目录
前言
步骤
一、 搭建异步蓝图节点框架
二、异步蓝图节点嵌入到引擎的执行流程
三、获取本地时间并异步返回
四、获取网络时间并异步返回
五、源码
前言
本文以请求网络/本地时间API为例，介绍如何实现HTTP异步请求。
步骤
一、 搭建异步蓝图节点框架
1. 在“xxx.Build.cs”中添加“HTTP”模块
2. 新建一个空白C++类
添加反射
按UE规范命名
让创建的C++类继承自 UBlueprintAsyncActionBase 类
添加元数据标签，替代默认执行引脚
定义一个枚举类型 ESampleNetTimeType，包含TaoBao 和 Local枚举值，分别代表淘宝时间和本地时间。
定义一个蓝图可调用的静态函数 SampleHttpTimeAsyncAction，该静态函数接受一个 UObject* 类型的世界上下文对象和一个 ESampleNetTimeType 枚举类型的参数，返回值是一个指向 USampleHttpTime 类对象的指针。
编译后可以看到此时蓝图节点 SampleHttpTimeAsyncAction，如下所示，该节点已经隐藏了默认的Then执行引脚
在添加自定义输出引脚之前，需要先申明一个动态多播。其中bResult表示请求是否成功；Message用于传递错误信息或者成功提示；RespInfo是一个结构体，用于传递网络时间响应的详细信息。
定义三个可在蓝图中赋值的动态多播委托：Then、OnSuccess 和 OnFail，分别用于在操作执行后、操作成功和操作失败时触发
此时运行可以看到蓝图节点 SampleHttpTimeAsyncAction，如下所示：
二、异步蓝图节点嵌入到引擎的执行流程
1. 定义成员变量：AsyncID 用于唯一标识异步操作，NetTimeType 用于存储网络时间类型，默认值为 ESampleNetTimeType::Local
构造函数传入初始化对象所需的各种信息
通过 Super(ObjectInitializer)，将接收到的 FObjectInitializer 参数传递给基类的构造函数，以确保基类也能正确初始化
继续实现 SampleHttpTimeAsyncAction 静态函数，该函数创建一个 USampleHttpTime 对象，并设置其网络时间类型。RegisterWithGameInstance 函数用于将该异步操作对象注册到游戏实例中，确保其生命周期与游戏实例同步
在创建USampleHttpTime 对象后，“UBlueprintAsyncActionBase”类的“Activate”方法将被调用。接下来重写“UBlueprintAsyncActionBase”类的“Activate”方法
先调用父类的激活逻辑，然后在游戏线程上异步执行 Activate_Internal 方法，最后广播一个事件通知异步任务已经启动，需要等待完成。
此时运行如下：
此时当异步任务执行完毕后，我们希望“SampleHttpTimeAsyncAction”的“On Success”/“On Fail”引脚执行输出，需要继续在“Activate_Internal”函数中补充异步任务内容。
三、获取本地时间并异步返回
补充函数“Activate_Internal”实现如下，依据 NetTimeType 的值来确定是从网络获取时间，还是使用本地时间。若从网络获取时间，会设置相应的网络时间服务器 URL；若使用本地时间，则获取当前本地时间和 UTC 时间赋值给结构体“RespInfo”，并调用成功回调函数“CallOnSuccess”将“RespInfo”传递出去，最后释放资源。
函数“CallOnSuccess”、“CallOnFaild”、“RealeaseResources”定义和实现如下。其中：
“CallOnSuccess”函数的作用是在操作成功时，将成功的相关信息（异步任务 ID、结果状态、消息和时间响应信息）广播给所有绑定到 OnSuccess 委托的函数。
“CallOnFaild”函数的作用是在操作失败时，将失败的相关信息（异步任务 ID、结果状态、消息和时间响应信息）广播给所有绑定到 OnFail 委托的函数。
“RealeaseResources”函数的作用是释放 USampleHttpTime 对象占用的资源，具体包括清除委托绑定和标记对象为可销毁状态。其中， Clear 方法会移除所有绑定到 Then 委托的函数，释放委托占用的资源； SetReadyToDestroy 方法，将 USampleHttpTime 对象标记为可销毁状态，引擎会在合适的时候销毁该对象，释放占用的内存和其他资源。
结构体“RespInfo”定义如下
选择本地时间
打印返回的北京时间和UTC时间
此时打印结果如下，可以看到成功打印时间信息
四、获取网络时间并异步返回
获取网络时间的api接口地址：https://acs.m.taobao.com/gw/mtop.common.getTimestamp/
响应信息如下：
{"api": "mtop.common.getTimestamp","v": "*","ret": ["SUCCESS::接口调用成功"],"data": {"t": "1744101991020"}
}导入所需头文件
实现发送HTTP请求的函数如下，需要设置请求的 URL、请求方法、请求头和请求体内容，当 HTTP 请求完成后执行回调函数“OnHttpRespReceived”。
定义返回时间信息的结构体
定义嵌套的结构体
实现接收HTTP响应的函数“OnHttpRespReceived”如下，如果请求和响应成功，就会解析响应中的 JSON 数据，提取时间戳并转换为 UTC 时间和北京时间，然后通过函数“CallOnSuccess”通知请求成功。
在蓝图中改使用网络api接口
此时运行就可以获取到网络返回的时间了
五、源码
SampleHttpTime.h
// Fill out your copyright notice in the Description page of Project Settings.#pragma once#include "CoreMinimal.h"#include "Interfaces/IHttpRequest.h"
#include "HttpModule.h"
#include "Interfaces/IHttpResponse.h"#include "Kismet/BlueprintAsyncActionBase.h"#include "SampleHttpTime.generated.h"UENUM(BlueprintType)
enum class ESampleNetTimeType :uint8
{TaoBao UMETA(DisplayName = "TaobaoTimeAPI"),Local UMETA(DisplayName = "LocalTimeAPI"),MaxNum UMETA(Hidden)
};USTRUCT(BlueprintType)
struct STUDY_API FNetTimeRespDataInfo
{GENERATED_BODY()
public:UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FString t = TEXT("");
};USTRUCT(BlueprintType)
