在UE4使用计时器实现一个倒计时事件

.h文件定义

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

UCLASS()
class CLASSSIMPES_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;

    UPROPERTY(EditAnywhere)
    int32 CountdownTime;
    UTextRenderComponent* CountdownText;

    void UpdateTimerDisplay();//更新显示
    void AdvanceTimer();
    void CountdownHasFinished();//时间结束时的特殊动作

    FTimerHandle CountdownTimerHandle;//句柄
};

类定义详解

int32 CountdownTime//定义了一个int32类型的倒计时时间

int32为虚幻整数类型，虚幻整数类型分为有符号和无符号，分别为int和unit，有8,16,32,64四种。

UTextRenderComponent* CountdownText//定义了一个UTextRenderComponent类的可显示文本组件

在头文件中只是先声明，在cpp里还要用CreateDefaultSuobject创建完整的组件

void UpdateTimerDisplay()//创建了一个更新器，用于更新显示字体

void AdvanceTimer()//

void CountdownHasFinished()//用于结束时执行的特殊动作

FTimerHandle CountdownTimerHandle//定义了一个句柄

句柄：用于识别的唯一ID

.cpp文件

#include "Countdown.h"

// Sets default values
ACountdown::ACountdown()//类当中的参数初始化
{
     // Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
    PrimaryActorTick.bCanEverTick = false;
    //将此Actor设为逐帧调用Tick(),关闭提高性能

    CountdownText = CreateDefaultSubobject<UTextRenderComponent>(TEXT("CountdownNumber"));//添加TEXTRENDER组件
    CountdownText->SetHorizontalAlignment(EHTA_Center);//设置对齐方式
    CountdownText->SetWorldSize(150.0f);//设置大小
    RootComponent = CountdownText;//设置这个组件为根组件
    CountdownTime = 3;//初始化倒计时





}

// Called when the game starts or when spawned
void ACountdown::BeginPlay()//开始时执行
{
    Super::BeginPlay();

    UpdateTimerDisplay();//
    GetWorldTimerManager().SetTimer(CountdownTimerHandle, this, &ACountdown::AdvanceTimer, 1.0f, true);    
}

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

}

void ACountdown::UpdateTimerDisplay()
{
    CountdownText->SetText(FString::FromInt(FMath::Max(CountdownTime, 0)));
    //Max:比较两数较大者，并返回较大数
    //FromInt:强制类型转换，将int类型强制转化为string类型
    //settext:设置字体组件里的值
}

void ACountdown::AdvanceTimer()
{
    --CountdownTime;//减去倒数时间1

    UpdateTimerDisplay();//更新显示

    if (CountdownTime < 1)
    {
        //倒数完成，停止运行定时器
        GetWorldTimerManager().ClearTimer(CountdownTimerHandle);
        CountdownHasFinished();
    }
}

void ACountdown::CountdownHasFinished()
{
    //改为特殊读出
    CountdownText->SetText(TEXT("GO"));
}

.cpp文件详解

Countdown()构造函数

CreateDefaultSubobject初始化
SetHorizontalAlignment(EHTA_Center);设置对齐方式:对齐方式还有EHTA_Left,EHTA_Right.
SetWorldSize(150.0f);设置大小,接受一个浮点值
CountTime初始化倒计时时间

UpdateTimerDisplay()

SetText(FString::FromInt(FMath::Max(CountdownTime, 0)))

//Max:比较两数较大者，并返回较大数

//FromInt:强制类型转换，将int类型强制转化为string类型

//settext:设置字体组件里的值

AdvanceTimer()//计时器,实行倒计时事件

定时器函数(Timer)

template<class UserClass> void SetTimer ( FTimerHandle & InOutHandle, UserClass * InObj, typename FTimerDelegate::TUObjectMethodDelegate< UserClass >::FMethodPtr InTimerMethod, float InRate, bool InbLoop, float InFirstDelay )