UE4中类自动生成代码解析

本文章由cartzhang编写，转载请注明出处。所有权利保留。

文章链接：http://blog.csdn.net/cartzhang/article/details/73189272

作者：cartzhang

一、 UE4 C++ 代码自动生成流程

1. 界面点击生成C++类

图1

先调用 SMenuEntryBlock::OnClicked ，然后调用UI_COMMAND(AddCodeToProject) —-> FMainFrameActionCallbacks::AddCodeToProject()，—-> OpenAddCodeToProjectDialog来打开基类选择界面。

2. 点击Create Class按钮

图2

OnFinished(this, &SNewClassDialog::FinishClicked)

调用函数SNewClassDialog::FinishClicked()—>AddCodeToProject —>GameProjectUtils::AddCodeToProject_Internal(核心都在这里实现)

3. 头文件生成

拼接文件路径信息，GameProjectUtils::GenerateClassHeaderFile来生成头文件的内容。

FinalOutput = "
// Fill out your copyright notice in the Description page of Project Settings.
#pragma once
#include "GameFramework/Pawn.h"
#include "MyPawn.generated.h"
UCLASS()
class HOWTO_VTE_API AMyPawn : public APawn
{
    GENERATED_BODY()
public:
    // Sets default values for this pawn's properties
    AMyPawn();
protected:
    // Called when the game starts or when spawned
    virtual void BeginPlay() override;
public:
    // Called every frame
    virtual void Tick(float DeltaTime) override;
    // Called to bind functionality to input
    virtual void SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent) override;
};
"

4. 生成CPP文件

GenerateClassCPPFile

CPP = // Fill out your copyright notice in the Description page of Project Settings.
#include "HowTo_VTE.h"
#include "MyPawn.h"
// Sets default values
AMyPawn::AMyPawn()
{
    // Set this pawn to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
    PrimaryActorTick.bCanEverTick = true;
}
// Called when the game starts or when spawned
void AMyPawn::BeginPlay()
{
    Super::BeginPlay();
    %CURSORFOCUSLOCATION%
}
// Called every frame
void AMyPawn::Tick(float DeltaTime)
{
    Super::Tick(DeltaTime);
}
// Called to bind functionality to input
void AMyPawn::SetupPlayerInputComponent(UInputComponent* PlayerInputComponent)
{
    Super::SetupPlayerInputComponent(PlayerInputComponent);
}

5. 编译

检测是否可避免全部编译工程，自动热加载，代码首次编译，RecompileModule —>

CheckForFinishedModuleDLLCompile

图3

6. 工程重新加载。

代码生成完毕。

二、一张图

图4

一图千言

三、文件生成模板

UE4 代码写的很精妙！

看模板头文件生成：

FString FinalOutput = Template.Replace(TEXT("%COPYRIGHT_LINE%"), *MakeCopyrightLine(), ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%UNPREFIXED_CLASS_NAME%"), *UnPrefixedClassName, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%CLASS_MODULE_API_MACRO%"), *ModuleAPIMacro, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%UCLASS_SPECIFIER_LIST%"), *MakeCommaDelimitedList(ClassSpecifierList, false), ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%PREFIXED_CLASS_NAME%"), *PrefixedClassName, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%PREFIXED_BASE_CLASS_NAME%"), *PrefixedBaseClassName, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%EVENTUAL_CONSTRUCTOR_DECLARATION%"), *EventualConstructorDeclaration, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%CLASS_PROPERTIES%"), *ClassProperties, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%CLASS_FUNCTION_DECLARATIONS%"), *ClassFunctionDeclarations, ESearchCase::CaseSensitive);
    FinalOutput = FinalOutput.Replace(TEXT("%BASE_CLASS_INCLUDE_DIRECTIVE%"), *BaseClassIncludeDirective, ESearchCase::CaseSensitive);

CPP文件也类似的。

其中，Tmplate得到是某个继承类的模板字符串，然后通过特定符号来进行替换，生成文件。

模板文件的路径在：UE4_source\UnrealEngine\Engine\Content\Editor\Templates\

比如测试的继承基类为Pawn，他们的模板头文件和CPP文件分别为： PawnClass.h.template 和PawnClass.cpp.template 。

可以自行打开和修改文件。

PawnClass.h.template

%COPYRIGHT_LINE%
#pragma once
%BASE_CLASS_INCLUDE_DIRECTIVE%
#include "%UNPREFIXED_CLASS_NAME%.generated.h"
UCLASS(%UCLASS_SPECIFIER_LIST%)
class %CLASS_MODULE_API_MACRO%%PREFIXED_CLASS_NAME% : public %PREFIXED_BASE_CLASS_NAME%
{
    GENERATED_BODY()
public:
    // Sets default values for this pawn's properties
    %PREFIXED_CLASS_NAME%();
protected:
    // Called when the game starts or when spawned
    virtual void BeginPlay() override;
public:
    // Called every frame
    virtual void Tick(float DeltaTime) override;
    // Called to bind functionality to input
    virtual void SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent) override;
    %CLASS_FUNCTION_DECLARATIONS%
    %CLASS_PROPERTIES%
};

PawnClass.cpp.template

%COPYRIGHT_LINE%
#include "%MODULE_INCLUDE_PATH%"
#include "%UNPREFIXED_CLASS_NAME%.h"
%ADDITIONAL_INCLUDE_DIRECTIVES%
// Sets default values
%PREFIXED_CLASS_NAME%::%PREFIXED_CLASS_NAME%()
{
    // Set this pawn to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
    PrimaryActorTick.bCanEverTick = true;
}
// Called when the game starts or when spawned
void %PREFIXED_CLASS_NAME%::BeginPlay()
{
    Super::BeginPlay();
    %CURSORFOCUSLOCATION%
}
// Called every frame
void %PREFIXED_CLASS_NAME%::Tick(float DeltaTime)
{
    Super::Tick(DeltaTime);
}
// Called to bind functionality to input
void %PREFIXED_CLASS_NAME%::SetupPlayerInputComponent(UInputComponent* PlayerInputComponent)
{
    Super::SetupPlayerInputComponent(PlayerInputComponent);
}
%ADDITIONAL_MEMBER_DEFINITIONS%

是不是可以自定义头文件呢，估计可以。暂时没有研究。

UE4 工程量太大了，什么样脑子才能架构这玩意啊，他们都是天才！

UE4Paragon游戏人物截图！

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