Setting up a Button to start a Drag and Drop Operation

[DavidCR (David_CR97)]

Hello,
I was trying to set up a button to start a Drag and Drop operation, instead of the classic MouseButtonDown.

This is the idea that I was trying to replicate.

At the moment, my slot has a MenuAnchor to display those buttons.

And when I click on the slot, the menu will open. After that, when I click on the Move button, it will “say to the slot” that it must start a DragDrop Operation, and the menu will be closed.

My problem here is to start the DragDrop Operation. I already tried different approaches without luck. I think that maybe I’m creating a new operation, but it’s not being returned to nowhere, something that happens on “NativeOnDragDetected”.

NativeOnDragDetected(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent,
	UDragDropOperation*& OutOperation)

Below, there is my latest attempt:

I inherit my class from UUserWidget and TSharedFromThis<SObjectWidget>.

After the click on the button, it will say to the slot to run this function:
.cpp

void USlotLayout::BeginDragDrop(ULocalPlayer* LocalPlayer, UDragDropOperation* Operation, int32 PointerIndex) {
	if (LocalPlayer /* && Operation*/ )
	{
		TSharedPtr<const FSlateUser> SlateUser = LocalPlayer->GetSlateUser();
		FVector2D ScreenCursorPos = SlateUser->GetCursorPosition();
		
		FVector2D ScreenDraggedPosition = SlateUser->GetCursorPosition(); 

		const float DPIScale = UWidgetLayoutLibrary::GetViewportScale(LocalPlayer);

		TSharedRef<FUMGDragDropOp> DragDropOp = 
			FUMGDragDropOp::New(Operation, PointerIndex, ScreenCursorPos, ScreenDraggedPosition, DPIScale, SharedThis(this));

		LocalPlayer->GetSlateOperations().BeginDragDrop(DragDropOp);
	}
}

And getting an error on ShareThis(this)

If you have any idea about what’s going on, or if you have another way to do it, I appreciate your help. I’m not sure if I gave enough information, but if you need something more to help me to fix this, just say it.
Thanks!

[MittzyZea]

Hi David, sorry to necro but did you ever figure this out?

[DavidCR (David_CR97)]

Hello MittzyZea.
Unfortunately, I stopped the work that I was doing in this project, and never found a solution for this.

I can try to fix it and return with a solution, but I don’t promise anything.

Have you tried using CommonUI?

[DavidCR (David_CR97)]

I solved this out by using OnMouseButtonDown() to create a DragDropOperation (it was needed a function that returns a FReply).

Nowadays, it must be a cleaner solution.
Let’s not forget that this project is 2+ years old, and it’s kinda outdated.

[MittzyZea]

Hi, Thanks for the response! I didn’t see it for a few days, sorry.

I ended up solving this issue myself by creating a custom button class that supports drag and drop, like you did. Here’s the code for anyone who may find it useful:

(Note: This will not work if you just copy paste it in to your project. It depends on CommonUI and a custom library of mine, but is easily adaptable! Also remember, I’m a noob. There’s probably some bad stuff in here.)

Header File

#pragma once

#include "CoreMinimal.h"
#include "InputCoreTypes.h"
#include "UI/STUserWidget.h"
#include "STUWButton.generated.h"

// ButtonEvent and CursorEvent are similar, but CursorEvent passes the mouses position.
DECLARE_MULTICAST_DELEGATE(FST_ButtonEvent);
DECLARE_MULTICAST_DELEGATE_OneParam(FST_CursorEvent, FVector2D); // FVector2D = Mouse Position


/**
 * A button which supports clicking and dragging.
 */
UCLASS()
class MYPROJECT_API USTUWButton : public USTUserWidget
{
  GENERATED_BODY()

protected:

  virtual void NativePreConstruct() override;

  virtual FReply NativeOnMouseButtonDown(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent) override;
  virtual FReply NativeOnMouseButtonUp(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent) override;
  virtual void NativeOnMouseEnter(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent) override;
  virtual void NativeOnMouseLeave(const FPointerEvent& InMouseEvent) override;
  virtual FReply NativeOnMouseMove(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent) override;
  virtual void NativeOnDragDetected(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent, UDragDropOperation*& OutOperation) override;

public:

  UPROPERTY(meta = (BindWidget)) TObjectPtr<class UCommonBorder> MainButtonBody;
  UPROPERTY(EditAnywhere, meta = (BindWidgetOptional)) TObjectPtr<class UCommonRichTextBlock> MainButtonLabel;
  UPROPERTY(EditAnywhere, meta = (BindWidgetOptional)) TObjectPtr<class UCommonLazyImage> MainButtonImage;
  UPROPERTY(EditAnywhere, meta = (BindWidgetOptional)) TObjectPtr<class UCommonRichTextBlock> SecondaryButtonLabel;
  
  UPROPERTY() TObjectPtr<USTUserWidget> OwningWidget; // The widget that this button is on. Not necessary to set, but you can use this to use GetNewDragDropOperation() on the parent instead of subclassing the button. 

