## 前言
本人最近看了GameplayAbility的wiki与官方的ActionRPG案例，大致对此有了一定了解。所以在此分享相关经验顺便作为学习笔记。

wiki采用了第三人称模板来进行讲解。讲解了几个主要类的概念、参数以及用法。

ActionRPG则是一个较为完整的案例：它通过c++ 往几个GameplayAbility的基础类中添加了若干逻辑，使得之更加适合于RPG项目。大部分改动都很不错，甚至直接复制，让它作为你的RPG模板都是没问题。它的主要逻辑以及表现都在于蓝图中(技能与效果)，所以它也是一个c++与蓝图结合开发的好例子。(注意：GameAbility无法完全通过蓝图开发)

所以接下来我也会适当讲解actionRPG的结构。<br>
注意：有关网络同步的我都会略过。
## 相关资料
wiki：
https://wiki.unrealengine.com/index.php?title=GameplayAbilities_and_You#Common_Issues

GameplayAbility文档：
https://docs.unrealengine.com/en-us/Gameplay/GameplayAbilitySystem

actionRPG案例文章：
https://docs.unrealengine.com/en-US/Resources/SampleGames/ARPG/index.html

## 启用GameAbility插件并且在你的项目中添加该模块
1. 在编辑（Edit）->插件（Plugins）找到Gameplay Ability 并启用。
2. 在你的c++项目(ProjectName).Build.cs文件的PublicDependencyModuleNames变量中添加： "GameplayAbilities", "GameplayTags", "GameplayTasks"。

例如：
```
PublicDependencyModuleNames.AddRange(new string[] { "GameplayAbilities", "GameplayTags", "GameplayTasks", "Core", "CoreUObject", "Engine", "InputCore", "HeadMountedDisplay" });
```
### 注意事项
**在模块文件以及c++中包含GameplayBility前，先需要确定是否在项目中启用GameplayAbility插件（默认是不启用的）。不然你的项目编译时会通过，但运行时会显示无法加载游戏模块。**
## 建议
在模块h文件与cpp中定义这个模块的log标签，这样你可以对log进行过滤显示。
```
//在h文件中
ACTIONRPG_API DECLARE_LOG_CATEGORY_EXTERN(LogActionRPG, Log, All);
```
```
//在cpp文件中
DEFINE_LOG_CATEGORY(LogActionRPG);
```
## 在角色类中挂载自定义的UGameplayAbilityComponent
actionRPG中定义了URPGAbilitySystemComponent作为挂载组件类，它实现了以下函数：
```
//通过Tag（可以是多个tag）来获取激活的技能
void GetActiveAbilitiesWithTags(const FGameplayTagContainer& GameplayTagContainer, TArray<URPGGameplayAbility*>& ActiveAbilities);
//取得角色等级，这个意义不大，因为不是所有的rpg游戏都有等级这一说
int32 GetDefaultAbilityLevel() const;
//通过全局的AbilitySystem来获取对应Actor所绑定的组件指针
static URPGAbilitySystemComponent* GetAbilitySystemComponentFromActor(const AActor* Actor, bool LookForComponent = false);
```
```
void URPGAbilitySystemComponent::GetActiveAbilitiesWithTags(const FGameplayTagContainer& GameplayTagContainer, TArray<URPGGameplayAbility*>& ActiveAbilities)
{
	TArray<FGameplayAbilitySpec*> AbilitiesToActivate;
	GetActivatableGameplayAbilitySpecsByAllMatchingTags(GameplayTagContainer, AbilitiesToActivate, false);

	for (FGameplayAbilitySpec* Spec : AbilitiesToActivate)
	{
		TArray<UGameplayAbility*> AbilityInstances = Spec->GetAbilityInstances();

		for (UGameplayAbility* ActiveAbility : AbilityInstances)
		{
			ActiveAbilities.Add(Cast<URPGGameplayAbility>(ActiveAbility));
		}
	}
}

URPGAbilitySystemComponent* URPGAbilitySystemComponent::GetAbilitySystemComponentFromActor(const AActor* Actor, bool LookForComponent)
{
	return Cast<URPGAbilitySystemComponent>(UAbilitySystemGlobals::GetAbilitySystemComponentFromActor(Actor, LookForComponent));
}
```

## 定义角色类
ARPGCharacterBase继承于ACharacter与接口类IAbilitySystemInterface。

actionRPG中定义了ARPGCharacterBase作为角色类的基础类。因为这个类会适用于主角、友善NPC、敌方NPC，所有我们不应该在这个类中进行输入绑定、以及各种Camera、movementComponent等非共用性组件的绑定与设置。

