目录
  1. 1. Android 运行时请求权限
  2. 2. Android 获取包名
  3. 3. Android 获取外部存储路径
  4. 4. Android 获取已安装 App 的 Apk 路径
  5. 5. 升级至 AndroidX 资料
  6. 6. 为 APK 添加外部存储读写权限
  7. 7. AndroidP HTTP 请求错误
  8. 8. Android 写入文件
  9. 9. Android 写入文件错误码对照
  10. 10. UE 项目启动参数
  11. 11. Android 设置宽高比
MobileAndroid
,
UE4.25
lipengzha
New
Edit

UE 开发 Android 的工程实践

Android 运行时请求权限

ActivityCompact 里面有个 requestPermission 方法，可以用来处理这种情况。

Android 获取包名

通过 UPL 在 Java 里添加以下代码：

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public String AndroidThunkJava_GetPackageName()
{
  Context context = getApplicationContext();
  return context.getPackageName();
}

在 C++ 里通过 JNI 调用即可：

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FString UFlibAppHelper::GetAppPackageName()
{
    FString result;
#if PLATFORM_ANDROID
    if (JNIEnv* Env = FAndroidApplication::GetJavaEnv())
    {
        jmethodID GetInstalledPakPathMethodID = FJavaWrapper::FindMethod(Env, FJavaWrapper::GameActivityClassID, "AndroidThunkJava_GetPackageName", "()Ljava/lang/String;", false);
        result = FJavaHelper::FStringFromLocalRef(Env, (jstring)FJavaWrapper::CallObjectMethod(Env, FJavaWrapper::GameActivityThis,GetInstalledPakPathMethodID));
    }
#endif
    return result; 
}

Android 获取外部存储路径

获取 App 的沙盒路径：

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// /storage/emulated/0/Android/data/com.xxxx.yyyy.zzzz/files
FString FAndroidGCloudPlatformMisc::getExternalStorageDirectory()
{
    FString result;
    if (JNIEnv* Env = FAndroidApplication::GetJavaEnv())
    {
        // get context
        jobject JniEnvContext;
        {
            jclass activityThreadClass = Env->FindClass("android/app/ActivityThread");
            jmethodID currentActivityThread = FJavaWrapper::FindStaticMethod(Env, activityThreadClass, "currentActivityThread", "()Landroid/app/ActivityThread;", false);
            jobject at = Env->CallStaticObjectMethod(activityThreadClass, currentActivityThread);
            jmethodID getApplication = FJavaWrapper::FindMethod(Env, activityThreadClass, "getApplication", "()Landroid/app/Application;", false);

            JniEnvContext = FJavaWrapper::CallObjectMethod(Env, at, getApplication);
        }
        jmethodID getExternalFilesDir = Env->GetMethodID(Env->GetObjectClass(JniEnvContext), "getExternalFilesDir", "(Ljava/lang/String;)Ljava/io/File;");
        // get File
        jobject ExternalFileDir = Env->CallObjectMethod(JniEnvContext, getExternalFilesDir,nullptr);
        // getPath method in File class
        jmethodID getFilePath = Env->GetMethodID(Env->FindClass("java/io/File"), "getPath", "()Ljava/lang/String;");
        jstring pathString = (jstring)Env->CallObjectMethod(ExternalFileDir, getFilePath, nullptr);
        const char *nativePathString = Env->GetStringUTFChars(pathString, 0);
        result = ANSI_TO_TCHAR(nativePathString);
    }
    return result;
}

Android 获取已安装 App 的 Apk 路径

有个需求，需要在运行时获取到，App 的 Apk 路径，查了一下 UE 里没有现成的接口，只能用 JNI 调用从 Java 那边想办法了。
通过在 Android Developer 上查找，发现 ApplicationInfo 中具有 sourceDir 属性，记录着 APK 的路径。
而可以通过 PackageManager 调用 getApplicationInfo 可以获取指定包名的 ApplicationInfo。

那么就好说了，UPL 里 java 代码走起：

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public String AndroidThunkJava_GetInstalledApkPath()
{
    Context context = getApplicationContext();
    PackageManager packageManager = context.getPackageManager();
    ApplicationInfo appInfo;
    try{
        appInfo = packageManager.getApplicationInfo(context.getPackageName(),PackageManager.GET_META_DATA);
        return appInfo.sourceDir;
    }catch (PackageManager.NameNotFoundException e){
        return "invalid";
    }
}

