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JNI Issues

Hi Guys,

Happy holidays.

I am stuck with an issue. I am working on a project that needs me to communicate with GameActivity.Java from C++. I am calling a blueprint, that calls a Java function through C++ using JNI. I am having problems even declaring JNI objects like JNIEnv and JavaVM. I am using MacOS to develop this project and I am not modifying any source code. I am developing a plugin and am putting all my code into that plugin and right now, I am writing the code for Android.

I am trying to something like this: https://answers.unrealengine.com/questions/412020/what-is-correct-and-present-method-of-packaging-a.html

I am attaching the following:

  1. Error Message
  2. My plugin’s build.cs file
  3. C++ Header File
  4. C++ source file

Thanks Again
d0d0

**Here is my error message:
**




Recompiling UObjectPlugin...
Launching UnrealBuildTool... [/Users/Shared/UnrealEngine/4.13/Engine/Binaries/DotNET/UnrealBuildTool.exe MyProject -ModuleWithSuffix UObjectPlugin 1143 Mac Development -editorrecompile -canskiplink "/Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/MyProject.uproject" ]
CompilerResultsLog: New page: Compilation - Dec 1, 2016, 2:24:34 AM
CompilerResultsLog: Info 
CompilerResultsLog: Info Running Mono...
CompilerResultsLog: Info 
CompilerResultsLog: Info Setting up Mono
CompilerResultsLog: Info /Users/Shared/UnrealEngine/4.13/Engine /Users/Shared/UnrealEngine/4.13/Engine/Binaries/Mac
CompilerResultsLog: Info Compiling game modules for hot reload
CompilerResultsLog: Info Compiling with MacOSX SDK 10.12
CompilerResultsLog: Info Parsing headers for MyProjectEditor
CompilerResultsLog: Info   Running UnrealHeaderTool "/Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/MyProject.uproject" "/Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Intermediate/Build/Mac/MyProjectEditor/Development/MyProjectEditor.uhtmanifest" -LogCmds="loginit warning, logexit warnin
g, logdatabase error" -Unattended -WarningsAsErrors -installed
CompilerResultsLog: Info Reflection code generated for MyProjectEditor in 6.6998022 seconds
CompilerResultsLog: Info Performing 3 actions (4 in parallel)
CompilerResultsLog: Info [1/3] Compile Module.UObjectPlugin.cpp
CompilerResultsLog: Info [2/3] Compile UObjectPlugin.generated.cpp
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Inc/UObjectPlugin/UObjectPlugin.generated.cpp:9:
CompilerResultsLog: Info In file included from ../../../../../d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Inc/UObjectPlugin/UObjectPlugin.generated.dep.h:9:
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:19:8: error: unknown type name 'JavaVM'
CompilerResultsLog: Info extern JavaVM *jvm;
CompilerResultsLog: Info        ^
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Development/UObjectPlugin/Module.UObjectPlugin.cpp:2:
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Private/MyPluginObject.cpp:4:
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:19:8: error: unknown type name 'JavaVM'
CompilerResultsLog: Info extern JavaVM *jvm;
CompilerResultsLog: Info        ^
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:20:8: error: unknown type name 'JNIEnv'
CompilerResultsLog: Info extern  JNIEnv *env;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:20:8: error: unknown type name 'JNIEnv'
CompilerResultsLog: Info extern  JNIEnv *env;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Development/UObjectPlugin/Module.UObjectPlugin.cpp:2:
CompilerResultsLog: Info /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Private/MyPluginObject.cpp:32:2: error: unknown type name 'JavaVM'
CompilerResultsLog: Info         JavaVM *jvm;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Private/MyPluginObject.cpp:33:2: error: unknown type name 'JNIEnv'
CompilerResultsLog: Info         JNIEnv *env;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info 2 errors generated.
CompilerResultsLog: Info 4 errors generated.
CompilerResultsLog: Info ERROR: UBT ERROR: Failed to produce item: /Users/d0d0/Documents/Projects/UnrealProjects/MyProject 4.13 - 6/Plugins/UObjectPlugin/Binaries/Mac/UE4Editor-UObjectPlugin-1143.dylib
CompilerResultsLog: Info Total build time: 17.02 seconds
LogMainFrame: MainFrame: Module compiling took 17.909 seconds
Warning: HotReload failed, recompile failed
Warning: RebindPackages failed because the compiler could not be started.