接下来我会讲解我阅读代码的顺序，具体代码可以就请读者参考actionRPG。
首先
```
//GameplayAbilityComponent指针
class URPGAbilitySystemComponent* AbilitySystemComponent;
//因为继承IAbilitySystemInterface所以需要实现这个接口
virtual UAbilitySystemComponent* GetAbilitySystemComponent() const override;
//用以判断这个Actor是否初始化了GameplayAbilityComponent
bool bAbilitiesInitialized;
//用于存储GameplayAbility（角色技能）的容器，并且会在游戏开始时向AbilitySystemComponent进行注册
//读者可以在看了我下一篇文章再添加
TArray<TSubclassOf<URPGGameplayAbility>> GameplayAbilities;
```
除此之外，actionRPG还重写了PossessedBy，以此来实现向AbilitySystemComponent注册Ability的功能。Wiki上的教程选择在Beginplay事件中进行注册，之后再PossessedBy中进行刷新（判断技能TArray是否有变化，如果有就进行相应得修改）。在本教程中，我选择actionRPG的方案。
```
ARPGCharacterBase::ARPGCharacterBase()
{
	AbilitySystemComponent = CreateDefaultSubobject<URPGAbilitySystemComponent>(TEXT("AbilitySystemComponent"));

	bAbilitiesInitialized = false;
}

void ARPGCharacterBase::AddStartupGameplayAbilities()
{
	if (!bAbilitiesInitialized)
	{
		for (TSubclassOf<URPGGameplayAbility>& StartupAbility : GameplayAbilities)
		{
			AbilitySystemComponent->GiveAbility(FGameplayAbilitySpec(StartupAbility,1,INDEX_NONE,this));
		}
		bAbilitiesInitialized = true;

		UE_LOG(LogActionRPG, Warning, TEXT("%s"), *FString("All Ablities registered"));
	}
}

//RemoveStartupGameplayAbilities在actionRPG中的SetCharacterLevel函数中被调用
//但这个函数和GameplayAbility框架关系不大，我就省略了
void ARPGCharacterBase::RemoveStartupGameplayAbilities()
{
	if (bAbilitiesInitialized)
	{
		TArray<FGameplayAbilitySpecHandle> AbilitiesToRemove;
		for (const FGameplayAbilitySpec& Spec : AbilitySystemComponent->GetActivatableAbilities())
		{
			if ((Spec.SourceObject == this) && GameplayAbilities.Contains(Spec.Ability->GetClass()))
			{
				AbilitiesToRemove.Add(Spec.Handle);
			}
		}

		for (int32 i = 0; i < AbilitiesToRemove.Num(); i++)
		{
			AbilitySystemComponent->ClearAbility(AbilitiesToRemove[i]);
		}
		bAbilitiesInitialized = false;
	}
}

void ARPGCharacterBase::PossessedBy(AController* NewController)
{
	Super::PossessedBy(NewController);
	if (AbilitySystemComponent)
	{
		AddStartupGameplayAbilities();
		AbilitySystemComponent->InitAbilityActorInfo(this, this);
	}
}
```
## UAbilitySystemComponent中的委托
```
/** Used to register callbacks to ability-key input */
DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FAbilityAbilityKey, /*UGameplayAbility*, Ability, */int32, InputID);

/** Used to register callbacks to confirm/cancel input */
DECLARE_DYNAMIC_MULTICAST_DELEGATE(FAbilityConfirmOrCancel);

/** Delegate for when an effect is applied */
DECLARE_MULTICAST_DELEGATE_ThreeParams(FOnGameplayEffectAppliedDelegate, UAbilitySystemComponent*, const FGameplayEffectSpec&, FActiveGameplayEffectHandle);

/** Called on server whenever a GE is applied to self. This includes instant and duration based GEs. */
FOnGameplayEffectAppliedDelegate OnGameplayEffectAppliedDelegateToSelf;

/** Called on server whenever a GE is applied to someone else. This includes instant and duration based GEs. */
FOnGameplayEffectAppliedDelegate OnGameplayEffectAppliedDelegateToTarget;

/** Called on both client and server whenever a duraton based GE is added (E.g., instant GEs do not trigger this). */
FOnGameplayEffectAppliedDelegate OnActiveGameplayEffectAddedDelegateToSelf;

/** Called on server whenever a periodic GE executes on self */
FOnGameplayEffectAppliedDelegate OnPeriodicGameplayEffectExecuteDelegateOnSelf;

/** Called on server whenever a periodic GE executes on target */
FOnGameplayEffectAppliedDelegate OnPeriodicGameplayEffectExecuteDelegateOnTarget;

/** Register for when an attribute value changes */
FOnGameplayAttributeValueChange& GetGameplayAttributeValueChangeDelegate(FGameplayAttribute Attribute);

/** Callback anytime an ability is ended */
FAbilityEnded AbilityEndedCallbacks;

/** Called with a failure reason when an ability fails to execute */
FAbilityFailedDelegate AbilityFailedCallbacks;
```