目录
  1. 1. UnrealVersionSelector 的参数
  2. 2. 注册 UnrealVersionSelector
  3. 3. 获取所有已注册的引擎
  4. 4. 注册引擎
  5. 5. Launcher 版引擎注册表路径
  6. 6. 注册编译版引擎的安装路径
  7. 7. 解决.uproject 右键生成失败
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UnrealVersionSelector

UnrealVersionSelector是 UE 的一个工具，用来关联 uproject 文件、注册引擎、选择引擎版本、生成解决方案等功能的一个工具。
在对 uproject 文件点击右键时，Switch Unreal Engine Version等选项就是 UnrealVersionSelector 提供的：

UnrealVersionSelector 的参数

  • -register：Add the current directory to the list of installations
  • -fileassociations：Update all the settings.
  • -switchversion：Associate with an engine label
  • -switchversionsilent：Associate with a specific engine label
  • -editor：Open a project with the editor
  • -projectlist：Open the editor
  • -game：Play a game using the editor executable
  • -projectfiles：Generate Visual Studio project files

注册 UnrealVersionSelector

如果遇到 uproject 没有文件关联的情况可以使用下列注册表修复文件关联。

保存为.reg，双击合并即可。

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Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\.uproject]
@="Unreal.ProjectFile"

[HKEY_CLASSES_ROOT\Unreal.ProjectFile]
@="Unreal Engine Project File"

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\DefaultIcon]
@="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell]

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\open]
@="Open"

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\open\command]
@="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\" /editor \"%1\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\run]
@="Launch game"
"Icon"="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\run\command]
@="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\" /game \"%1\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\rungenproj]
@="Generate Visual Studio project files"
"Icon"="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\rungenproj\command]
@="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\" /projectfiles \"%1\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\switchversion]
@="Switch Unreal Engine version..."
"Icon"="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\""

[HKEY_CLASSES_ROOT\Unreal.ProjectFile\shell\switchversion\command]
@="\"C:\\Program Files (x86)\\Epic Games\\Launcher\\Engine\\Binaries\\Win64\\UnrealVersionSelector.exe\" /switchversion \"%1\""

获取所有已注册的引擎

可以使用 IDesktopPlatform::EnumerateEngineInstallations 来获取当前系统中所有从启动器安装、以及用户使用 UnrealVersionSelector 注册的引擎版本。

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TMap<FString,FString> Installations;
FDesktopPlatformModule::Get()->EnumerateEngineInstallations(Installations)

注册引擎

使用 UnrealVersionSelector 注册引擎时，会将注册的引擎路径写入到注册表：

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HKEY_CURRENT_USER\SOFTWARE\Epic Games\Unreal Engine\Builds

其注册表项的 lpValueName 则是生成的一个 GUID：

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// DesktopPlatfromWindows.cpp
bool FDesktopPlatformWindows::RegisterEngineInstallation(const FString &RootDir, FString &OutIdentifier)
{
  bool bRes = false;
  if(IsValidRootDirectory(RootDir))
  {
    HKEY hRootKey;
    if(RegCreateKeyEx(HKEY_CURRENT_USER, InstallationsSubKey, 0, NULL, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, NULL, &hRootKey, NULL) == ERROR_SUCCESS)
    {
      FString NewIdentifier = FGuid::NewGuid().ToString(EGuidFormats::DigitsWithHyphensInBraces);
      LRESULT SetResult = RegSetValueEx(hRootKey, *NewIdentifier, 0, REG_SZ, (const BYTE*)*RootDir, (RootDir.Len() + 1) * sizeof(TCHAR));
      RegCloseKey(hRootKey);

      if(SetResult == ERROR_SUCCESS)
      {
        OutIdentifier = NewIdentifier;
        bRes = true;
      }
    }
  }
  return bRes;
}

UE 并没有直接在 IDesktopPlatfrom 中单独提供 获取用户通过使用 UnrealVersionSelector 注册的引擎列表。
但是在 EnumerateEngineInstallations 中写了从注册表获取 per-user installations 引擎：

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void FDesktopPlatformWindows::EnumerateEngineInstallations(TMap<FString, FString> &OutInstallations)
{
  // Enumerate the binary installations
  EnumerateLauncherEngineInstallations(OutInstallations);

  // Enumerate the per-user installations
  HKEY hKey;
  if (RegOpenKeyEx(HKEY_CURRENT_USER, InstallationsSubKey, 0, KEY_ALL_ACCESS, &hKey) == ERROR_SUCCESS)
  {
    // Get a list of all the directories
    TArray<FString> UniqueDirectories;
    OutInstallations.GenerateValueArray(UniqueDirectories);

    // Enumerate all the installations
    TArray<FString> InvalidKeys;
    for (::DWORD Index = 0;; Index++)
    {
      TCHAR ValueName[256];
      TCHAR ValueData[MAX_PATH];
      ::DWORD ValueType = 0;
      ::DWORD ValueNameLength = sizeof(ValueName) / sizeof(ValueName[0]);
      ::DWORD ValueDataSize = sizeof(ValueData);

