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The original tutorial is based on UE 4.18, I am based on UE 4.25.

English original Address

Follow up with a tutorial where an event is triggered when a character overlaps with a Trigger Box.

Create a new C++ TriggerBox subclass (which inherits from the TriggerBase class, which in turn inherits from the Actor class) and name it MyTriggerBox. Add the OnOverlapBegin and OnOverlapEnd functions to the header file.

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Here is the final.h header file (the original header code was wrong, fixed).

#pragma once

#include "CoreMinimal.h"
#include "Engine/TriggerBox.h"
#include "MyTriggerBox.generated.h"

/**
 *
 */
UCLASS()
class HELLOUNREAL_API AMyTriggerBox : public ATriggerBox {
    GENERATED_BODY()

  protected:

    // Called when the game starts or when spawned
    virtual void BeginPlay() override;

  public:

    // constructor sets default values for this actor's properties
    AMyTriggerBox();

    // declare overlap begin function
    UFUNCTION()
    void OnOverlapBegin(AActor* OverlappedActor, AActor* OtherActor);

    // declare overlap end function
    UFUNCTION()
    void OnOverlapEnd(AActor* OverlappedActor, AActor* OtherActor);
};
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In the.cpp file, to help us visualize the trigger box, we must use the #include drawdebughelpers.h file.

#include "MyTriggerBox.h"
// include draw debu helpers header file
#include "DrawDebugHelpers.h"
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We can also #define some debug log shortcuts.

#define print(text) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 1.5, FColor::Green,text)
#define printFString(text, fstring) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT(text), fstring))
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In the constructor of the actor, we shall send OnActorBeginOverlap. AddDynamic and OnActorEndOverlap AddDynamic registered overlapping events.

AMyTriggerBox::AMyTriggerBox()
{
    //Register Events
    OnActorBeginOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapBegin);
    OnActorEndOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapEnd);
}
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On BeginPlay, we will use the DrawDebugBox to draw the debug box.

void AMyTriggerBox::BeginPlay()
{
	Super::BeginPlay();

    DrawDebugBox(GetWorld(), GetActorLocation(), GetComponentsBoundingBox().GetExtent(), FColor::Purple, true, -1, 0, 5);
	
}
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Next, we’ll write an overlap function that prints a message to the screen indicating the actor that enters and exits the trigger box.

void AMyTriggerBox::OnOverlapBegin(class AActor* OverlappedActor, class AActor* OtherActor) { // check if Actors do not equal nullptr and that if (OtherActor && (OtherActor ! = this)) { // print to screen using above defined method when actor enters trigger box print("Overlap Begin"); printFString("Overlapped Actor = %s", *OverlappedActor->GetName()); } } void AMyTriggerBox::OnOverlapEnd(class AActor* OverlappedActor, class AActor* OtherActor) { if (OtherActor && (OtherActor ! = this)) { // print to screen using above defined method when actor leaves trigger box print("Overlap Ended"); printFString("%s has left the Trigger Box", *OtherActor->GetName()); }}Copy the code

Compile the code and drag and drop the new actor into the game as shown below

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The box that runs looks like this

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Here is the final.cpp file.

#define print(text) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 1.5, FColor::Green,text) #define printFString(text, fstring) if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT(text), fstring)) #include "MyTriggerBox.h" // include draw debu helpers header file #include "DrawDebugHelpers.h" AMyTriggerBox::AMyTriggerBox() { //Register Events OnActorBeginOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapBegin); OnActorEndOverlap.AddDynamic(this, &AMyTriggerBox::OnOverlapEnd); } // Called when the game starts or when spawned void AMyTriggerBox::BeginPlay() { Super::BeginPlay(); DrawDebugBox(GetWorld(), GetActorLocation(), GetComponentsBoundingBox().GetExtent(), FColor::Purple, true, -1, 0, 5); } void AMyTriggerBox::OnOverlapBegin(class AActor* OverlappedActor, class AActor* OtherActor) { // check if Actors do not equal nullptr and that if (OtherActor && (OtherActor ! = this)) { // print to screen using above defined method when actor enters trigger box print("Overlap Begin"); printFString("Overlapped Actor = %s", *OverlappedActor->GetName()); } } void AMyTriggerBox::OnOverlapEnd(class AActor* OverlappedActor, class AActor* OtherActor) { if (OtherActor && (OtherActor ! = this)) { // print to screen using above defined method when actor leaves trigger box print("Overlap Ended"); printFString("%s has left the Trigger Box", *OtherActor->GetName()); }}Copy the code

Finally, press the Play button to move the player in and out of the trigger box, resulting in the final image shown below.

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