一 UE4的加载模式

在切换关卡时，常常会因为关卡资源过大，造成卡顿，黑屏，那是因为资源过大导致主线程堵塞，引起界面黑屏卡顿，如果使用streamingLevel加载的loading方式，依然无法根本解决线程堵塞问题，这时候就需要用UE4的预加载过程，来开启单独的线程解决这个问题。

二加载屏幕将具有的所属性的结构FLoadingScreenAttributes

FLoadingScreenAttributes LoadingScreen;

LoadingScreen.bAutoCompleteWhenLoadingCompletes = false;//是否在播放完所有电影并完成加载后，加载屏幕将消失
LoadingScreen.bWaitForManualStop = false;//是否一直播放movies,直到手动停止LoadingScreen.bMoviesAreSkippable = false;//是否加载完成，通过单击加载屏幕来跳过电影

LoadingScreen.MinimumLoadingScreenDisplayTime = 3.0f; // movie最少播放时间
LoadingScreen.PlaybackType = EMoviePlaybackType::MT_Looped;//是否循环

三代码操作

一、创建C++类，GameInstance

二、在你的项目的Build.cs中加入模块

"HeadMountedDisplay",
"MoviePlayer",
"UMG", "Slate", "SlateCore"

三、在MyGameInstance.h文件中

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "CoreMinimal.h"
#include "Engine/GameInstance.h"
#include "Runtime/UMG/Public/UMG.h"
#include "Runtime/UMG/Public/UMGStyle.h"
#include "Runtime/UMG/Public/Slate/SObjectWidget.h"
#include "Runtime/UMG/Public/IUMGModule.h"
#include "Runtime/UMG/Public/Blueprint/UserWidget.h"
#include "Runtime/MoviePlayer/Public/MoviePlayer.h"
#include "Runtime/SlateCore/Public/Widgets/SWidget.h"
#include "MyGameInstance.generated.h"

/**
 * 
 */
UCLASS()
class LOADINGSCREEN_API UMyGameInstance : public UGameInstance
{
	GENERATED_BODY()
public:
	virtual void Init() override;

	UFUNCTION()
		virtual void BeginLoadingScreen(const FString& MapName);
	UFUNCTION()
		virtual void EndLoadingScreen(UWorld* LoadedWorld);

	UPROPERTY()
		UUserWidget* CurrentWidget;
	// loading widget
	UPROPERTY(EditAnywhere, BlueprintReadOnly, Category = "UMGGame")
		TSubclassOf<UUserWidget> LoadingWidget;

};

四、在MyGameInstance.cpp文件中

// Fill out your copyright notice in the Description page of Project Settings.


#include "MyGameInstance.h"

void UMyGameInstance::Init()
{
    Super::Init();

    FCoreUObjectDelegates::PreLoadMap.AddUObject(this, &UMyGameInstance::BeginLoadingScreen);
    FCoreUObjectDelegates::PostLoadMapWithWorld.AddUObject(this,&UMyGameInstance::EndLoadingScreen);
}

void UMyGameInstance::BeginLoadingScreen(const FString& MapName)
{
	FLoadingScreenAttributes LoadingScreen;

	LoadingScreen.bAutoCompleteWhenLoadingCompletes = false;//是否在播放完所有电影并完成加载后，加载屏幕将消失
	LoadingScreen.bWaitForManualStop = false;//是否一直播放movies,直到手动停止
	LoadingScreen.bMoviesAreSkippable = false;//是否加载完成，就可以通过单击加载屏幕来跳过电影
	LoadingScreen.MinimumLoadingScreenDisplayTime = 3.0f; // movie最少播放时间
	//LoadingScreen.PlaybackType = EMoviePlaybackType::MT_Looped;

	LoadingScreen.WidgetLoadingScreen = FLoadingScreenAttributes::NewTestLoadingScreenWidget(); // movie不存在时，显示的widget

	if (LoadingWidget != nullptr)
	{
		CurrentWidget = CreateWidget<UUserWidget>(this, LoadingWidget);
		TSharedPtr<SWidget> LoadScreen = CurrentWidget->TakeWidget();
		LoadingScreen.WidgetLoadingScreen = LoadScreen;
	}
	else
	{
		UE_LOG(LogTemp, Warning, TEXT("LoadingWidget == nullptr"));
	}
	//LoadingScreen.MoviePaths.Add("squad_intro_movie");
	GetMoviePlayer()->SetupLoadingScreen(LoadingScreen);
}

void UMyGameInstance::EndLoadingScreen(UWorld* LoadedWorld)
{
	UE_LOG(LogTemp,Warning,TEXT("LoadSuccess"));
	GetMoviePlayer()->StopMovie();
}

五、在蓝图中设置一下项目设置，创建Gameinstance 蓝图