UE4 C++ 类的4种引用类型，和异步加载资产

4种引用类型

	对象引用：引用 World 的实例对象。

就是直接定义

UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//对象引用
	UWorld* LoadPackageSoftObjectPath4;

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	类引用：引用从 World 继承而来的类。

TSubclassOf 是提供 UClass 类型安全性的模板类
允许在类型安全的情况下传递 TClassType 的模板

UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//类引用
	TSubclassOf<UWorld>LoadPackageSoftObjectPath3;

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软类引用：从类型的 World 继承的类的路径，该类型可能不会被加载。可用于异步加载类。

TSoftClassPtr是 FSoftObjectPtr 的模板化包装器，其工作方式类似于TSubclassOf，它可以在 UProperties 中用于蓝图子类

UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//软类引用
	TSoftClassPtr<UWorld> LoadPackageSoftObjectPath2;

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	软对象引用: 类型为 World 的实例Object的路径，该类型可能不会被加载。可用于异步加载资产。

TSoftObjectPtr是通用FSoftObjectPtr的模板化包装器，可以在 UProperties 中使用

UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//软对象引用
	TSoftObjectPtr<UWorld> LoadPackageSoftObjectPath;

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异步加载资产，这里异步加载关卡，打开关卡

C++类的游戏模式基础：

// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/GameModeBase.h"
#include "LoadLevelGameModeBase.generated.h"

/**
 * 
 */
UCLASS()
class LOADLEVEL_API ALoadLevelGameModeBase : public AGameModeBase
{
	GENERATED_BODY()
public:
	bool bIsLoaded;

	UPROPERTY()
	FString LoadPackagePath;

	UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//软对象引用
	TSoftObjectPtr<UWorld> LoadPackageSoftObjectPath;

	UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//软类引用
	TSoftClassPtr<UWorld> LoadPackageSoftObjectPath2;
	
	UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//类引用
	TSubclassOf<UWorld>LoadPackageSoftObjectPath3;

	UPROPERTY(EditAnywhere,BlueprintReadOnly,Category="My")//对象引用
	UWorld* LoadPackageSoftObjectPath4;
	
	// 用于加载完成的回调
	DECLARE_DYNAMIC_DELEGATE(FOnAsyncLoadFinished);
public:
	UFUNCTION(BlueprintCallable,Category="My")
	void MyAsyncLoad(const FOnAsyncLoadFinished& OnAsyncLoadFinished);
	
	UFUNCTION(BlueprintCallable,Category="My")
	float GetLoadProgress();

};

// Copyright Epic Games, Inc. All Rights Reserved.


#include "LoadLevelGameModeBase.h"

//开始异步加载

void ALoadLevelGameModeBase::MyAsyncLoad(const FOnAsyncLoadFinished& OnAsyncLoadFinished)
{
	//不使用GetBaseFilename，编译 error C4458: LoadPackageAsync failed to begin to load a package···
	LoadPackagePath = FPaths::GetBaseFilename(LoadPackageSoftObjectPath.ToString(), false);
	bIsLoaded = false;
	UE_LOG(LogTemp, Warning, TEXT("String: %s"), *LoadPackagePath);
	
	LoadPackageAsync(
		LoadPackagePath,
		FLoadPackageAsyncDelegate::CreateLambda([=](const FName& PackageName, UPackage* LoadedPackage, EAsyncLoadingResult::Type Result)
			{
			 //开始
				if (Result == EAsyncLoadingResult::Failed)
				{
					UE_LOG(LogTemp, Warning, TEXT("Load Failed"));
				}
				else if (Result == EAsyncLoadingResult::Succeeded)//加载完毕
					{
						bIsLoaded = true;
						UE_LOG(LogTemp, Warning, TEXT("Load Succeeded"));
						OnAsyncLoadFinished.ExecuteIfBound();//调用绑定的事件，
					}
			}
		), 0, PKG_ContainsMap);
}

//获取加载的进度 -1 —— 100
float ALoadLevelGameModeBase::GetLoadProgress()
{
		float FloatPercentage = GetAsyncLoadPercentage(*LoadPackagePath);
		if (!bIsLoaded)
		{
			FString ResultStr = FString::Printf(TEXT("Percentage: %f"), FloatPercentage);
			GEngine->AddOnScreenDebugMessage(-1, 2.0f, FColor::Green, ResultStr);
			UE_LOG(LogTemp, Warning, TEXT("Percentage: %f"), FloatPercentage);
		}
		else
		{
			FloatPercentage = 100;
		}
		return FloatPercentage;
}

这个是开始加载和加载完成

namespace EAsyncLoadingResult
{
	enum Type
	{
		/** Package failed to load */
		Failed,
		/** Package loaded successfully */
		Succeeded,
		/** Async loading was canceled */
		Canceled
	};
}

主要看LoadPackageAsync这个函数的使用：

了解后用生成一个继承游戏模式基础的蓝图类
在蓝图类里调用和赋初值

加载完后打开关卡就行了