  UPROPERTY() bool bIsPrimaryPressed;
  UPROPERTY() bool bIsSecondaryPressed;
  
  FST_ButtonEvent OnButtonPressedPrimary; // Usually called on Left Mouse Button. This is NOT a click event.
  FST_CursorEvent OnButtonGrabbed; // The same as OnButtonPressedPrimary, but allows you to pass the cursors location.
  FST_ButtonEvent OnButtonPressedSecondary; // Usually called on Right Mouse Button. This is NOT a click event.
  FST_ButtonEvent OnButtonReleased; 
  FST_ButtonEvent OnButtonClickedPrimary; // Usually called on Left Click.
  FST_ButtonEvent OnButtonClickedSecondary; // Usually called on Right Click.
  FST_ButtonEvent OnButtonHovered;
  FST_ButtonEvent OnButtonUnhovered;
  FST_CursorEvent OnButtonDragDetected;
  FST_CursorEvent OnButtonMouseMove;
  
  UPROPERTY(EditAnywhere, BlueprintReadOnly, Category = Style, meta = (ExposeOnSpawn = true))
  TSubclassOf<class UCommonButtonStyle> Style; // The buttons style asset // TODO: Make custom UCommonButtonStyle equivalent.
  
  UPROPERTY(EditAnywhere, DisplayName = "Enabled") bool bIsButtonEnabled = true; // Is this button active?
  UPROPERTY(EditAnywhere, DisplayName = "Draggable") bool bIsButtonDraggable = false; // Should this button look for drag-drop events?

  // Not sure how good of an idea this is
  UPROPERTY(EditAnywhere, DisplayName = "Primary Input") FKey PrimaryInputButton = EKeys::LeftMouseButton; // The input that activates the buttons primary function
  UPROPERTY(EditAnywhere, DisplayName = "Secondary Input") FKey SecondaryInputButton = EKeys::RightMouseButton; // The input that activates the buttons secondary function
  
};

C++ File

#include "UI/General/Button/STUWButton.h"

#include "CommonBorder.h"
#include "CommonButtonBase.h"
#include "UI/STUserInterfaceStatics.h"
#include "Blueprint/WidgetBlueprintLibrary.h"
#include "Kismet/KismetInputLibrary.h"

void USTUWButton::NativePreConstruct()
{
  if(MainButtonBody)
  {
    MainButtonBody->SetBrush(Style.GetDefaultObject()->NormalBase);
  }
}

FReply USTUWButton::NativeOnMouseButtonDown(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent)
{
  GEngine->AddOnScreenDebugMessage(-1, 2, FColor::Red, "Mouse Down Detected");
  if(bIsButtonEnabled)
  {
    if(InMouseEvent.GetEffectingButton() == PrimaryInputButton)
    {
      bIsPrimaryPressed = true;
      OnButtonPressedPrimary.Broadcast();
      OnButtonGrabbed.Broadcast(USTUserInterfaceStatics::ScreenSpacePosToViewportSpacePos(this, UKismetInputLibrary::PointerEvent_GetScreenSpacePosition(InMouseEvent)));
      if(bIsButtonDraggable)
      {
        FEventReply EventReply = UWidgetBlueprintLibrary::DetectDragIfPressed(InMouseEvent, this, PrimaryInputButton);
        return UWidgetBlueprintLibrary::CaptureMouse(EventReply, this).NativeReply;
      }
      else{return FReply::Handled();}
    }

    else if(InMouseEvent.GetEffectingButton() == SecondaryInputButton)
    {
      bIsSecondaryPressed = true;
      OnButtonPressedSecondary.Broadcast();
      return FReply::Handled();
    }
  }
  return FReply::Unhandled();

}

FReply USTUWButton::NativeOnMouseButtonUp(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent)
{
  GEngine->AddOnScreenDebugMessage(-1, 2, FColor::Red, "Mouse Up Detected");
  OnButtonReleased.Broadcast();
  OnButtonClickedPrimary.Broadcast(); // NOTE: This is a BAD way of detecting clicks. Ive just not learned the proper way myself yet. I do NOT recommend detecting clicks like this!

  if(InMouseEvent.GetEffectingButton() == PrimaryInputButton)
  {
    bIsPrimaryPressed = false;
    if(HasMouseCapture())
    {
      FEventReply EventReply = FEventReply(true);
      return UWidgetBlueprintLibrary::ReleaseMouseCapture(EventReply).NativeReply;
    }
  }
  if(InMouseEvent.GetEffectingButton() == SecondaryInputButton)
  {
    bIsSecondaryPressed = false;
  }
  return FReply::Handled();
}

void USTUWButton::NativeOnMouseEnter(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent)
{
  
}
void USTUWButton::NativeOnMouseLeave(const FPointerEvent& InMouseEvent)
{
  
}

FReply USTUWButton::NativeOnMouseMove(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent)
{
  Super::NativeOnMouseMove(InGeometry, InMouseEvent);
  OnButtonMouseMove.Broadcast(USTUserInterfaceStatics::ScreenSpacePosToViewportSpacePos(this, UKismetInputLibrary::PointerEvent_GetScreenSpacePosition(InMouseEvent)));
  return FReply::Handled();
}


void USTUWButton::NativeOnDragDetected(const FGeometry& InGeometry, const FPointerEvent& InMouseEvent, UDragDropOperation*& OutOperation)
{
  GEngine->AddOnScreenDebugMessage(-1, 2, FColor::Red, "Drag Detected");
  Super::NativeOnDragDetected(InGeometry, InMouseEvent, OutOperation);
  OnButtonDragDetected.Broadcast(USTUserInterfaceStatics::ScreenSpacePosToViewportSpacePos(this, UKismetInputLibrary::PointerEvent_GetScreenSpacePosition(InMouseEvent)));
  
  if(OwningWidget)
  {
    OutOperation = OwningWidget->GetNewDragDropOperation();
  }
}