Actors and components

This covers the basics of using AActor and UActorComponent

Enabling tick

The properties AActor.PrimaryActorTick / UActorComponent.PrimaryComponentTick are used to control the ticking functionality of actors and components. These properties are of type FTickFunction which is a struct (essentially a pointer to the C++ FTickFunction).

Enabling AActor tick:

public override void Initialize(FObjectInitializer initializer)
{
    base.Initialize(initializer);
    PrimaryActorTick.SetStartWithTickEnabled(true);
    PrimaryActorTick.SetCanEverTick(true);
}

Enabling UActorComponent tick:

public override void Initialize(FObjectInitializer initializer)
{
    base.Initialize(initializer);
    PrimaryComponentTick.SetStartWithTickEnabled(true);
    PrimaryComponentTick.SetCanEverTick(true);
}

It's best to enable tick in the Initialize function as the ticker is registered with the engine tickers just before the C# BeginPlay function is called. If you need to enable the ticker in BeginPlay you may need to manually register the ticker via FTickFunction.RegisterTickFunction.

Adding components to an AActor

This is an example of adding a UStaticMeshComponent as the RootComponent and then attaching a UTextRendererComponent.

[UClass]
class ATestActor : AActor
{
    [UProperty, EditAnywhere, BlueprintReadWrite]
    public UStaticMeshComponent Mesh { get; set; }

    [UProperty, EditAnywhere, BlueprintReadWrite]
    public UTextRenderComponent TextRenderer { get; set; }

    public override void Initialize(FObjectInitializer initializer)
    {
        UStaticMesh cubeMesh = ConstructorHelpers.FObjectFinder<UStaticMesh>.Find("StaticMesh'/Engine/BasicShapes/Cube.Cube'");
        if (cubeMesh != null)
        {
            Mesh = initializer.CreateDefaultSubobject<UStaticMeshComponent>(this, (FName)"Mesh");
            Mesh.SetStaticMesh(cubeMesh);
            RootComponent = Mesh;

            TextRenderer = initializer.CreateDefaultSubobject<UTextRenderComponent>(this, (FName)"TextRenderer");
            TextRenderer.SetupAttachment(Mesh);
            using (FText text = FText.FromString("Text component test"))
            {
                TextRenderer.SetText(text);
            }
        }
    }
}

Spawning an AActor and adding components at runtime

This is an example of spawning an AActor and adding a UStaticMeshComponent at runtime in the BeginPlay function of a AGameMode defined type.

[UClass]
class ATestGameMode : AGameMode
{
    protected override void BeginPlay()
    {
        base.BeginPlay();

        UStaticMesh cubeMesh = ConstructorHelpers.FObjectFinder<UStaticMesh>.Find("StaticMesh'/Engine/BasicShapes/Cube.Cube'");
        if (cubeMesh != null)
        {
            AActor actor = World.SpawnActor<AActor>(default(FVector), default(FRotator));
            UStaticMeshComponent meshComponent = NewObject<UStaticMeshComponent>(actor, (FName)"Mesh");
            meshComponent.SetStaticMesh(cubeMesh);
            meshComponent.RegisterComponent();
            actor.RootComponent = meshComponent;
        }
    }
}

Exposing components

By default components wont show up in the "Add Component" list in the editor. To enable this add the [BlueprintSpawnableComponent] attribute.

[UClass, BlueprintSpawnableComponent]
class UTestComponent : UActorComponent
{
}

Binding input

[UClass]
class AInputTestCharacter : ACharacter
{
    protected override void SetupPlayerInputComponent(UInputComponent playerInputComponent)
    {
        base.SetupPlayerInputComponent(playerInputComponent);

        // Set-up "Trigger" in the input bindings in the editor.
        playerInputComponent.BindAction("Trigger", EInputEventType.Pressed, OnTrigger);
    }

    // Must be marked as a [UFunction] so that the engine can call this function when the button is pressed
    [UFunction]
    private void OnTrigger()
    {
        PrintString("OnTrigger", FLinearColor.Red);
    }
}