High level: C++ and JNI data transfer

In some special cases it is necessary to transfer simple or even complex data to the host application. For this purpose it is fairly enough to only work with static methods. The ARES Touch SDK provides a handful helper classes to avoid working directly with the JNI interfaces and Java environment. The utility class is called FxJavaUtils and provides a large set of classes. These are the steps to address a simple data transfer between the host app and the C++ app part and vice versa.

1.Transfer data from C++ to Java JAVA C++

1.1 Create a Java class and add a public static method

public static RETURNTYPE CPP_TO_JAVA( PARAMS );

The RETURNTYPE as well as the PARAMS must be declared with Java known data types. The method name CPP_TO_JAVA does not need to contain characters like _ , may be just CPPTOJAVA.

Note: Whenever the code inside the Java method manipulates the UI of the host application, the code must be executed from the UI thread.

JAVA

public class JAVA_CLASS
{
...
public static RETURNTYPE CPP_TO_JAVA( [PARAMS ...] )
{
    CFxARESInstance.instance().runOnUiThread(new Runnable()
    {
        @Override
        public void run()
        {
            
        }
    });
}
...
}

1.1 Call a Java method from C++ (Simple Data) JAVA C++

The SDK ships a helper class CFxStaticInvocation that takes care about most of the JNI settings and can be used quite fast. The class CFxStaticInvocation constructor only requires the location of the Java class PATH_OF_JAVA_CLASS, the java class method name JAVA_METHOD and the Java method signature JAVA_METHOD_SIGNATURE. If every detail matches perfectly it is only necessary to call it using the void Call( bool bWithParameters = false, ... ); method of CFxStaticInvocation.

C++

CFxStaticInvocation obj( "PATH_OF_JAVA_CLASS", "JAVA_METHOD", "JAVA_METHOD_SIGNATURE" );
obj.Call( true, [PARAMS, ...] );

Specifying the Java class method signature is the only challenging part. Here is a list of the matching Java / JNI signature pairs.

Sample (None executable code):
JAVA

public class Geometry
{
...
public static void PointAdded( final double x , final double y )
{
    CFxARESInstance.instance().runOnUiThread(new Runnable()
    {
        @Override
        public void run()
        {
            //
        }
    });
}
...
}

C++

CFxStaticInvocation invocation( "com/domain/Geometry", "PointAdded", "(DD)V" );
invocation.Call( true, 100.23, 100.67 );

For further samples look for any use of CFxStaticInvocation in the Android projects.

1.2 Call a Java method from C++ (Complex Data) JAVA C++

Coming soon …

1.3 Return values back from C++ to Java JAVA C++

Coming soon …