  1. Here is my projects build.cs file:



// Copyright 1998-2016 Epic Games, Inc. All Rights Reserved.

namespace UnrealBuildTool.Rules
{
	public class UObjectPlugin : ModuleRules
	{
		public UObjectPlugin(TargetInfo Target)
		{
			PublicIncludePaths.AddRange(
				new string] {
					// ... add public include paths required here ...
					"/Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home/include/",
					
				}
				);

			PrivateIncludePaths.AddRange(
				new string] {
					"Developer/UObjectPlugin/Private",
					// ... add other private include paths required here ...
						"../../../../Source/Runtime/Core/Private", 
						"../../../../Source/Runtime/Launch/Private",
						"../../../../Source/Runtime/Core/Private/Android", 
						"../../../../Source/Runtime/Launch/Private/Android",
						"/Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home/include/",
				}
				);

			PublicDependencyModuleNames.AddRange(
				new string]
				{
					"Core",
					"CoreUObject",
					// ... add other public dependencies that you statically link with here ...
					"Engine", 
					"InputCore", 
					"Launch", 
				}
				);

			PrivateDependencyModuleNames.AddRange(
				new string]
				{
					// ... add private dependencies that you statically link with here ...
					"Core",
					"CoreUObject",
					"Engine", 
					"InputCore", 
					"Launch", 
				}
				);

			DynamicallyLoadedModuleNames.AddRange(
				new string]
				{
					// ... add any modules that your module loads dynamically here ...
				}
				);
		}
	}
}



**3) Here is my Header file
**




// Copyright 1998-2016 Epic Games, Inc. All Rights Reserved.

#pragma once

#if PLATFORM_ANDROID
	#include <jni.h>
	#include "AndroidJNI.h"
	#include "AndroidJava.h"
	#include "AndroidApplication.h"
	#include <Android/asset_manager.h>
	#include <Android/asset_manager_jni.h>

#endif


#include "MyPluginObject.generated.h"


extern JavaVM *jvm;
extern	JNIEnv *env;


/**
 * Example UStruct declared in a plugin module 
 */
USTRUCT()
struct FMyPluginStruct
{
	GENERATED_USTRUCT_BODY()
 
	UPROPERTY()
	FString TestString;
};
 

/**
 * Example of declaring a UObject in a plugin module
 */
UCLASS()
class UMyPluginObject : public UObject
{
	GENERATED_UCLASS_BODY()

public:
	
	UFUNCTION( BlueprintCallable, Category = Karmik)
		void callMapsActivity();
		

	
		 void  AndroidThunkCpp_callMapsActivity();


private:

	UPROPERTY()
	FMyPluginStruct MyStruct;

};






4) Here is my Source file




// Copyright 1998-2016 Epic Games, Inc. All Rights Reserved.

#include "UObjectPluginPrivatePCH.h"
#include "MyPluginObject.h"

#if PLATFORM_ANDROID
	#include <jni.h>
	#include "AndroidJNI.h"
	#include "AndroidJava.h"
	#include "AndroidApplication.h"
	#include <Android/asset_manager.h>
	#include <Android/asset_manager_jni.h>

#endif




UMyPluginObject::UMyPluginObject( const FObjectInitializer& ObjectInitializer )
	: Super( ObjectInitializer )
{
}


void UMyPluginObject::callMapsActivity()
{
	// This is going to be the BluePrint function that calls AndroidThunkCpp_callMapsActivity()
}



	JavaVM *jvm;
	JNIEnv *env;
	
void UMyPluginObject::AndroidThunkCpp_callMapsActivity()
{
	// This will call the java method to invoke MapsActivity
	
//   if (JNIEnv* Env = FAndroidApplication::GetJavaEnv())
//   {
//	       static jmethodID callMapsActivityMethod = FJavaWrapper::FindMethod(Env, FJavaWrapper::GameActivityClassID, "AndroidThunkJava_callMapsActivity", "(Z)V", false);
//		   FJavaWrapper::CallVoidMethod(Env, FJavaWrapper::GameActivityThis, callMapsActivityMethod, false);
//   }
	