然后在 UE 里使用 JNI 调用：

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if (JNIEnv* Env = FAndroidApplication::GetJavaEnv())
{
	jmethodID GetInstalledPakPathMethodID = FJavaWrapper::FindMethod(Env, FJavaWrapper::GameActivityClassID, "AndroidThunkJava_GetInstalledApkPath", "()Ljava/lang/String;", false);
	FString ResultApkPath = FJavaHelperEx::FStringFromLocalRef(Env, (jstring)FJavaWrapper::CallObjectMethod(Env, FJavaWrapper::GameActivityThis,GetInstalledPakPathMethodID));
}

其中 FJavaHelperEx::FStringFromLocalRef 是我封装的从 jstring 到 FString 的转换函数：

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namespace FJavaHelperEx
{
	FString FStringFromParam(JNIEnv* Env, jstring JavaString)
	{
		if (!Env || !JavaString || Env->IsSameObject(JavaString, NULL))
		{
			return {};
		}

		const auto chars = Env->GetStringUTFChars(JavaString, 0);
		FString ReturnString(UTF8_TO_TCHAR(chars));
		Env->ReleaseStringUTFChars(JavaString, chars);
		return ReturnString;
	}
	
	FString FStringFromLocalRef(JNIEnv* Env, jstring JavaString)
	{
		FString ReturnString = FStringFromParam(Env, JavaString);

		if (Env && JavaString)
		{
			Env->DeleteLocalRef(JavaString);
		}

		return ReturnString;
    
	}
}

获取的结果：

升级至 AndroidX 资料

看操作方式也是使用 UPL 来介入打包过程，先记录下。

为 APK 添加外部存储读写权限

在Project Settings-Platform-Android-Advanced APK Packaging-Extra Permissions下添加：

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android.permission.WRITE EXTERNAL STORAGE
android.permission.READ_EXTERNAL_STORAGE

AndroidP HTTP 请求错误

在 Android P 上使用 HTTP 请求上传数据会有以下错误提示：

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2018-10-10 16:39:21.312 31611-31646/com.xfhy.tinkerfirmdemo W/CrashReport: java.io.IOException: Cleartext HTTP traffic to android.bugly.qq.com not permitted
        at com.android.okhttp.HttpHandler$CleartextURLFilter.checkURLPermitted(HttpHandler.java:115)
        at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:458)
        at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:127)
        at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getOutputStream(HttpURLConnectionImpl.java:258)
        at com.tencent.bugly.proguard.ai.a(BUGLY:265)
        at com.tencent.bugly.proguard.ai.a(BUGLY:114)
        at com.tencent.bugly.proguard.al.run(BUGLY:355)
        at com.tencent.bugly.proguard.ak$1.run(BUGLY:723)
        at java.lang.Thread.run(Thread.java:764)
2018-10-10 16:39:21.312 31611-31646/com.xfhy.tinkerfirmdemo E/CrashReport: Failed to upload, please check your network.
2018-10-10 16:39:21.312 31611-31646/com.xfhy.tinkerfirmdemo D/CrashReport: Failed to execute post.
2018-10-10 16:39:21.312 31611-31646/com.xfhy.tinkerfirmdemo E/CrashReport: [Upload] Failed to upload(1): Failed to upload for no response!
2018-10-10 16:39:21.313 31611-31646/com.xfhy.tinkerfirmdemo E/CrashReport: [Upload] Failed to upload(1) userinfo: failed after many attempts

这需要我们在打包时把指定的域名给配置成白名单。

方法如下:

在 res/xml 下创建 network_security_config.xml 文件

填入以下内容（网址自行修改）：

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<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">android.bugly.qq.com</domain>
    </domain-config>
</network-security-config>

然后在 AndroifManifest.xml 中引用该文件：

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<application android:networkSecurityConfig="@xml/network_security_config"/>

重新打包即可，在运行时会有以下 Log：

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02-25 21:09:15.831 27760 27791 D NetworkSecurityConfig: Using Network Security Config from resource network_security_config debugBuild: true

Android 写入文件

当调用 FFileHelper::SaveArrayToFile 时：

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FFileHelper::SaveArrayToFile(TArrayView<const uint8>(data, delta), *path, &IFileManager::Get(), EFileWrite::FILEWRITE_Append));

在该函数内部会创建一个 FArchive 的对象来管理当前文件，其内部具有一个 IFileHandle 的对象Handle，在 Android 平台上是FFileHandleAndroid。

在 FArchive 中写入文件调用的是 Serialize，它又会调用Handle 的Write：

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bool FArchiveFileWriterGeneric::WriteLowLevel(const uint8* Src, int64 CountToWrite )
{
	return Handle->Write(Src, CountToWrite);
}

