移动端指定启动参数

UE4 打出来的 Windows 包可以使用 XXXX.exe -Params 等方式来传递给游戏参数，但是移动平台 (IOS/Android) 打包出来的怎么传递参数呢？

Android 启动参数

看了一下引擎里的代码，在 Launch 模块下 Launch\Private\Android\LaunchAndroid.cpp 中有 InitCommandLine 函数：

// Launch\Private\Android\LaunchAndroid.cpp
static void InitCommandLine()
{
  static const uint32 CMD_LINE_MAX = 16384u;

  // initialize the command line to an empty string
  FCommandLine::Set(TEXT(""));

  AAssetManager* AssetMgr = AndroidThunkCpp_GetAssetManager();
  AAsset* asset = AAssetManager_open(AssetMgr, TCHAR_TO_UTF8(TEXT("UE4CommandLine.txt")), AASSET_MODE_BUFFER);
  if (nullptr != asset)
  {
    const void* FileContents = AAsset_getBuffer(asset);
    int32 FileLength = AAsset_getLength(asset);

    char CommandLine[CMD_LINE_MAX];
    FileLength = (FileLength < CMD_LINE_MAX - 1) ? FileLength : CMD_LINE_MAX - 1;
    memcpy(CommandLine, FileContents, FileLength);
    CommandLine[FileLength] = '\0';

    AAsset_close(asset);

    // chop off trailing spaces
    while (*CommandLine && isspace(CommandLine[strlen(CommandLine) - 1]))
    {
      CommandLine[strlen(CommandLine) - 1] = 0;
    }

    FCommandLine::Append(UTF8_TO_TCHAR(CommandLine));
    FPlatformMisc::LowLevelOutputDebugStringf(TEXT("APK Commandline: %s"), FCommandLine::Get());
  }

  // read in the command line text file from the sdcard if it exists
  FString CommandLineFilePath = GFilePathBase + FString("/UE4Game/") + (!FApp::IsProjectNameEmpty() ? FApp::GetProjectName() : FPlatformProcess::ExecutableName()) + FString("/UE4CommandLine.txt");
  FILE* CommandLineFile = fopen(TCHAR_TO_UTF8(*CommandLineFilePath), "r");
  if(CommandLineFile == NULL)
  {
    // if that failed, try the lowercase version
    CommandLineFilePath = CommandLineFilePath.Replace(TEXT("UE4CommandLine.txt"), TEXT("ue4commandline.txt"));
    CommandLineFile = fopen(TCHAR_TO_UTF8(*CommandLineFilePath), "r");
  }

  if(CommandLineFile)
  {
    char CommandLine[CMD_LINE_MAX];
    fgets(CommandLine, ARRAY_COUNT(CommandLine) - 1, CommandLineFile);

    fclose(CommandLineFile);

    // chop off trailing spaces
    while (*CommandLine && isspace(CommandLine[strlen(CommandLine) - 1]))
    {
      CommandLine[strlen(CommandLine) - 1] = 0;
    }

    // initialize the command line to an empty string
    FCommandLine::Set(TEXT(""));

    FCommandLine::Append(UTF8_TO_TCHAR(CommandLine));
    FPlatformMisc::LowLevelOutputDebugStringf(TEXT("Override Commandline: %s"), FCommandLine::Get());
  }

#if !UE_BUILD_SHIPPING
  if (FString* ConfigRulesCmdLineAppend = FAndroidMisc::GetConfigRulesVariable(TEXT("cmdline")))
  {
    FCommandLine::Append(**ConfigRulesCmdLineAppend);
    FPlatformMisc::LowLevelOutputDebugStringf(TEXT("ConfigRules appended: %s"), **ConfigRulesCmdLineAppend);
  }
#endif
}

简单来说就是在 UE4Game/ProjectName/ue4commandline.txt 中把启动参数写到里面，引擎启动的时候会从这个文件去读，然后添加到 FCommandLine 中。

IOS 启动参数

与 Android 的做法相同，IOS 的参数传递是在 main 函数中调用FIOSCommandLineHelper::InitCommandArgs(FString());，不过路径和 Android 不一样：

static void InitCommandArgs(FString AdditionalCommandArgs)
{
  // initialize the commandline
  FCommandLine::Set(TEXT(""));

  FString CommandLineFilePath = FString([[NSBundle mainBundle] bundlePath]) + TEXT("/ue4commandline.txt");

  // read in the command line text file (coming from UnrealFrontend) if it exists
  FILE* CommandLineFile = fopen(TCHAR_TO_UTF8(*CommandLineFilePath), "r");
  if(CommandLineFile)
  {
    FPlatformMisc::LowLevelOutputDebugStringf(TEXT("Found ue4commandline.txt file") LINE_TERMINATOR);

    char CommandLine[CMD_LINE_MAX] = {0};
    char* DataExists = fgets(CommandLine, ARRAY_COUNT(CommandLine) - 1, CommandLineFile);
    if (DataExists)
    {
      // chop off trailing spaces
      while (*CommandLine && isspace(CommandLine[strlen(CommandLine) - 1]))
      {
        CommandLine[strlen(CommandLine) - 1] = 0;
      }

      FCommandLine::Append(UTF8_TO_TCHAR(CommandLine));
    }
  }
  else
  {
    FPlatformMisc::LowLevelOutputDebugStringf(TEXT("No ue4commandline.txt [%s] found") LINE_TERMINATOR, *CommandLineFilePath);
  }

  if (!AdditionalCommandArgs.IsEmpty() && !FChar::IsWhitespace(AdditionalCommandArgs[0]))
  {
    FCommandLine::Append(TEXT(" "));
  }
  FCommandLine::Append(*AdditionalCommandArgs);

  // now merge the GSavedCommandLine with the rest
  FCommandLine::Append(*GSavedCommandLine);

  FPlatformMisc::LowLevelOutputDebugStringf(TEXT("Combined iOS Commandline: %s") LINE_TERMINATOR, FCommandLine::Get());
}

关键就是 [[NSBundle mainBundle] bundlePath] 这一句，它获取的是 App 的包路径，所以把 UE4CommandLine.txt 放到包路径下就可以了，可以使用 iMaZing 或者爱思助手之类的工具访问 App 的数据目录，放入 ue4commandline.txt 即可。

• NSBundle