【UE4 C++ 基础知识】<9> Interface 接口

概述

• 简单的说，接口提供一组公共的方法，不同的对象中继承这些方法后可以有不同的具体实现。
• 任何使用接口的类都必须实现这些接口。
• 实现解耦
• 解决多继承的问题

蓝图使用

使用方法

三种调用方法的区别

调用流关卡蓝图的接口函数

C++ 使用接口

本例使用一个Box Trigger 出发overlap 调用 Drone实例的接口

添加接口类

定义接口

声明蓝图可调用接口函数

• 用UFUNCTION 宏 BlueprintCallable 声明蓝图可调用，还必须使用 BlueprintImplementableEvent 或 BlueprintNativeEvent 说明，而且函数不能为虚函数

• 如果不想蓝图重载，只是想使用 BlueprintCallable 以支持蓝图起到单纯的调用作用，可以通过将接口标记为 UINTERFACE(meta = (CannotImplementInterfaceInBlueprint)) 来解决

• 通过声明 virtual 虚函数，使得派生类可重载

代码

• ReactToTriggerInterface.h

  #pragma once
  #include "CoreMinimal.h"
  #include "UObject/Interface.h"
  #include "ReactToTriggerInterface.generated.h"
  
  // 无需更改
  // UINTERFACE类不是实际的接口；它是一个空白类，它的存在只是为了向虚幻引擎反射系统确保可见性。
  UINTERFACE(MinimalAPI)
  class UReactToTriggerInterface : public UInterface
  {
  	GENERATED_BODY()
  };
  
  //开头字母"U"必须改为"I"。
  class TIPS_API IReactToTriggerInterface
  {
  	GENERATED_BODY()
  
  public:
  
  	// 纯虚函数，实现类必须实现接口
  	virtual void ReactToTrigger_PureVirtual() = 0;
  
  	// 虚函数，在接口本身的 .h 或 .cpp 文件中提供默认实现.实现类可覆盖
  	virtual void ReactToTrigger_Virtual();
  
  	//实现类可以在蓝图和C++中实现接口
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category="Trigger Reaction")
  		void ReactToTrigger_NativeEvent1(int32 number);
  
  	//实现类可以在蓝图和C++中实现接口
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category = "Trigger Reaction")
  		bool ReactToTrigger_NativeEvent2(int32 number);
  
  	//实现类在蓝图中实现接口
  	UFUNCTION(BlueprintCallable, BlueprintImplementableEvent, Category = "Trigger Reaction")
  		void ReactToTrigger_ImplementableEvent();
  };
  

• ReactToTriggerInterface.cpp

  #include "ReactToTriggerInterface.h"
  void IReactToTriggerInterface::ReactToTrigger_Virtual()
  {
  	// unimplemented(); //该宏将在执行代码行时发出调试语句, 中断
  	UE_LOG(LogTemp, Warning, TEXT("ReactToTrigger_Virtual 被调用, From 接口本身"));
  }
  

实现接口

• MyDrone.h 此类继承自Pawn类，无关本文主题

  #include "ReactToTriggerInterface.h"
  #include "MyDrone.generated.h"
  
  UCLASS()
  class TIPS_API AMyDrone : public ADrone, public IReactToTriggerInterface
  {
  	GENERATED_BODY()
  
  public:
  	virtual void ReactToTrigger_PureVirtual() override;
  
  	//可蓝图调用，貌似通用写法
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category = "Trigger Reaction")
  		void ReactToTrigger_NativeEvent1(int32 number);
  		virtual void ReactToTrigger_NativeEvent1_Implementation(int32 number) override;
  
  	//蓝图可调用,,貌似和上面没区别
  	virtual bool ReactToTrigger_NativeEvent2_Implementation(int32 number) override;
  
  	//void ReactToTrigger_ImplementableEvent();需要在蓝图实现
  };
  