Android 的 Write 的实现为：

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// Runtime/Core/Private/Android/AndroidFile.h
virtual bool Write(const uint8* Source, int64 BytesToWrite) override
{
	CheckValid();
	if (nullptr != File->Asset)
	{
		// Can't write to assets.
		return false;
	}

	bool bSuccess = true;
	while (BytesToWrite)
	{
		check(BytesToWrite >= 0);
		int64 ThisSize = FMath::Min<int64>(READWRITE_SIZE, BytesToWrite);
		check(Source);
		if (__pwrite(File->Handle, Source, ThisSize, CurrentOffset) != ThisSize)
		{
			bSuccess = false;
			break;
		}
		CurrentOffset += ThisSize;
		Source += ThisSize;
		BytesToWrite -= ThisSize;
	}

	// Update the cached file length
	Length = FMath::Max(Length, CurrentOffset);

	return bSuccess;
}

可以看到是每次 1M 往文件里存的。

Android 写入文件错误码对照

根据 error code number 查找 error string.

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// bionic_errdefs.h
#ifndef __BIONIC_ERRDEF
#error "__BIONIC_ERRDEF must be defined before including this file"
#endif
__BIONIC_ERRDEF(0              ,   0, "Success" )
__BIONIC_ERRDEF(EPERM          ,   1, "Operation not permitted" )
__BIONIC_ERRDEF(ENOENT         ,   2, "No such file or directory" )
__BIONIC_ERRDEF(ESRCH          ,   3, "No such process" )
__BIONIC_ERRDEF(EINTR          ,   4, "Interrupted system call" )
__BIONIC_ERRDEF(EIO            ,   5, "I/O error" )
__BIONIC_ERRDEF(ENXIO          ,   6, "No such device or address" )
__BIONIC_ERRDEF(E2BIG          ,   7, "Argument list too long" )
__BIONIC_ERRDEF(ENOEXEC        ,   8, "Exec format error" )
__BIONIC_ERRDEF(EBADF          ,   9, "Bad file descriptor" )
__BIONIC_ERRDEF(ECHILD         ,  10, "No child processes" )
__BIONIC_ERRDEF(EAGAIN         ,  11, "Try again" )
__BIONIC_ERRDEF(ENOMEM         ,  12, "Out of memory" )
__BIONIC_ERRDEF(EACCES         ,  13, "Permission denied" )
__BIONIC_ERRDEF(EFAULT         ,  14, "Bad address" )
__BIONIC_ERRDEF(ENOTBLK        ,  15, "Block device required" )
__BIONIC_ERRDEF(EBUSY          ,  16, "Device or resource busy" )
__BIONIC_ERRDEF(EEXIST         ,  17, "File exists" )
__BIONIC_ERRDEF(EXDEV          ,  18, "Cross-device link" )
__BIONIC_ERRDEF(ENODEV         ,  19, "No such device" )
__BIONIC_ERRDEF(ENOTDIR        ,  20, "Not a directory" )
__BIONIC_ERRDEF(EISDIR         ,  21, "Is a directory" )
__BIONIC_ERRDEF(EINVAL         ,  22, "Invalid argument" )
__BIONIC_ERRDEF(ENFILE         ,  23, "File table overflow" )
__BIONIC_ERRDEF(EMFILE         ,  24, "Too many open files" )
__BIONIC_ERRDEF(ENOTTY         ,  25, "Not a typewriter" )
__BIONIC_ERRDEF(ETXTBSY        ,  26, "Text file busy" )
__BIONIC_ERRDEF(EFBIG          ,  27, "File too large" )
__BIONIC_ERRDEF(ENOSPC         ,  28, "No space left on device" )
__BIONIC_ERRDEF(ESPIPE         ,  29, "Illegal seek" )
__BIONIC_ERRDEF(EROFS          ,  30, "Read-only file system" )
__BIONIC_ERRDEF(EMLINK         ,  31, "Too many links" )
__BIONIC_ERRDEF(EPIPE          ,  32, "Broken pipe" )
__BIONIC_ERRDEF(EDOM           ,  33, "Math argument out of domain of func" )
__BIONIC_ERRDEF(ERANGE         ,  34, "Math result not representable" )
__BIONIC_ERRDEF(EDEADLK        ,  35, "Resource deadlock would occur" )
__BIONIC_ERRDEF(ENAMETOOLONG   ,  36, "File name too long" )
__BIONIC_ERRDEF(ENOLCK         ,  37, "No record locks available" )
