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03-UnrealEngine/Gameplay/GAS/(16)在联机项目中使用GAS的注意点.md
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03-UnrealEngine/Gameplay/GAS/(16)在联机项目中使用GAS的注意点.md
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## 前言
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大多数人应该是会通过学习UE4的ActionRPG项目来入门GAS框架的。但在最近自己做Demo的过程中才发现里面的部分不适用网络联机。比如ActionRPG将Character与Controller的指针存在GameMode，因为Server与Client只有一个GameMode的关系，就不符合多人联机游戏的规则。所以在经过实践之后这里我分享一些要点仅供抛砖引玉。这里我再推荐各位读者去看一下GASDocument以及附带的工程，它展现了正确的设计思路。
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## Ability中的网络同步节点
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WaitNetSync
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## GASDocument中的处理方式
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将AbilitySystemComponent以及AttributeSet放在PlayerState中，之后再Character类中的PossesseBy()事件(ServerOnly)与OnRep_PlayerState()事件(Client)给角色类的ASC弱智能指针与AttributeSet弱智能指针赋值。
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```
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AGDPlayerState::AGDPlayerState()
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{
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AbilitySystemComponent = CreateDefaultSubobject<UGDAbilitySystemComponent>(TEXT("AbilitySystemComponent"));
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AbilitySystemComponent->SetIsReplicated(true);
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// Mixed mode means we only are replicated the GEs to ourself, not the GEs to simulated proxies. If another GDPlayerState (Hero) receives a GE,
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// we won't be told about it by the Server. Attributes, GameplayTags, and GameplayCues will still replicate to us.
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AbilitySystemComponent->SetReplicationMode(EGameplayEffectReplicationMode::Mixed);
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AttributeSetBase = CreateDefaultSubobject<UGDAttributeSetBase>(TEXT("AttributeSetBase"));
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NetUpdateFrequency = 100.0f;
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}
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// TWeakObjectPtr<class UGDAbilitySystemComponent> AbilitySystemComponent;
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// TWeakObjectPtr<class UGDAttributeSetBase> AttributeSetBase;
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// Server only
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void AGDHeroCharacter::PossessedBy(AController * NewController)
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{
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Super::PossessedBy(NewController);
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AGDPlayerState* PS = GetPlayerState<AGDPlayerState>();
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if (PS)
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{
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// Set the ASC on the Server. Clients do this in OnRep_PlayerState()
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AbilitySystemComponent = Cast<UGDAbilitySystemComponent>(PS->GetAbilitySystemComponent());
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// AI won't have PlayerControllers so we can init again here just to be sure. No harm in initing twice for heroes that have PlayerControllers.
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PS->GetAbilitySystemComponent()->InitAbilityActorInfo(PS, this);
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AttributeSetBase = PS->GetAttributeSetBase();
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}
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//...
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}
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// Client only
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void AGDHeroCharacter::OnRep_PlayerState()
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{
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Super::OnRep_PlayerState();
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AGDPlayerState* PS = GetPlayerState<AGDPlayerState>();
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if (PS)
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{
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// Set the ASC for clients. Server does this in PossessedBy.
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AbilitySystemComponent = Cast<UGDAbilitySystemComponent>(PS->GetAbilitySystemComponent());
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// Init ASC Actor Info for clients. Server will init its ASC when it possesses a new Actor.
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AbilitySystemComponent->InitAbilityActorInfo(PS, this);
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AttributeSetBase = PS->GetAttributeSetBase();
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}
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// ...
