变量、定时器和事件

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新建一个基于actor 的c++类

基于actorC++类新建一个蓝图，可在蓝图中调用父类方法

Countdown.h

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "Components/TextRenderComponent.h"
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "Countdown.generated.h"

UCLASS()
class HOWROUMG_API ACountdown : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	ACountdown();

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

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;

	//倒数的运行时长（以秒计）
	UPROPERTY(EditAnywhere)
	int32 CountdownTime;

	UTextRenderComponent* CountdownText;

	void UpdateTimerDisplay();

	void AdvanceTimer();
       //为了让非程序员调用C++函数，并用 **蓝图** 对其进行覆盖，需对 `Countdown.h` 进行以下修改
	UFUNCTION(BlueprintNativeEvent)
	void CountdownHasFinished();
	virtual void CountdownHasFinished_Implementation();

	FTimerHandle CountdownTimerHandle;

};

Countdown.cpp

// Fill out your copyright notice in the Description page of Project Settings.


#include "TimerManager.h"
#include "Countdown.h"

// Sets default values
ACountdown::ACountdown()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
    //将此Actor设为逐帧调用Tick()。如无需此功能，可关闭以提高性能。
    PrimaryActorTick.bCanEverTick = false;

    CountdownText = CreateDefaultSubobject<UTextRenderComponent>(TEXT("CountdownNumber"));
    CountdownText->SetHorizontalAlignment(EHTA_Center);
    CountdownText->SetWorldSize(150.0f);
    RootComponent = CountdownText;

    CountdownTime = 3;

}

// Called when the game starts or when spawned
void ACountdown::BeginPlay()
{
	Super::BeginPlay();
    //向新更新的函数添加调用，初始化 ACountdown::BeginPlay 中显示的文本，并设置逐秒前进和更新倒数的定时器：
    UpdateTimerDisplay();
    GetWorldTimerManager().SetTimer(CountdownTimerHandle, this, &ACountdown::AdvanceTimer, 1.0f, true);
	//note:由于在 ACountdown::BeginPlay 期间设置倒数，而非 ACountdown::ACountdown 期间，因此默认文本会在 关卡编辑器 中显示。
}

// Called every frame
void ACountdown::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}
//更新文本显示，以显示剩余时间。时间结束时，则显示为零。此代码应在游戏中首次生成 ACountdown 时运行，在 CountdownTime 变量为零前每秒运行一次。
void ACountdown::UpdateTimerDisplay()
{
   // CountdownText->SetText(FString::FromInt(FMath::Max(CountdownTime, 0)));
    CountdownText->SetText(FText::FromString(FString::FromInt(CountdownTime)));
}

void ACountdown::AdvanceTimer()
{
    --CountdownTime;
    UpdateTimerDisplay();
    if (CountdownTime < 1)
    {
        //倒数完成，停止运行定时器。
        GetWorldTimerManager().ClearTimer(CountdownTimerHandle);
        //定时器结束时，执行要执行的特殊操作。
        CountdownHasFinished();
    }
}

void ACountdown::CountdownHasFinished_Implementation()
{
    //改为特殊读出
   CountdownText->SetText(FText::FromString("GO!"));

}