      LRESULT Result = RegEnumValue(hKey, Index, ValueName, &ValueNameLength, NULL, &ValueType, (BYTE*)&ValueData[0], &ValueDataSize);
      if(Result == ERROR_SUCCESS)
      {
        int32 ValueDataLength = ValueDataSize / sizeof(TCHAR);
        if(ValueDataLength > 0 && ValueData[ValueDataLength - 1] == 0) ValueDataLength--;

        FString NormalizedInstalledDirectory(ValueDataLength, ValueData);
        FPaths::NormalizeDirectoryName(NormalizedInstalledDirectory);
        FPaths::CollapseRelativeDirectories(NormalizedInstalledDirectory);

        if(IsValidRootDirectory(NormalizedInstalledDirectory) && !UniqueDirectories.Contains(NormalizedInstalledDirectory))
        {
          OutInstallations.Add(ValueName, NormalizedInstalledDirectory);
          UniqueDirectories.Add(NormalizedInstalledDirectory);
        }
        else
        {
          InvalidKeys.Add(ValueName);
        }
      }
      else if(Result == ERROR_NO_MORE_ITEMS)
      {
        break;
      }
    }

    // Remove all the keys which weren't valid
    for(const FString InvalidKey: InvalidKeys)
    {
      RegDeleteValue(hKey, *InvalidKey);
    }

    RegCloseKey(hKey);
  }
}

Launcher 版引擎注册表路径

上面提到，如果非源码版引擎，使用 UnrealVersionSelector 注册时会写入到注册表：

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HKEY_CURRENT_USER\SOFTWARE\Epic Games\Unreal Engine\Builds

从 EpicGameLauncher 安装的版本则会写入到另一个注册表路径下：

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HKEY_LOCAL_MACHINE\SOFTWARE\EpicGames\Unreal Engine

其值为(从注册表导出的)：

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Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\EpicGames\Unreal Engine\4.18]
"InstalledDirectory"="C:\\Program Files\\Epic Games\\UE_4.18"

UE 提供了方法来得到从 EpicGameLauncher 安装的引擎 (通过IDesktopPlatfrom 接口)：

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TMap<FString,FString> Installations;
FDesktopPlatformModule::Get()->EnumerateLauncherEngineInstallations(OutInstallations);

注册编译版引擎的安装路径

UE 提供了UnrealVersionSelector 工具用来选择引擎版本 / 生成 sln 等功能，其也可以用来注册本地的引擎 (非 Launcher 安装的引擎，如自己编译的源码版引擎) 到项目文件的右键 Select Unreal Engine Version... 列表中。
简单分析了一下 UnrealVersionSelector 的代码，它的注册流程如下：

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WinMain_Func=>start: WinMain
Main_Func=>operation: Main(Arguments)
RegisterCurrentEngineDirectoryWithPrompt_Func=>operation: RegisterCurrentEngineDirectoryWithPrompt()
RegisterCurrentEngineDirectory_Func=>operation: RegisterCurrentEngineDirectory(false)
GetEngineIdentifierFromRootDir_Func=>operation: FDesktopPlatformModule::Get()->GetEngineIdentifierFromRootDir(EngineRootDir, Identifier)
RegisterEngineInstallation_Func=>operation: RegisterEngineInstallation(RootDir, OutIdentifier)
end=>end: End

WinMain_Func->Main_Func
Main_Func->RegisterCurrentEngineDirectoryWithPrompt_Func
RegisterCurrentEngineDirectoryWithPrompt_Func->RegisterCurrentEngineDirectory_Func
RegisterCurrentEngineDirectory_Func->GetEngineIdentifierFromRootDir_Func
GetEngineIdentifierFromRootDir_Func->RegisterEngineInstallation_Func
RegisterEngineInstallation_Func->end

向注册表写入的操作在 FDesktopPlatformWindows::RegisterEngineInstallation 这个函数中。
操作为将注册的引擎目录写入到 HKEY_CURRENT_USER\Software\Epic Games\Unreal Engine\Builds 中的字符串项中。
当右键 Switch Unreal Engine Version... 的时候，会修改 .uproject 文件中的 EngineAssociation 值：

其调用流如下：

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WinMain_Func=>start: WinMain
Main_Func=>operation: Main(Arguments)
SwitchVersion_Func=>operation: SwitchVersion(const FString& ProjectFileName)
GetEngineIdentifierForProject_fUNC=>operation: FDesktopPlatformModule::Get()->GetEngineIdentifierForProject(ProjectFileName, Identifier) // 获取当前选择的引擎
SelectEngineInstallation_Func=>operation: FPlatformInstallation::SelectEngineInstallation(Identifier) // 弹出选择引擎列表框，当前选择的为默认
SetEngineIdentifierForProject_func=>operation: FDesktopPlatformModule::Get()->SetEngineIdentifierForProject(ProjectFileName, Identifier) // 设置选择的引擎，并写入 uproject 文件
ContentOnly=>condition: Is Content Only Project?
GenerateProjectFiles_func=>operation: GenerateProjectFiles(ProjectFileName)
end=>end: End