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}
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```
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## 预测
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## PlayerState
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PlayerState只在开发多人游戏时有用，在设计上负责管理角色的变量(PlayerId、UniqueId、SessionName与自己定义的变量)。
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### 指定与初始化
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在GameMode中设置实现的PlayerState类，之后在AController::InitPlayerState()中Spawn。
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### 访问方法
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- Pawn->PlayerState
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- Controller->PlayerState(一般用这个)
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另外还可以通过GameState->PlayerArray获取所有有效的GameState实例。
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### PlayerState
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PlayerState在切换地图时会默认销毁，为了解决这个问题可以通过实现CopyProperties方法来解决。
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```
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class ARPGPlayerState : public APlayerState
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{
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GENERATED_BODY()
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public:
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UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "ActionRPG")
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ARPGCharacterBase* Character;
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protected:
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/** 这里是为了解决切换地图时的属性丢失问题 */
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/** Copy properties which need to be saved in inactive PlayerState */
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virtual void CopyProperties(APlayerState* PlayerState);
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};
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```
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```
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void ARPGPlayerState::CopyProperties(APlayerState* PlayerState)
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{
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//如果不是因为断线
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if (IsFromPreviousLevel())
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{
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ARPGPlayerState* RPGPlayerState=Cast<ARPGPlayerState>(PlayerState);
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RPGPlayerState->Character = Character;
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}
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}
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```
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### NetUpdateFrequency
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PlayerState的NetUpdateFrequency和角色类的效果是一样的，都是调节更新频率。默认数值对于GAS太低了，会导致滞后性。100是个比较高的数值，你也可以按照需求自己调节。
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## Controller
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### 获取PlayerControllers
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- GetWorld()->GetPlayerControllerIterator()
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- PlayerState->GetOwner()
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- Pawn->GetController()
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### BeginPlay里不做任何与GAS相关的操作
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因为在服务端，Possession会发生在在BeginPlay前，客户端Possession发生在BeginPlay后，所以我们不能在BeginPlay中写任何有关ASC的逻辑除非PlayerState已经同步。
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### 相关判断服务端客户端状态函数
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在Ability类中一些操作可能需要判断是服务端还是客户端，比如应用GameplayEffect就在服务端执行(使用HasAuthority())，而创建UI就需要在客户端执行(使用IsLocallyControlled())。
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#### 蓝图
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- HasAuthority()判断是否是服务端或是作为主机的玩家
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- IsLocallyControlled()判断是否是本地控制器
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- IsServer()通过World的ENetMode来段是服务端
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#### c++
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- 蓝图函数HasAuthority()在c++中为`return (GetLocalRole() == ROLE_Authority);`
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- IsLocallyControlled(),c++中有对应函数。
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## NetSecurityPolicy
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GameplayAbility的网络安全策略决定了Ability应该在网络的何处执行. 它为尝试执行限制Ability的客户端提供了保护.
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- ClientOrServer：没有安全需求. 客户端或服务端可以自由地触发该Ability的执行和终止.
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- ServerOnlyExecution：客户端对该Ability请求的执行会被服务端忽略, 但客户端仍可以请求服务端取消或结束该Ability.
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- ServerOnlyTermination：客户端对该Ability请求的取消或结束会被服务端忽略, 但客户端仍可以请求执行该Ability.
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- ServerOnly：服务端控制该Ability的执行和终止, 客户端的任何请求都会被忽略.
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## NetExecutionPolicy
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推荐看这位大佬的文章：https://zhuanlan.zhihu.com/p/143637846
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## 属性集属性UI更新
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这里推荐使用GASDocument中的GameplayTasks更新方法。
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```
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#pragma once
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#include "CoreMinimal.h"
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#include "Kismet/BlueprintAsyncActionBase.h"
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#include "AbilitySystemComponent.h"
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#include "AsyncTaskAttributeChanged.generated.h"
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DECLARE_DYNAMIC_MULTICAST_DELEGATE_ThreeParams(FOnAttributeChanged, FGameplayAttribute, Attribute, float, NewValue, float, OldValue);
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/**
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* Blueprint node to automatically register a listener for all attribute changes in an AbilitySystemComponent.
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* Useful to use in UI.
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*/
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UCLASS(BlueprintType, meta=(ExposedAsyncProxy = AsyncTask))
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class RPGGAMEPLAYABILITY_API UAsyncTaskAttributeChanged : public UBlueprintAsyncActionBase
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{
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GENERATED_BODY()
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public:
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UPROPERTY(BlueprintAssignable)
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FOnAttributeChanged OnAttributeChanged;
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// Listens for an attribute changing.