}






You should just need to include these:


#include "Android/AndroidJNI.h"
#include "Android/AndroidApplication.h"

And in the Build.cs you don’t need the /Library, the Private/Android shouldn’t be specified (you should do like above). I think this would do what you want:


			PublicDependencyModuleNames.AddRange(
				new string]
				{
					"Core",
				}
			);

			PublicIncludePathModuleNames.AddRange(
				new string]
				{
					"Core",
					"Launch",
				}
			);

Looks like you are compiling for MAC (and I’m not sure Android supports plugins does it?).

jni.h is only included for Android.

Or I’m missing something?

HI Chris,

Thanks so much for your quick response.

Like you suggested, I removed all the private dependencies and paths in the build.cs file and I also changed the includes in the header and source files to #include “Android/AndroidJNI.h”

I am getting the same error as before.

Here is the strange part, my other c++/Blueprint code is working fine. The moment, I try JNI related coding, I get these errors.

Thanks
d0d0

Here are the code changes I made to the buil.cs file




// Copyright 1998-2016 HazardNetworking, Inc. All Rights Reserved.

namespace UnrealBuildTool.Rules
{
	public class UObjectPlugin : ModuleRules
	{
		public UObjectPlugin(TargetInfo Target)
		{
			PublicIncludePaths.AddRange(
				new string] {
					"Developer/UObjectPlugin/Public"
					// ... add public include paths required here ...
					//"/Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home/include/",
					
				}
				);

			PrivateIncludePaths.AddRange(
				new string] {
					"Developer/UObjectPlugin/Private",
					// ... add other private include paths required here ...
					//	"../../../../Source/Runtime/Core/Private", 
					//	"../../../../Source/Runtime/Launch/Private",
					//	"../../../../Source/Runtime/Core/Private/Android", 
					//	"../../../../Source/Runtime/Launch/Private/Android",
					//	"/Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home/include/",
				}
				);

			PublicDependencyModuleNames.AddRange(
				new string]
				{
					"Core",
					"CoreUObject",
					// ... add other public dependencies that you statically link with here ...
					"Engine", 
					"InputCore", 
					"Launch", 
				}
				);

				PublicIncludePathModuleNames.AddRange(
					new string]
				{

					"Core",
					"CoreUObject",
					// ... add other public dependencies that you statically link with here ...
					"Engine", 
					"InputCore", 
					"Launch", 
				}
				);

			PrivateDependencyModuleNames.AddRange(
				new string]
				{
					// ... add private dependencies that you statically link with here ...
					//"Core",
					//"CoreUObject",
					//"Engine", 
					//"InputCore", 
					//"Launch", 
				}
				);

			DynamicallyLoadedModuleNames.AddRange(
				new string]
				{
					// ... add any modules that your module loads dynamically here ...
				}
				);
		}
	}
}



Here is the error:




Recompiling UObjectPlugin...
Launching UnrealBuildTool... [/Users/Shared/UnrealEngine/4.13/Engine/Binaries/DotNET/UnrealBuildTool.exe hazardnetworking -ModuleWithSuffix UObjectPlugin 1130 Mac Development -editorrecompile -canskiplink "/Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/hazardnetworking.uproject" ]
CompilerResultsLog: New page: Compilation - Dec 1, 2016, 5:09:06 AM
CompilerResultsLog: Info 
CompilerResultsLog: Info Running Mono...
CompilerResultsLog: Info 
CompilerResultsLog: Info Setting up Mono
CompilerResultsLog: Info /Users/Shared/UnrealEngine/4.13/Engine /Users/Shared/UnrealEngine/4.13/Engine/Binaries/Mac
CompilerResultsLog: Info Compiling game modules for hot reload
CompilerResultsLog: Info Compiling with MacOSX SDK 10.12
CompilerResultsLog: Info Parsing headers for hazardnetworkingEditor
CompilerResultsLog: Info   Running UnrealHeaderTool "/Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/hazardnetworking.uproject" "/Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Intermediate/Build/Mac/hazardnetworkingEditor/Development/hazardnetworkingEditor.uhtmanifest" -LogCmds="loginit warning, logexit warnin
g, logdatabase error" -Unattended -WarningsAsErrors -installed
CompilerResultsLog: Info Reflection code generated for hazardnetworkingEditor in 7.2823505 seconds
CompilerResultsLog: Info Performing 3 actions (4 in parallel)
CompilerResultsLog: Info [2/3] Compile UObjectPlugin.generated.cpp
CompilerResultsLog: Info [1/3] Compile Module.UObjectPlugin.cpp
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Inc/UObjectPlugin/UObjectPlugin.generated.cpp:9:
CompilerResultsLog: Info In file included from ../../../../../d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Inc/UObjectPlugin/UObjectPlugin.generated.dep.h:9:
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Development/UObjectPlugin/Module.UObjectPlugin.cpp:2:
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Private/MyPluginObject.cpp:4:
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:19:8: error: unknown type name 'JavaVM'
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:19:8: error: unknown type name 'JavaVM'
CompilerResultsLog: Info extern JavaVM *jvm;
CompilerResultsLog: Info        ^
CompilerResultsLog: Info extern JavaVM *jvm;
CompilerResultsLog: Info        ^
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:20:8: error: unknown type name 'JNIEnv'
CompilerResultsLog: Info extern  JNIEnv *env;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info ../../../../../d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Classes/MyPluginObject.h:20:8: error: unknown type name 'JNIEnv'
CompilerResultsLog: Info extern  JNIEnv *env;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info In file included from /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Intermediate/Build/Mac/UE4Editor/Development/UObjectPlugin/Module.UObjectPlugin.cpp:2:
CompilerResultsLog: Info /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Private/MyPluginObject.cpp:32:2: error: unknown type name 'JavaVM'
CompilerResultsLog: Info         JavaVM *jvm;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Source/UObjectPlugin/Private/MyPluginObject.cpp:33:2: error: unknown type name 'JNIEnv'
CompilerResultsLog: Info         JNIEnv *env;
CompilerResultsLog: Info         ^
CompilerResultsLog: Info 2 errors generated.
CompilerResultsLog: Info 4 errors generated.
CompilerResultsLog: Info ERROR: UBT ERROR: Failed to produce item: /Users/d0d0/Documents/Projects/UnrealProjects/hazardnetworking 4.13 - 6/Plugins/UObjectPlugin/Binaries/Mac/UE4Editor-UObjectPlugin-1130.dylib
CompilerResultsLog: Info Total build time: 21.04 seconds
LogMainFrame: MainFrame: Module compiling took 22.082 seconds



Hi theonecalledatom,

From what I understand: there are two c++ compilers used by unreal. Unreal uses clang to compile itself including plugins and other c++ coding. Then for sections that says, android only, it uses another compiler for android NDK, g++.

I understand what you are pointing to, let me try moving the jni.h out of the android specific section and rerun the code.

Thanks.
d0d0

Yes, Mac will be compiled by Xcode and Android by clang from the NDK toolchain.

You need to protect any references to Android dependencies with #if PLATFORM_ANDROID / #endif or it will fail to compile for anything but Android.

All,

I am able to get the code to work now. These are the changes I made:

  1. I had to do all my JNI or Android specific coding between #if PLATFORM_ANDROID and #endif. Some of my coding was out of this platform specific structure and it did not compile.
  2. In my build.cs file, I removed the dependencies on the module ‘Launch’. For some reason, I get a linker error whenever I include ‘Launch’ module. Here is a link to this issue: https://answers.unrealengine.com/questions/521176/linker-error-trying-to-find-dylib-files.html#answer-531520

But for now, I am able to proceed with my coding.

Thanks Again for all your help.
d0d0

That’s because the Launch module is meant for Engine-only use I believe, not standalone projects or plugins. I made the same mistake as well.

Ok… Thanks. that makes sense

Every plugin I’ve created for Android requires the Launch module. You may need to wrap the inclusion of the Launch module in a conditional statement in your build.cs file. So…