如何使用 UE4 C++ 中的参数将 UFunction 添加到接口的委托？

Question

I am looking use web sockets in Unreal. I am following the tutorial found here: Web Socket Tutorial

Most notably I am trying to bind to the events before connection. In the example, they use .AddLambda however, I would like to try to use .AddUFunction . It seems the function takes in the Object, the function name, and VarTypes...types . I can't seem to figure out what the last parameter is for the delegates that use parameters. (At least I believe that is the problem anyway) The functions themselves have the correct signature and matches the delegates I want to bind to.

Here is what I have so far:

void AWebSocketController::CreateWebSocket(FString ServerUrl, FString ServerProtocol)
{
  Socket = FWebSocketsModule::Get().CreateWebSocket(ServerUrl, ServerProtocol);

  // We bind to the events
  Socket->OnConnected().AddUFunction(this, FName("OnSocketConnection"));

  Socket->OnConnectionError().AddUFunction(this, FName("OnSocketConnectionError"));

  Socket->OnClosed().AddUFunction(this, FName("OnSocketClosed"));

  Socket->OnMessage().AddUFunction(this, FName("OnSocketReceiveMessage"));

  Socket->OnMessageSent().AddUFunction(this, FName("OnSocketSentMessage"));

  // And we finally connect to the server. 
  Socket->Connect();

}

It gives me the following error messages:

error LNK2005: "public: void __cdecl AWebSocketController::OnSocketClosed(int,class FString const &,bool)" (?OnSocketClosed@AWebSocketController@@QEAAXHAEBVFString@@_N@Z) already defined in WebSocketController.cpp.obj
error LNK2005: "public: void __cdecl AWebSocketController::OnSocketConnection(void)" (?OnSocketConnection@AWebSocketController@@QEAAXXZ) already defined in WebSocketController.cpp.obj
error LNK2005: "public: void __cdecl AWebSocketController::OnSocketConnectionError(class FString const &)" (?OnSocketConnectionError@AWebSocketController@@QEAAXAEBVFString@@@Z) already defined in WebSocketController.cpp.obj
error LNK2005: "public: void __cdecl AWebSocketController::OnSocketReceiveMessage(class FString const &)" (?OnSocketReceiveMessage@AWebSocketController@@QEAAXAEBVFString@@@Z) already defined in WebSocketController.cpp.obj
error LNK2005: "public: void __cdecl AWebSocketController::OnSocketSentMessage(class FString const &)" (?OnSocketSentMessage@AWebSocketController@@QEAAXAEBVFString@@@Z) already defined in WebSocketController.cpp.obj

The function definitions:

void AWebSocketController::OnSocketConnection()
{
}

void AWebSocketController::OnSocketConnectionError(const FString& ErrorMessage)
{
}

void AWebSocketController::OnSocketClosed(int32 StatusCode, const FString& Reason, bool WasClean)
{
}

void AWebSocketController::OnSocketReceiveMessage(const FString& Message)
{
}

void AWebSocketController::OnSocketSentMessage(const FString& Message)
{
}

I have never come across this .AddUFunction before and I can't seem to find any examples of how to use it. If anyone can help me out or point me in the right direction, it would be appreciated.

Answer 1

Please read the Documentation on Events

You must declare function signatures that match that of the Event Delegate within your class for which a function pointer will be bound.

The example image above is from the Engine Source.

Answer 2

Works for me!

SandboxGameInstance.cpp

#include "SandboxGameInstance.h"

#include "WebSocketsModule.h"
#include "IWebSocket.h"       // Socket definition
void USandboxGameInstance::Init()
{
    Super::Init();
    FWebSocketsModule& Module = FModuleManager::LoadModuleChecked<FWebSocketsModule>(TEXT("WebSockets"));

    const FString ServerURL = TEXT("ws://127.0.0.1:3000/"); // Your server URL. You can use ws, wss or wss+insecure.
    const FString ServerProtocol = TEXT("ws");              // The WebServer protocol you want to use.

    TSharedPtr<IWebSocket> Socket = FWebSocketsModule::Get().CreateWebSocket(ServerURL, ServerProtocol);

    // We bind to the events
    Socket->OnConnected().AddUFunction(this, FName("OnSocketConnection"));

    Socket->OnConnectionError().AddUFunction(this, FName("OnSocketConnectionError"));

    Socket->OnClosed().AddUFunction(this, FName("OnSocketClosed"));

    Socket->OnMessage().AddUFunction(this, FName("OnSocketReceiveMessage"));

    Socket->OnMessageSent().AddUFunction(this, FName("OnSocketSentMessage"));

    // And we finally connect to the server. 
    Socket->Connect();
}

void USandboxGameInstance::OnSocketConnection()
{
    UE_LOG(LogTemp, Warning, TEXT("CONNECTED"));
}

void USandboxGameInstance::OnSocketConnectionError(const FString& ErrorMessage)
{
    UE_LOG(LogTemp, Warning, TEXT("ERROR"));
}

void USandboxGameInstance::OnSocketClosed(int32 StatusCode, const FString& Reason, bool WasClean)
{
    UE_LOG(LogTemp, Warning, TEXT("CLOSED"));
}

void USandboxGameInstance::OnSocketReceiveMessage(const FString& Message)
{
    UE_LOG(LogTemp, Warning, TEXT("RECEIVED"));
}

void USandboxGameInstance::OnSocketSentMessage(const FString& Message)
{
    UE_LOG(LogTemp, Warning, TEXT("SENT"));
}

SandboxGameInstance.h

#pragma once

#include "CoreMinimal.h"
#include "Engine/GameInstance.h"
#include "SandboxGameInstance.generated.h"

UCLASS()
class SANDBOX_API USandboxGameInstance : public UGameInstance
{
    GENERATED_BODY()
public:
    virtual void Init() override;

    UFUNCTION()
    void OnSocketConnection();

    UFUNCTION()
    void OnSocketConnectionError(const FString& ErrorMessage);

    UFUNCTION()
    void OnSocketClosed(int32 StatusCode, const FString& Reason, bool WasClean);

    UFUNCTION()
    void OnSocketReceiveMessage(const FString& Message);

    UFUNCTION()
    void OnSocketSentMessage(const FString& Message);
};