(SAGFScenesManager)
		{
		}
		SLATE_ARGUMENT(SQuickStartWindowMenu*, MainWindowMenuWidget)
	SLATE_END_ARGS()

	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs);

	FReply OnAddSceneButtonClicked();
	void LOGSOMETHING();
	SQuickStartWindowMenu* GetMenuWidget();
};

and filling it with (in Construct method of SQuickStartWindowMenu)

SAssignNew(ScenesManagerWidget, SAGFScenesManager).MainWindowMenuWidget(this)

As you can see each widget has it own LOGSOMETHING method (just sending something to log using UE_LOG). MainWindowModule also has it.

MainWidget and ChildWidget have their own buttons, and here is something which I don’t understand, I can just call only methods from used button widget and methods from the higher level widget.

when calling this on the lowest level in ChildWidget everything is OK

LOGSOMETHING();
MainWindowMenuWidget->LOGSOMETHING();

but calling this on the lowest level

MainWindowMenuWidget->GetWindowModule()->LOGSOMETHING();

crashing editor and throwing this:

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000000000000338

UnrealEditor_SlateQuickstartWindow_patch_0!SQuickStartWindowMenu::LOGSOMETHING() [D:\UnrealProjects\UnrealEdExtTest01\Plugins\SlateQuickstartWindow\Source\SlateQuickstartWindow\Private\AGFWidgets\SQuickStartWindowMenu.cpp:118]
UnrealEditor_SlateQuickstartWindow_patch_0!SAGFScenesManager::LOGSOMETHING() [D:\UnrealProjects\UnrealEdExtTest01\Plugins\SlateQuickstartWindow\Source\SlateQuickstartWindow\Private\AGFWidgets\Managers\SAGFScenesManager.cpp:102]
UnrealEditor_SlateQuickstartWindow_patch_0!SAGFScenesManager::OnAddSceneButtonClicked() [D:\UnrealProjects\UnrealEdExtTest01\Plugins\SlateQuickstartWindow\Source\SlateQuickstartWindow\Private\AGFWidgets\Managers\SAGFScenesManager.cpp:93]
UnrealEditor_SlateQuickstartWindow_patch_0!TBaseSPMethodDelegateInstance<0,SAGFScenesManager,1,FReply __cdecl(void),FDefaultDelegateUserPolicy>::Execute() [D:\Epic Games\UE_5.1\Engine\Source\Runtime\Core\Public\Delegates\DelegateInstancesImpl.h:295]

UnrealEditor_Slate ...

of course calling

MainWindowModule->LOGSOMETHING();

in the MainWidget works fine.

I’t looks like I cant get access to the second level pointer.

Any ideas? Thanks for any help with this!

2

Ok guys, I’ve found a solution.

Because of unknown to me reasons setting MainWindowModule and MainWindowMenuWidget pointers doesn’t work through Slate Arguments, I had to changed code from this

class SLATEQUICKSTARTWINDOW_API SQuickStartWindowMenu : public SCompoundWidget
{
private:
	FSlateQuickstartWindowModule* MainWindowModule;

public:
	SLATE_BEGIN_ARGS(SQuickStartWindowMenu)		
		{
		}
		SLATE_ARGUMENT(FSlateQuickstartWindowModule*, MainWindowModule)
	SLATE_END_ARGS()

	TSharedPtr<SAGFScenesManager> ScenesManagerWidget;

	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs);

	FReply OnFirstButtonClicked();
	FReply OnSecondButtonClicked();
	void LOGSOMETHING(); 
	FSlateQuickstartWindowModule* GetWindowModule();
}

to this

class SLATEQUICKSTARTWINDOW_API SQuickStartWindowMenu : public SCompoundWidget
{

private:
	FSlateQuickstartWindowModule* MainWindowModule = nullptr;

public:
	SLATE_BEGIN_ARGS(SQuickStartWindowMenu)		
		{
		}		
	SLATE_END_ARGS()

	TSharedPtr<SAGFScenesManager> ScenesManagerWidget;

	/** Constructs this widget with InArgs */
	void Construct(const FArguments& InArgs, FSlateQuickstartWindowModule* mainWindowModule);

	FReply OnScenesButtonClicked();
	FReply OnObjectsButtonClicked();
	void LOGSOMETHING(); 
	FSlateQuickstartWindowModule* GetWindowModule();
};

and changed filling pointer from

SAssignNew(MainMenuWidget, SQuickStartWindowMenu).MainWindowModule(this)

to

SAssignNew(MainMenuWidget, SQuickStartWindowMenu, this)

and after changing Construct method I added new line

void SQuickStartWindowMenu::Construct(const FArguments& InArgs, FSlateQuickstartWindowModule* mainWindowModule)
{   
    MainWindowModule = mainWindowModule;
    ...
}

I did the same things to the second widget and now all pointers are set properly in all widgets, and the crush effect disappeared