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UFUNCTION(BlueprintCallable, meta = (BlueprintInternalUseOnly = "true"))
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static UAsyncTaskAttributeChanged* ListenForAttributeChange(UAbilitySystemComponent* AbilitySystemComponent, FGameplayAttribute Attribute);
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// Listens for an attribute changing.
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// Version that takes in an array of Attributes. Check the Attribute output for which Attribute changed.
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UFUNCTION(BlueprintCallable, meta = (BlueprintInternalUseOnly = "true"))
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static UAsyncTaskAttributeChanged* ListenForAttributesChange(UAbilitySystemComponent* AbilitySystemComponent, TArray<FGameplayAttribute> Attributes);
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// You must call this function manually when you want the AsyncTask to end.
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// For UMG Widgets, you would call it in the Widget's Destruct event.
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UFUNCTION(BlueprintCallable)
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void EndTask();
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protected:
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UPROPERTY()
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UAbilitySystemComponent* ASC;
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FGameplayAttribute AttributeToListenFor;
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TArray<FGameplayAttribute> AttributesToListenFor;
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void AttributeChanged(const FOnAttributeChangeData& Data);
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};
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```
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```
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#include "Abilities/AsyncTasks/AsyncTaskAttributeChanged.h"
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UAsyncTaskAttributeChanged* UAsyncTaskAttributeChanged::ListenForAttributeChange(UAbilitySystemComponent* AbilitySystemComponent, FGameplayAttribute Attribute)
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{
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UAsyncTaskAttributeChanged* WaitForAttributeChangedTask = NewObject<UAsyncTaskAttributeChanged>();
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WaitForAttributeChangedTask->ASC = AbilitySystemComponent;
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WaitForAttributeChangedTask->AttributeToListenFor = Attribute;
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if (!IsValid(AbilitySystemComponent) || !Attribute.IsValid())
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{
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WaitForAttributeChangedTask->RemoveFromRoot();
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return nullptr;
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}
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AbilitySystemComponent->GetGameplayAttributeValueChangeDelegate(Attribute).AddUObject(WaitForAttributeChangedTask, &UAsyncTaskAttributeChanged::AttributeChanged);
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return WaitForAttributeChangedTask;
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}
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UAsyncTaskAttributeChanged * UAsyncTaskAttributeChanged::ListenForAttributesChange(UAbilitySystemComponent * AbilitySystemComponent, TArray<FGameplayAttribute> Attributes)
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{
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UAsyncTaskAttributeChanged* WaitForAttributeChangedTask = NewObject<UAsyncTaskAttributeChanged>();
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WaitForAttributeChangedTask->ASC = AbilitySystemComponent;
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WaitForAttributeChangedTask->AttributesToListenFor = Attributes;
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if (!IsValid(AbilitySystemComponent) || Attributes.Num() < 1)
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{
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WaitForAttributeChangedTask->RemoveFromRoot();
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return nullptr;
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}
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for (FGameplayAttribute Attribute : Attributes)
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{
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AbilitySystemComponent->GetGameplayAttributeValueChangeDelegate(Attribute).AddUObject(WaitForAttributeChangedTask, &UAsyncTaskAttributeChanged::AttributeChanged);
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}
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return WaitForAttributeChangedTask;
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}
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void UAsyncTaskAttributeChanged::EndTask()
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{
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if (IsValid(ASC))
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{
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ASC->GetGameplayAttributeValueChangeDelegate(AttributeToListenFor).RemoveAll(this);
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for (FGameplayAttribute Attribute : AttributesToListenFor)
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{
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ASC->GetGameplayAttributeValueChangeDelegate(Attribute).RemoveAll(this);
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}
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}
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SetReadyToDestroy();
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MarkPendingKill();
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}
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void UAsyncTaskAttributeChanged::AttributeChanged(const FOnAttributeChangeData & Data)
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{
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OnAttributeChanged.Broadcast(Data.Attribute, Data.NewValue, Data.OldValue);
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}
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```
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