UE4 C++ 用SaveGame类写一个异步加载关卡

首先，你需要创建一个继承自`USaveGame`的保存游戏数据的类，并在其中定义需要保存的数据成员。接下来，你需要在异步加载关卡时加载这些数据。

以下是一个简单的示例：

// MySaveGame.h
#pragma once

#include "CoreMinimal.h"
#include "GameFramework/SaveGame.h"
#include "MySaveGame.generated.h"

UCLASS()
class UMySaveGame : public USaveGame
{
    GENERATED_BODY()

public:
    UPROPERTY(BlueprintReadWrite)
    FString LevelName;
};

// MyLevelLoader.h
#pragma once

#include "CoreMinimal.h"
#include "Engine/LevelStreamingDynamic.h"
#include "MySaveGame.h"
#include "MyLevelLoader.generated.h"

UCLASS()
class AMyLevelLoader : public AActor
{
    GENERATED_BODY()

public:
    AMyLevelLoader();

    UFUNCTION(BlueprintCallable)
    void LoadLevelAsync(const FString& LevelName);

    void LoadLevelAsync_Internal(const FString& LevelName);

    UFUNCTION()
    void OnLevelLoaded();

private:
    UPROPERTY()
    ULevelStreamingDynamic* StreamingLevel;

    UPROPERTY()
    UMySaveGame* SaveGame;
};

// MyLevelLoader.cpp
#include "MyLevelLoader.h"
#include "Kismet/GameplayStatics.h"
#include "Engine/World.h"

AMyLevelLoader::AMyLevelLoader()
{
    PrimaryActorTick.bCanEverTick = false;

    StreamingLevel = NewObject<ULevelStreamingDynamic>(this, ULevelStreamingDynamic::StaticClass());
    StreamingLevel->bShouldBeLoaded = false;
    StreamingLevel->bShouldBeVisible = false;
}

void AMyLevelLoader::LoadLevelAsync(const FString& LevelName)
{
    SaveGame = Cast<UMySaveGame>(UGameplayStatics::CreateSaveGameObject(UMySaveGame::StaticClass()));

    if (SaveGame != nullptr)
    {
        SaveGame->LevelName = LevelName;
        SaveGame->SaveAsync(0);
    }

    FStreamableManager& Streamable = UAssetManager::GetStreamableManager();
    Streamable.RequestLevel(StreamingLevel->GetWorldAssetPackageFName(LevelName), FStreamableDelegate::CreateUObject(this, &AMyLevelLoader::LoadLevelAsync_Internal, LevelName));
}

void AMyLevelLoader::LoadLevelAsync_Internal(const FString& LevelName)
{
    StreamingLevel->SetWorldAssetByPackageName(LevelName);
    StreamingLevel->bShouldBeLoaded = true;

    UWorld* World = GetWorld();
    if (World != nullptr)
    {
        StreamingLevel->LevelColor = FColor::MakeRandomColor();
        StreamingLevel->LevelTransform = FTransform(FRotator::ZeroRotator, FVector(0.f, 0.f, 0.f), FVector(1.f, 1.f, 1.f));
        World->AddLevelStreamingActor(StreamingLevel, GetActorTransform());
    }
}

void AMyLevelLoader::OnLevelLoaded()
{
    if (SaveGame != nullptr)
    {
        FString LevelName = SaveGame->LevelName;
        SaveGame->Delete();
        SaveGame = nullptr;

        // Do something with the loaded level...
    }
}

在上面的示例中，`UMySaveGame`保存了需要在异步加载关卡时加载的数据成员。`AMyLevelLoader`是一个继承自`AActor`的类，它有一个`LoadLevelAsync`函数，它会异步加载指定名称的关卡，并在加载完成后调用`OnLevelLoaded`函数。在`LoadLevelAsync_Internal`函数中，我们使用`ULevelStreamingDynamic`类来加载关卡，并在加载完成后将其添加到世界中。在`OnLevelLoaded`函数中，我们可以获取保存在`UMySaveGame`对象中的数据成员，并进行后续操作。

请注意，以上示例仅用于演示目的，实际使用时可能需要进行更多的错误处理和数据验证。