struct STUDY_API FSampleNetTimeRespMessage
{GENERATED_BODY()
public:UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FString api = TEXT("");UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FString v = TEXT("");UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")TArray<FString> ret;UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FNetTimeRespDataInfo data;
};USTRUCT(BlueprintType)
struct STUDY_API FSampleNetTimeRespInfo
{GENERATED_BODY()
public:UPROPERTY(EditAnywhere, BlueprintReadWrite, Category="NetTime")FDateTime BeijingDateTime = FDateTime();UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FDateTime UTCDateTime = FDateTime();UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FSampleNetTimeRespMessage RespMessage;UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "NetTime")FString RawMessage = TEXT("");
};DECLARE_DYNAMIC_MULTICAST_DELEGATE_FourParams(FSampleNetTimeDelegate, FGuid, AsyncID, bool, bResult, FString, Message, FSampleNetTimeRespInfo, RespInfo
);UCLASS(meta = (HideThen = true)) //隐藏默认的then引脚
class STUDY_API USampleHttpTime : public UBlueprintAsyncActionBase
{GENERATED_BODY()public:USampleHttpTime(const FObjectInitializer& ObjectInitializer = FObjectInitializer::Get());virtual ~USampleHttpTime();UFUNCTION(BlueprintCallable, meta = (BlueprintInternalUseOnly = "true", //表明该函数主要用于蓝图内部使用，通常不希望在蓝图库中直接显示。WorldContext = "WorldContextObject", DisplayName = "SampleHttpTimeAsyncAction", //指定函数在蓝图中的显示名称Keywords = "Sample Net Time" //为函数添加搜索关键词，方便在蓝图中搜索该函数), Category = "Sample|NetTime")static USampleHttpTime* SampleHttpTimeAsyncAction(UObject* WorldContextObject, ESampleNetTimeType InNetTimeType);public:virtual void Activate() override;virtual void Activate_Internal();public:UPROPERTY(BlueprintAssignable)FSampleNetTimeDelegate Then;UPROPERTY(BlueprintAssignable)FSampleNetTimeDelegate OnSuccess;UPROPERTY(BlueprintAssignable)FSampleNetTimeDelegate OnFail;protected:void SendHttp(const FString& InServerURL);void OnHttpRespReceived(FHttpRequestPtr HttpRequest, FHttpResponsePtr HttpResponse, bool bSucceeded);void CallOnSuccess(FGuid InAsyncID, bool bInResult, FString InMessage, FSampleNetTimeRespInfo RespInfo);void CallOnFaild(FGuid InAsyncID, bool bInResult, FString InMessage, FSampleNetTimeRespInfo RespInfo);void RealeaseResources();protected:FGuid AsyncID = FGuid::NewGuid();ESampleNetTimeType NetTimeType = ESampleNetTimeType::Local;
};SampleHttpTime.cpp
// Fill out your copyright notice in the Description page of Project Settings.#include "HttpTime/SampleHttpTime.h"#include "JsonObjectConverter.h"
#include "Async/Async.h"
#include "Async/TaskGraphInterfaces.h"USampleHttpTime::USampleHttpTime(const FObjectInitializer& ObjectInitializer) :Super(ObjectInitializer)
{
}USampleHttpTime::~USampleHttpTime()
{
}USampleHttpTime* USampleHttpTime::SampleHttpTimeAsyncAction(UObject* WorldContextObject, ESampleNetTimeType InNetTimeType)
{USampleHttpTime* AsyncAction = NewObject<USampleHttpTime>();AsyncAction->NetTimeType = InNetTimeType;AsyncAction->RegisterWithGameInstance(WorldContextObject);return AsyncAction;
}void USampleHttpTime::Activate()
