Unreal Engine 4 学习笔记（十二）：Plugins

如何使代码模块化，使用Plugins可能是一种比较好的方式，下面通过一个例子，讲一讲如何创建和使用Plugins。

一、创建C++工程TestPlugins:

从菜单中选择"Edit"->"Plugins"，会弹出如下窗口：

点出“New Plgin”，在弹出的窗口中选中“Blank”，然后输入“Shape”，点出“Create Plugin”后，会创建一个名为“Shape”的plugin：

工程的目录结构如下：

从上图可以看到，Shape Plugin的代码目录和TestPlugin工程的基本上是一样的，都有Source文件夹和.uproject文件，Source文件夹下都有.Build.cs文件。打开“Shape.Build.cs”文件，可以看到内容如下：

// Copyright 1998-2017 Epic Games, Inc. All Rights Reserved.

using UnrealBuildTool;

public class Shape : ModuleRules
{
	public Shape(ReadOnlyTargetRules Target) : base(Target)
	{
		PCHUsage = ModuleRules.PCHUsageMode.UseExplicitOrSharedPCHs;
		
		PublicIncludePaths.AddRange(
			new string[] {
				"Shape/Public"
				// ... add public include paths required here ...
			}
			);
				
		
		PrivateIncludePaths.AddRange(
			new string[] {
				"Shape/Private",
				// ... add other private include paths required here ...
			}
			);
			
		
		PublicDependencyModuleNames.AddRange(
			new string[]
			{
				"Core",
				// ... add other public dependencies that you statically link with here ...
			}
			);
			
		
		PrivateDependencyModuleNames.AddRange(
			new string[]
			{
				"CoreUObject",
				"Engine",
				"Slate",
				"SlateCore",
				// ... add private dependencies that you statically link with here ...	
			}
			);
		
		
		DynamicallyLoadedModuleNames.AddRange(
			new string[]
			{
				// ... add any modules that your module loads dynamically here ...
			}
			);
	}
}

内容和TestPlugin.Build.cs大致相同，主要是多了对“Public”和“Private”这两个目录的包含，实际上TestPlugin也可以创建这两个目录来存放代码，只要在TestPlugin.Build.cs中中加入如下代码即可：

PublicIncludePaths.AddRange(
	new string[] {
		"TestPlugin/Public"
		// ... add public include paths required here ...
	}
	);
		

PrivateIncludePaths.AddRange(
	new string[] {
		"TestPlugin/Private",
		// ... add other private include paths required here ...
	}
	);

二、在Shape中添加代码：

代码目录结构：

Shape--+
       |-Public--+
       |         |-circle.h
       |
       |-Private-+
                 |-circle_impl.h
                 |-circle_impl.cpp
                 |-circle.cpp

// circle.h
// 圆的接口类
class SHAPE_API Circle {
public:
	virtual ~Circle() {};

	// 接口方法：面积
	virtual double area() = 0;


	static Circle* create(double radius);     // 创建circle实例
	static void destroy(Circle* circlePtr);   // 销毁circle实例
};

// circle.cpp
#include "circle.h"
#include "circle_impl.h"

Circle* Circle::create(double radius) {
	Circle* circlePtr = new CircleImpl(radius);

	return circlePtr;
};

void Circle::destroy(Circle* circlePtr) {
	delete circlePtr;
};

// circle_impl.h
#include "circle.h"

// 圆的具体实现类
class CircleImpl : public Circle {

private:
	double radius;
public:
	CircleImpl(double radius);
	double area() override;
};

// circle_impl.cpp
#include "circle_impl.h"

#include <cmath>

inline double pi() {
	return std::atan(1) * 4;
};

CircleImpl::CircleImpl(double _radius) : radius(_radius) {
};

double CircleImpl::area() {
	return pi() * radius * radius;
};

中宏SHAPE_API会自动被识别，用于把Plugin导出成dll，可能的名字为UE4Editor-Shape.dll。

三、 修改TestPlugin工程

在“TestPlugin.Build.cs”中添加“Shape”Plugin，否则编译时会找不到。

PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "Shape" });

修改ATestPluginGameModeBase：

// TestPluginGameModeBase.h
#pragma once

#include "CoreMinimal.h"
#include "GameFramework/GameModeBase.h"

#include "circle.h"

#include "TestPluginGameModeBase.generated.h"

/**
 * 
 */
UCLASS()
class TESTPLUGIN_API ATestPluginGameModeBase : public AGameModeBase
{
	GENERATED_BODY()

private:
	Circle* circle;
	
public:

	ATestPluginGameModeBase();

	~ATestPluginGameModeBase();
	
	void BeginPlay();
};

// TestPluginGameModeBase.cpp

#include "TestPluginGameModeBase.h"


ATestPluginGameModeBase::ATestPluginGameModeBase() {

	circle = Circle::create(10);

	UE_LOG(LogTemp, Log, TEXT("circle.area=%f"), circle->area());
};

ATestPluginGameModeBase::~ATestPluginGameModeBase() {
};


void ATestPluginGameModeBase::BeginPlay() {
	Circle::destroy(circle);

	UE_LOG(LogTemp, Log, TEXT("destroy circle"));
};

同时在UEEditor将当前Level的GameMode设置成TestPluginGameModeBase：

编译后，点Play，就可以在Output Log中看到打印的日志了。

参考文档：

https://docs.unrealengine.com/en-us/Programming/Plugins

https://wiki.unrealengine.com/An_Introduction_to_UE4_Plugins