• MyDrone.cpp

  #include "MyDrone.h"
  
  void AMyDrone::ReactToTrigger_PureVirtual()
  {
  	UE_LOG(LogTemp, Warning, TEXT("ReactToTrigger_PureVirtual 被调用, From MyDrone"));
  }
  
  void AMyDrone::ReactToTrigger_NativeEvent1_Implementation(int32 number)
  {
  	UE_LOG(LogTemp, Warning, TEXT("ReactToTrigger_NativeEvent1 被调用, From MyDrone"));
  }
  
  bool AMyDrone::ReactToTrigger_NativeEvent2_Implementation(int32 number)
  {
  	UE_LOG(LogTemp, Warning, TEXT("ReactToTrigger_NativeEvent2 被调用, From MyDrone"));
  	return true;
  }
  

  

• 也可以蓝图重载

  

调用接口的类

• c++ 调用接口可以先判断该类是否有实现接口

  // 如果OriginalObject实现了UReactToTriggerInterface，则bisimplemated将为true。
  bool bIsImplemented = OriginalObject->GetClass()->ImplementsInterface(UReactToTriggerInterface::StaticClass()); 
  
  // 如果OriginalObject实现了UReactToTrigger，bIsImplemented将为true。
  bIsImplemented = OriginalObject->Implements<UReactToTriggerInterface>(); 
  
  // 如果OriginalObject实现了UReactToTriggerInterface，则ReactingObject将为非空。
  IReactToTriggerInterface* ReactingObject = Cast<IReactToTriggerInterface>(OriginalObject);
  

• 原生 虚函数调用按照原生C++调用即可

• UFUCNTION()修饰的接口函数则以 I接口名::Execute_函数名( 接口实例, 函数参数) 调用

代码

• MyTriggerBox.h

  #pragma once
  #include "CoreMinimal.h"
  #include "Engine/TriggerBox.h"
  #include "MyTriggerBox.generated.h"
  
  UCLASS()
  class TIPS_API AMyTriggerBox : public ATriggerBox
  {
  	GENERATED_BODY()
  
  public:
  
  	virtual void BeginPlay() override;
  
  	UFUNCTION()
  	void HandleOverlap(AActor* OverlappedActor, AActor* OtherActor );
  };
  

• MyTriggerBox.cpp

  #include "MyTriggerBox.h"
  #include "Components/BoxComponent.h"
  #include "ReactToTriggerInterface.h"
  
  void AMyTriggerBox::BeginPlay()
  {
  	//放在构造函数好像不起作用
  	OnActorBeginOverlap.AddDynamic(this, &AMyTriggerBox::HandleOverlap);
  }
  
  void AMyTriggerBox::HandleOverlap(AActor* OverlappedActor, AActor* OtherActor )
  {
  	UClass* ActorClass = OtherActor->GetClass();
  	if (ActorClass->ImplementsInterface(UReactToTriggerInterface::StaticClass()))
  	{
  		UE_LOG(LogTemp, Warning, TEXT("是否实现接口判断方法一"));
  		IReactToTriggerInterface* ReactToTriggerInterface1 = CastChecked<IReactToTriggerInterface>(OtherActor);
  
  		ReactToTriggerInterface1->ReactToTrigger_PureVirtual();
  		ReactToTriggerInterface1->ReactToTrigger_Virtual();
  
  		IReactToTriggerInterface::Execute_ReactToTrigger_NativeEvent1(OtherActor, 16);
  		IReactToTriggerInterface::Execute_ReactToTrigger_NativeEvent2(OtherActor, 32);
  		IReactToTriggerInterface::Execute_ReactToTrigger_ImplementableEvent(OtherActor);
  
  	}
  
  	if (OtherActor->Implements<UReactToTriggerInterface>())
  	{
  		UE_LOG(LogTemp, Warning, TEXT("是否实现接口判断方法二"));
  
  		IReactToTriggerInterface::Execute_ReactToTrigger_NativeEvent1(OtherActor, 16);
  		IReactToTriggerInterface::Execute_ReactToTrigger_NativeEvent2(OtherActor, 32);
  	}
  
  	IReactToTriggerInterface* ReactToTriggerInterface2 = Cast<IReactToTriggerInterface>(OtherActor);
  	if (ReactToTriggerInterface2)
  	{
  		UE_LOG(LogTemp, Warning, TEXT("是否实现接口判断方法三"));
  		IReactToTriggerInterface::Execute_ReactToTrigger_ImplementableEvent(OtherActor);
  	}
  
  }
  

测试结果

参考

• 实施蓝图接口

• 接口