WinMain_Func->Main_Func
Main_Func->SwitchVersion_Func
SwitchVersion_Func->GetEngineIdentifierForProject_fUNC
GetEngineIdentifierForProject_fUNC->SelectEngineInstallation_Func
SelectEngineInstallation_Func->SetEngineIdentifierForProject_func
SetEngineIdentifierForProject_func->ContentOnly
ContentOnly(yes)->end
ContentOnly(no)->GenerateProjectFiles_func
GenerateProjectFiles_func->end

执行项目文件写入的操作在 FDesktopPlatformBase::SetEngineIdentifierForProject 中：

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bool FDesktopPlatformBase::SetEngineIdentifierForProject(const FString &ProjectFileName, const FString &InIdentifier)
{
  // Load the project file
  TSharedPtr<FJsonObject> ProjectFile = LoadProjectFile(ProjectFileName);
  if (!ProjectFile.IsValid())
  {
    return false;
  }

  // Check if the project is a non-foreign project of the given engine installation. If so, blank the identifier 
  // string to allow portability between source control databases. GetEngineIdentifierForProject will translate
  // the association back into a local identifier on other machines or syncs.
  FString Identifier = InIdentifier;
  if(Identifier.Len() > 0)
  {
    FString RootDir;
    if(GetEngineRootDirFromIdentifier(Identifier, RootDir))
    {
      const FUProjectDictionary &Dictionary = GetCachedProjectDictionary(RootDir);
      if(!Dictionary.IsForeignProject(ProjectFileName))
      {
        Identifier.Empty();
      }
    }
  }

  // Set the association on the project and save it
  ProjectFile->SetStringField(TEXT("EngineAssociation"), Identifier);
  return SaveProjectFile(ProjectFileName, ProjectFile);
}

所以如果你选择了一个项目使用编译版引擎，可以使用文本编辑器打开该项目的 .uproject 文件，可以看到其中的 EngineAssociation 项的值就是注册表中的引擎版本值。

注：UnrealVersionSelector所支持的命令行参数及其用途在UnrealVersionSelector.cpp#L224:

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int Main(const TArray<FString>& Arguments)
{
  bool bRes = false;
  if (Arguments.Num() == 0)
  {
    // Add the current directory to the list of installations
    bRes = RegisterCurrentEngineDirectoryWithPrompt();
  }
  else if (Arguments.Num() == 1 && Arguments[0] == TEXT("-register"))
  {
    // Add the current directory to the list of installations
    bRes = RegisterCurrentEngineDirectory(true);
  }
  else if (Arguments.Num() == 1 && Arguments[0] == TEXT("-fileassociations"))
  {
    // Update all the settings.
    bRes = UpdateFileAssociations();
  }
  else if (Arguments.Num() == 2 && Arguments[0] == TEXT("-switchversion"))
  {
    // Associate with an engine label
    bRes = SwitchVersion(Arguments[1]);
  }
  else if (Arguments.Num() == 3 && Arguments[0] == TEXT("-switchversionsilent"))
  {
    // Associate with a specific engine label
    bRes = SwitchVersionSilent(Arguments[1], Arguments[2]);
  }
  else if (Arguments.Num() == 2 && Arguments[0] == TEXT("-editor"))
  {
    // Open a project with the editor
    bRes = LaunchEditor(Arguments[1], L"");
  }
  else if (Arguments.Num() == 2 && Arguments[0] == TEXT("-game"))
  {
    // Play a game using the editor executable
    bRes = LaunchEditor(Arguments[1], L"-game");
  }
  else if (Arguments.Num() == 2 && Arguments[0] == TEXT("-projectfiles"))
  {
    // Generate Visual Studio project files
    bRes = GenerateProjectFiles(Arguments[1]);
  }
  else
  {
    // Invalid command line
    FPlatformMisc::MessageBoxExt(EAppMsgType::Ok, TEXT("Invalid command line"), NULL);
  }
  return bRes ? 0 : 1;
}

解决.uproject 右键生成失败

首先要查看右键菜单所使用的 UnrealVersionSelector.exe 的路径，可以打开注册表:

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HKEY_CLASSES_ROOT\Unreal.ProjectFile

然后找到 shell\open\command 条目查看 UnrealVersionSelector.exe 的位置(如果没有安装过源码版引擎则默认在 EpicGamesLauncher 的 Binaries 路径下)，如：

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"C:\Program Files (x86)\Epic Games\Launcher\Engine\Binaries\Win64\UnrealVersionSelector.exe" /editor "%1"

然后打开 C:\Program Files (x86)\Epic Games\Launcher\Engine\Binaries\Win64，将UnrealVersionSelector.exe 设置为以管理员权限启动即可(右键 - 属性 - 兼容性 - 以管理员身份运行此程序)。