__BIONIC_ERRDEF(ENOSYS         ,  38, "Function not implemented" )
__BIONIC_ERRDEF(ENOTEMPTY      ,  39, "Directory not empty" )
__BIONIC_ERRDEF(ELOOP          ,  40, "Too many symbolic links encountered" )
__BIONIC_ERRDEF(ENOMSG         ,  42, "No message of desired type" )
__BIONIC_ERRDEF(EIDRM          ,  43, "Identifier removed" )
__BIONIC_ERRDEF(ECHRNG         ,  44, "Channel number out of range" )
__BIONIC_ERRDEF(EL2NSYNC       ,  45, "Level 2 not synchronized" )
__BIONIC_ERRDEF(EL3HLT         ,  46, "Level 3 halted" )
__BIONIC_ERRDEF(EL3RST         ,  47, "Level 3 reset" )
__BIONIC_ERRDEF(ELNRNG         ,  48, "Link number out of range" )
__BIONIC_ERRDEF(EUNATCH        ,  49, "Protocol driver not attached" )
__BIONIC_ERRDEF(ENOCSI         ,  50, "No CSI structure available" )
__BIONIC_ERRDEF(EL2HLT         ,  51, "Level 2 halted" )
__BIONIC_ERRDEF(EBADE          ,  52, "Invalid exchange" )
__BIONIC_ERRDEF(EBADR          ,  53, "Invalid request descriptor" )
__BIONIC_ERRDEF(EXFULL         ,  54, "Exchange full" )
__BIONIC_ERRDEF(ENOANO         ,  55, "No anode" )
__BIONIC_ERRDEF(EBADRQC        ,  56, "Invalid request code" )
__BIONIC_ERRDEF(EBADSLT        ,  57, "Invalid slot" )
__BIONIC_ERRDEF(EBFONT         ,  59, "Bad font file format" )
__BIONIC_ERRDEF(ENOSTR         ,  60, "Device not a stream" )
__BIONIC_ERRDEF(ENODATA        ,  61, "No data available" )
__BIONIC_ERRDEF(ETIME          ,  62, "Timer expired" )
__BIONIC_ERRDEF(ENOSR          ,  63, "Out of streams resources" )
__BIONIC_ERRDEF(ENONET         ,  64, "Machine is not on the network" )
__BIONIC_ERRDEF(ENOPKG         ,  65, "Package not installed" )
__BIONIC_ERRDEF(EREMOTE        ,  66, "Object is remote" )
__BIONIC_ERRDEF(ENOLINK        ,  67, "Link has been severed" )
__BIONIC_ERRDEF(EADV           ,  68, "Advertise error" )
__BIONIC_ERRDEF(ESRMNT         ,  69, "Srmount error" )
__BIONIC_ERRDEF(ECOMM          ,  70, "Communication error on send" )
__BIONIC_ERRDEF(EPROTO         ,  71, "Protocol error" )
__BIONIC_ERRDEF(EMULTIHOP      ,  72, "Multihop attempted" )
__BIONIC_ERRDEF(EDOTDOT        ,  73, "RFS specific error" )
__BIONIC_ERRDEF(EBADMSG        ,  74, "Not a data message" )
__BIONIC_ERRDEF(EOVERFLOW      ,  75, "Value too large for defined data type" )
__BIONIC_ERRDEF(ENOTUNIQ       ,  76, "Name not unique on network" )
__BIONIC_ERRDEF(EBADFD         ,  77, "File descriptor in bad state" )
__BIONIC_ERRDEF(EREMCHG        ,  78, "Remote address changed" )
__BIONIC_ERRDEF(ELIBACC        ,  79, "Can not access a needed shared library" )
__BIONIC_ERRDEF(ELIBBAD        ,  80, "Accessing a corrupted shared library" )
__BIONIC_ERRDEF(ELIBSCN        ,  81, ".lib section in a.out corrupted" )
__BIONIC_ERRDEF(ELIBMAX        ,  82, "Attempting to link in too many shared libraries" )
__BIONIC_ERRDEF(ELIBEXEC       ,  83, "Cannot exec a shared library directly" )
__BIONIC_ERRDEF(EILSEQ         ,  84, "Illegal byte sequence" )
__BIONIC_ERRDEF(ERESTART       ,  85, "Interrupted system call should be restarted" )
__BIONIC_ERRDEF(ESTRPIPE       ,  86, "Streams pipe error" )
__BIONIC_ERRDEF(EUSERS         ,  87, "Too many users" )
__BIONIC_ERRDEF(ENOTSOCK       ,  88, "Socket operation on non-socket" )
__BIONIC_ERRDEF(EDESTADDRREQ   ,  89, "Destination address required" )
__BIONIC_ERRDEF(EMSGSIZE       ,  90, "Message too long" )
__BIONIC_ERRDEF(EPROTOTYPE     ,  91, "Protocol wrong type for socket" )
__BIONIC_ERRDEF(ENOPROTOOPT    ,  92, "Protocol not available" )
__BIONIC_ERRDEF(EPROTONOSUPPORT,  93, "Protocol not supported" )
__BIONIC_ERRDEF(ESOCKTNOSUPPORT,  94, "Socket type not supported" )
__BIONIC_ERRDEF(EOPNOTSUPP     ,  95, "Operation not supported on transport endpoint" )
__BIONIC_ERRDEF(EPFNOSUPPORT   ,  96, "Protocol family not supported" )
__BIONIC_ERRDEF(EAFNOSUPPORT   ,  97, "Address family not supported by protocol" )
__BIONIC_ERRDEF(EADDRINUSE     ,  98, "Address already in use" )
__BIONIC_ERRDEF(EADDRNOTAVAIL  ,  99, "Cannot assign requested address" )
__BIONIC_ERRDEF(ENETDOWN       , 100, "Network is down" )
__BIONIC_ERRDEF(ENETUNREACH    , 101, "Network is unreachable" )
__BIONIC_ERRDEF(ENETRESET      , 102, "Network dropped connection because of reset" )
__BIONIC_ERRDEF(ECONNABORTED   , 103, "Software caused connection abort" )
__BIONIC_ERRDEF(ECONNRESET     , 104, "Connection reset by peer" )
__BIONIC_ERRDEF(ENOBUFS        , 105, "No buffer space available" )
__BIONIC_ERRDEF(EISCONN        , 106, "Transport endpoint is already connected" )
__BIONIC_ERRDEF(ENOTCONN       , 107, "Transport endpoint is not connected" )
__BIONIC_ERRDEF(ESHUTDOWN      , 108, "Cannot send after transport endpoint shutdown" )
__BIONIC_ERRDEF(ETOOMANYREFS   , 109, "Too many references: cannot splice" )
__BIONIC_ERRDEF(ETIMEDOUT      , 110, "Connection timed out" )
__BIONIC_ERRDEF(ECONNREFUSED   , 111, "Connection refused" )
__BIONIC_ERRDEF(EHOSTDOWN      , 112, "Host is down" )
__BIONIC_ERRDEF(EHOSTUNREACH   , 113, "No route to host" )
__BIONIC_ERRDEF(EALREADY       , 114, "Operation already in progress" )
__BIONIC_ERRDEF(EINPROGRESS    , 115, "Operation now in progress" )
__BIONIC_ERRDEF(ESTALE         , 116, "Stale NFS file handle" )
__BIONIC_ERRDEF(EUCLEAN        , 117, "Structure needs cleaning" )
__BIONIC_ERRDEF(ENOTNAM        , 118, "Not a XENIX named type file" )
__BIONIC_ERRDEF(ENAVAIL        , 119, "No XENIX semaphores available" )
__BIONIC_ERRDEF(EISNAM         , 120, "Is a named type file" )
__BIONIC_ERRDEF(EREMOTEIO      , 121, "Remote I/O error" )
__BIONIC_ERRDEF(EDQUOT         , 122, "Quota exceeded" )
__BIONIC_ERRDEF(ENOMEDIUM      , 123, "No medium found" )
__BIONIC_ERRDEF(EMEDIUMTYPE    , 124, "Wrong medium type" )
__BIONIC_ERRDEF(ECANCELED      , 125, "Operation Canceled" )
__BIONIC_ERRDEF(ENOKEY         , 126, "Required key not available" )
__BIONIC_ERRDEF(EKEYEXPIRED    , 127, "Key has expired" )
__BIONIC_ERRDEF(EKEYREVOKED    , 128, "Key has been revoked" )
__BIONIC_ERRDEF(EKEYREJECTED   , 129, "Key was rejected by service" )
__BIONIC_ERRDEF(EOWNERDEAD     , 130, "Owner died" )
__BIONIC_ERRDEF(ENOTRECOVERABLE, 131, "State not recoverable" )

#undef __BIONIC_ERRDEF

UE 项目启动参数

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：

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// 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。

Android 设置宽高比

在Project Settings-Platforms-Android-Maximum support aspect ratio的值，默认是 2.1，但是在全面屏的情况下会有黑边。

它控制的值是 AndroidManifest.xml 中的值：

1
<meta-data android:name="android.max_aspect" android:value="2.1"/>

我目前设置的值是 2.5.

注：Enable FullScreen Immersive on KitKat and above devices控制的是进入游戏时是否隐藏虚拟按键。