原理

异步与多线程到底是怎么区分呢？江湖传闻，异步是目的，多线程是实现这个目的的方法。
那么，具体在ue4里面我们要去使用这两个东西呢？

异步一般用于资源的加载，事件的延迟响应。调用了一个开启异步方法的函数之后，程序就会在线程池里面寻找一些空闲线程对该函数进行处理。而该主线程继续往下走，不会发生阻塞
多线程一般用于信号的发送与接收，数据的计算等

实例

然后呢，异步在ue4中如何实现？本例采用获取资源的方式进行演示。

注：本例只演示如何编写异步代码，对于异步对功能的优化效果，应该在体量较大较频繁的操作中才可体现

建一个c++的ue4工程

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新建c++类

在这里插入图片描述

/////////=================.h// Fill out your copyright notice in the Description page of Project Settings.
#pragma once
#include "CoreMinimal.h"
#include "Components/ActorComponent.h"
#include "MyAsyncTaskActorComponent.generated.h"
UCLASS( ClassGroup=(Custom), meta=(BlueprintSpawnableComponent) )
class ASYNCTEST_API UMyAsyncTaskActorComponent : public UActorComponent
{
       GENERATED_BODY()
public:       
       // Sets default values for this component's properties
       UMyAsyncTaskActorComponent();
protected:
       // Called when the game starts
       virtual void BeginPlay() override;
public:       
       // Called every frame
       virtual void TickComponent(float DeltaTime, ELevelTick TickType,FActorComponentTickFunction* ThisTickFunction) override;
};
/////////=================.cpp
// Fill out your copyright notice in the Description page of Project Settings.
#include "MyAsyncTaskActorComponent.h"
// Sets default values for this component's properties
UMyAsyncTaskActorComponent::UMyAsyncTaskActorComponent()
{
       // Set this component to be initialized when the game starts, and to be ticked every frame.  You can turn these features
       // off to improve performance if you don't need them.
       PrimaryComponentTick.bCanEverTick = true;
       // ...
}
// Called when the game starts
void UMyAsyncTaskActorComponent::BeginPlay()
{
       Super::BeginPlay();
       // ...
}
// Called every frame
void UMyAsyncTaskActorComponent::TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction)
{
       Super::TickComponent(DeltaTime, TickType, ThisTickFunction);
       // ...
}

进行代码补充


/////////=================.h
// Fill out your copyright notice in the Description page of Project Settings.
#pragma once
#include "CoreMinimal.h"
#include "Components/ActorComponent.h"
#include <Runtime/CoreUObject/Public/UObject/NoExportTypes.h>
#include <Runtime/Engine/Classes/Engine/StreamableManager.h>
#include <Runtime/Engine/Classes/Engine/AssetManager.h>
#include "MyAsyncTaskActorComponent.generated.h"
UCLASS( ClassGroup=(Custom), meta=(BlueprintSpawnableComponent) )
class ASYNCTEST_API UMyAsyncTaskActorComponent : public UActorComponent
{
       GENERATED_BODY()
public:       
       // Sets default values for this component's properties
       UMyAsyncTaskActorComponent();
protected:
       // Called when the game starts
       virtual void BeginPlay() override;
public:       
       // Called every frame
       virtual void TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction) override;
       //=========定义委托,用于在项目中回调接受回调数据，这里采用多播形式========
       DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(FMyReceiveDelegateEvent, bool, result, UObject *, obj);
       //======声明委托======
       UPROPERTY(BlueprintAssignable, Category = "AsyncTask")
              FMyReceiveDelegateEvent MyReceiveDelegateEvent;
       //======定义一个资源路径======
       FSoftObjectPath assetPath;
       //======调用委托函数的执行===========
       UFUNCTION(BlueprintCallable, Category = "AsyncLoadAsset")
              void GetObjectByPath(const FString path);
       //定义一个用于执行异步的回调函数
       void GetObject();
       //定义一个同步调用方法
       UFUNCTION(BlueprintCallable, Category = "AsyncLoadAsset")
              UObject * GetObjectAsset(const FString path);
};
/////////=================.cpp
// Fill out your copyright notice in the Description page of Project Settings.
#include "MyAsyncTaskActorComponent.h"
// Sets default values for this component's properties
UMyAsyncTaskActorComponent::UMyAsyncTaskActorComponent()
{
       // Set this component to be initialized when the game starts, and to be ticked every frame.  You can turn these features
       // off to improve performance if you don't need them.
       PrimaryComponentTick.bCanEverTick = true;
       // ...
}
// Called when the game starts
void UMyAsyncTaskActorComponent::BeginPlay()
{
       Super::BeginPlay();
       // ...
       
}
// Called every frame
void UMyAsyncTaskActorComponent::TickComponent(float DeltaTime, ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction)
{
       Super::TickComponent(DeltaTime, TickType, ThisTickFunction);
       // ...
}
void UMyAsyncTaskActorComponent::GetObjectByPath(const FString path)
{
       assetPath = FSoftObjectPath(path);//进行实例化资源路径
       FStreamableManager& AssetLoader = UAssetManager::GetStreamableManager();
       AssetLoader.RequestAsyncLoad(assetPath, FStreamableDelegate::CreateUObject(this, &UMyAsyncTaskActorComponent::GetObject));
}
//=========注，小技巧，寻找到该路径下资源，返回的是uobject，即所有的父类，然后再根据需要转换回去
void UMyAsyncTaskActorComponent::GetObject()
{
       TSoftObjectPtr<UObject> ObjAsset(assetPath);
       UObject * obj = ObjAsset.Get();
       if (obj == nullptr)
       {
              MyReceiveDelegateEvent.Broadcast(false, nullptr);
              return;
       }
       MyReceiveDelegateEvent.Broadcast(true, obj);
}
UObject * UMyAsyncTaskActorComponent::GetObjectAsset(const FString path)
{
       UObject * obj = LoadObject<UObject >(NULL, *path);
       return obj;
}