【UE4 C++ 基礎知識】<9> Interface 接口

概述

• 簡單的說，接口提供一組公共的方法，不同的對象中繼承這些方法后可以有不同的具體實現。
• 任何使用接口的類都必須實現這些接口。
• 實現解耦
• 解決多繼承的問題

藍圖使用

使用方法

三種調用方法的區別

調用流關卡藍圖的接口函數

C++ 使用接口

本例使用一個Box Trigger 出發overlap 調用 Drone實例的接口

添加接口類

定義接口

聲明藍圖可調用接口函數

• 用UFUNCTION 宏 BlueprintCallable 聲明藍圖可調用，還必須使用 BlueprintImplementableEvent 或 BlueprintNativeEvent 說明，而且函數不能為虛函數

• 如果不想藍圖重載，只是想使用 BlueprintCallable 以支持藍圖起到單純的調用作用，可以通過將接口標記為 UINTERFACE(meta = (CannotImplementInterfaceInBlueprint)) 來解決

• 通過聲明 virtual 虛函數，使得派生類可重載

代碼

• ReactToTriggerInterface.h

  #pragma once
  #include "CoreMinimal.h"
  #include "UObject/Interface.h"
  #include "ReactToTriggerInterface.generated.h"
  
  // 無需更改
  // UINTERFACE類不是實際的接口；它是一個空白類，它的存在只是為了向虛幻引擎反射系統確保可見性。
  UINTERFACE(MinimalAPI)
  class UReactToTriggerInterface : public UInterface
  {
  	GENERATED_BODY()
  };
  
  //開頭字母"U"必須改為"I"。
  class TIPS_API IReactToTriggerInterface
  {
  	GENERATED_BODY()
  
  public:
  
  	// 純虛函數，實現類必須實現接口
  	virtual void ReactToTrigger_PureVirtual() = 0;
  
  	// 虛函數，在接口本身的 .h 或 .cpp 文件中提供默認實現.實現類可覆蓋
  	virtual void ReactToTrigger_Virtual();
  
  	//實現類可以在藍圖和C++中實現接口
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category="Trigger Reaction")
  		void ReactToTrigger_NativeEvent1(int32 number);
  
  	//實現類可以在藍圖和C++中實現接口
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category = "Trigger Reaction")
  		bool ReactToTrigger_NativeEvent2(int32 number);
  
  	//實現類在藍圖中實現接口
  	UFUNCTION(BlueprintCallable, BlueprintImplementableEvent, Category = "Trigger Reaction")
  		void ReactToTrigger_ImplementableEvent();
  };
  

• ReactToTriggerInterface.cpp

  #include "ReactToTriggerInterface.h"
  void IReactToTriggerInterface::ReactToTrigger_Virtual()
  {
  	// unimplemented(); //該宏將在執行代碼行時發出調試語句, 中斷
  	UE_LOG(LogTemp, Warning, TEXT("ReactToTrigger_Virtual 被調用, From 接口本身"));
  }
  

實現接口

• MyDrone.h 此類繼承自Pawn類，無關本文主題

  #include "ReactToTriggerInterface.h"
  #include "MyDrone.generated.h"
  
  UCLASS()
  class TIPS_API AMyDrone : public ADrone, public IReactToTriggerInterface
  {
  	GENERATED_BODY()
  
  public:
  	virtual void ReactToTrigger_PureVirtual() override;
  
  	//可藍圖調用，貌似通用寫法
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category = "Trigger Reaction")
  		void ReactToTrigger_NativeEvent1(int32 number);
  		virtual void ReactToTrigger_NativeEvent1_Implementation(int32 number) override;
  
  	//藍圖可調用,,貌似和上面沒區別
  	virtual bool ReactToTrigger_NativeEvent2_Implementation(int32 number) override;
  
  	//void ReactToTrigger_ImplementableEvent();需要在藍圖實現	
  };
  

• MyDrone.cpp

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

  

• 也可以藍圖重載

  

調用接口的類

• c++ 調用接口可以先判斷該類是否有實現接口

  // 如果OriginalObject實現了UReactToTriggerInterface，則bisimplemated將為true。
  bool bIsImplemented = OriginalObject->GetClass()->ImplementsInterface(UReactToTriggerInterface::StaticClass()); 
  
  // 如果OriginalObject實現了UReactToTrigger，bIsImplemented將為true。
  bIsImplemented = OriginalObject->Implements<UReactToTriggerInterface>(); 
  
  // 如果OriginalObject實現了UReactToTriggerInterface，則ReactingObject將為非空。
  IReactToTriggerInterface* ReactingObject = Cast<IReactToTriggerInterface>(OriginalObject); 
  

• 原生 虛函數調用按照原生C++調用即可

• UFUCNTION()修飾的接口函數則以 I接口名::Execute_函數名( 接口實例, 函數參數) 調用

代碼

• 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()
  {
  	//放在構造函數好像不起作用
  	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("是否實現接口判斷方法一"));
  		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("是否實現接口判斷方法二"));
  
  		IReactToTriggerInterface::Execute_ReactToTrigger_NativeEvent1(OtherActor, 16);
  		IReactToTriggerInterface::Execute_ReactToTrigger_NativeEvent2(OtherActor, 32);
  	}
  
  	IReactToTriggerInterface* ReactToTriggerInterface2 = Cast<IReactToTriggerInterface>(OtherActor);
  	if (ReactToTriggerInterface2)
  	{
  		UE_LOG(LogTemp, Warning, TEXT("是否實現接口判斷方法三"));
  		IReactToTriggerInterface::Execute_ReactToTrigger_ImplementableEvent(OtherActor);
  	}
  
  }
  

測試結果

參考

• 實施藍圖接口

• 接口