{Super::Activate();AsyncTask(ENamedThreads::GameThread, [this]() {this->Activate_Internal();});FSampleNetTimeRespInfo RespInfo;Then.Broadcast(AsyncID, false, TEXT("USampleHttpTime is just started, please wait to be finished!"), RespInfo);}void USampleHttpTime::Activate_Internal()
{FString TimeServerURL = TEXT("");switch (NetTimeType){case ESampleNetTimeType::TaoBao:TimeServerURL = TEXT("https://acs.m.taobao.com/gw/mtop.common.getTimestamp/");break;case ESampleNetTimeType::Local:break;case ESampleNetTimeType::MaxNum:break;default:break;}if (!TimeServerURL.IsEmpty()) //如果TimeServerURL不是空字符串就使用网络时间，否则使用本地时间{SendHttp(TimeServerURL);return;}else{FSampleNetTimeRespInfo RespInfo;RespInfo.BeijingDateTime = FDateTime::Now();RespInfo.UTCDateTime = FDateTime::UtcNow();CallOnSuccess(AsyncID, true, TEXT("这是本地时间"), RespInfo);RealeaseResources();}
}void USampleHttpTime::SendHttp(const FString& InServerURL)
{FHttpRequestRef Request = FHttpModule::Get().CreateRequest();Request->OnProcessRequestComplete().BindUObject(this, &USampleHttpTime::OnHttpRespReceived);Request->SetURL(InServerURL);Request->SetVerb("Post");Request->SetHeader("Guid", AsyncID.ToString());Request->SetHeader("Content-Type", "application/json");Request->SetContentAsString(TEXT(""));Request->ProcessRequest();
}void USampleHttpTime::OnHttpRespReceived(FHttpRequestPtr HttpRequest, FHttpResponsePtr HttpResponse, bool bSucceeded)
{FString BackAsyncID = HttpRequest->GetHeader(TEXT("Guid"));FSampleNetTimeRespInfo RespInfo;if (bSucceeded && HttpRequest->GetStatus() == EHttpRequestStatus::Succeeded && HttpResponse->GetResponseCode() == 200){FString ResponseJson = HttpResponse->GetContentAsString();FSampleNetTimeRespMessage RespMessage;bool bParseJson = FJsonObjectConverter::JsonObjectStringToUStruct(ResponseJson, &RespMessage);if (bParseJson){FString TickString = RespMessage.data.t;int64 TickTime = FCString::Atoi64(*TickString) / 1000; //将时间戳字符串转换为 int64 类型，并将其转换为以秒为单位的时间戳RespInfo.UTCDateTime = FDateTime::FromUnixTimestamp(TickTime); //将时间戳转换为 FDateTime 类型的 UTC 时间RespInfo.BeijingDateTime = FDateTime::FromUnixTimestamp(TickTime + 8 * 60 * 60); //将时间戳转换为 FDateTime 类型的北京时间RespInfo.RawMessage = ResponseJson;RespInfo.RespMessage = RespMessage;CallOnSuccess(AsyncID, true, TEXT("Succeed!"), RespInfo);}}else{FString ErrorMessage = FString::Printf(TEXT("[%s],AsyncID:[%s],Receive NetTimeAsyncAction HttpResonpse Failed, Check Your Net"), *FString(__FUNCTION__), *(AsyncID.ToString()));UE_LOG(LogTemp, Error, TEXT("[%s]"), *ErrorMessage);CallOnFaild(AsyncID, false, ErrorMessage, RespInfo);}
}void USampleHttpTime::CallOnSuccess(FGuid InAsyncID, bool bInResult, FString InMessage, FSampleNetTimeRespInfo RespInfo)
{FSampleNetTimeDelegate TempDelegate = OnSuccess;AsyncTask(ENamedThreads::GameThread, [=]() {TempDelegate.Broadcast(InAsyncID, bInResult, InMessage, RespInfo);});
}void USampleHttpTime::CallOnFaild(FGuid InAsyncID, bool bInResult, FString InMessage, FSampleNetTimeRespInfo RespInfo)
{FSampleNetTimeDelegate TempDelegate = OnFail;AsyncTask(ENamedThreads::GameThread, [=]() {TempDelegate.Broadcast(InAsyncID, bInResult, InMessage, RespInfo);});
}void USampleHttpTime::RealeaseResources()
{Then.Clear();OnSuccess.Clear();OnFail.Clear();SetReadyToDestroy();
}
