some questions about  JNI.
lazarus / 43-Android

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ROCABDEL · 2012-06-19 21:38

hello everyone !
I am trying to change bass.pas by introducing support for jni, to
facilitate the use of this library multiplatform, but I am blocking
here:

Code: [Select]public interface SYNCPROC
        {
                void SYNCPROC(int handle, int channel, int data,
Object user);
        }
public static native int BASS_ChannelSetSync(int handle, int type,
long param, SYNCPROC proc, Object user); 

What is the signature of BASS_ChannelSetSync ? and how i can call it ?

i proceed like this :

Code: [Select]javaMethod_Bass_BASS_ChannelSetSync:=
javaEnvRef^^.GetStaticMethodID(javaEnvRef, javaClass_Bass,
'BASS_ChannelSetSync', '(IIJLL)I');// Error in the first 'L' i think

//I am not yet arrived here, only to correct me
lParams[0].i:= Myhandle;                   //handle
lParams[1].i:= 0                                    //type
lParams[2].j:= 0;                                   //param
lParams[3].l:= @Sync_CallBack;     //proc
lParams[4].l := Self;                             //user
lRetInt := javaEnvRef^^.CallStaticIntMethodA(javaEnvRef,
javaClass_Bass, javaMethod_Bass_BASS_ChannelSetSync, @lParams[0]);


correct the code or links are welcome 

thank you for your time

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felipemdc · 2012-06-20 05:33

You are using the L signature wrongly. You cannot use just L, you need
to write L<path to the class>;

For example: Ljava/lang/Object;
For the other one something like: Lorg/jouvieje/bass/Bass/SYNCPROC;

About the parameters, you are getting them wrong here:

lParams[4].l := Self;                             //user

You cannot use Self, because your Self is a Pascal object and the
routine expects a Java Object. You can create a new Java object using
JNI: http://wiki.freepascal.org/Android_Programming#Example_1:_Creatin
g_a_Java_object_and_calling_a_Java_method

Also here:

lParams[3].l:= @Sync_CallBack;     //proc

This is also wrong, you need to pass a Java object here, not a pointer
to what is probably a procedure. But now is the nasty thing. You need
an object of a class which implements that interface. So far I don't
know how to do that in JNI or if it is possible. I asked a question
about this in the android-ndk group, let's see if anyone answers.

My solution to cases which require using interfaces so far has been
creating a new routine in the .java file of the project which makes
the necessary call. And then I call this routine via JNI. See this
commit for example: http://svn.freepascal.org/cgi-
bin/viewvc.cgi?view=rev&root=lazarus&revision=37692

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ROCABDEL · 2012-06-20 18:33

thank you very much felipemdc for your availability.
I tried this:
Code: [Select]javaMethod_Bass_BASS_ChannelSetSync:=
javaEnvRef^^.GetStaticMethodID(javaEnvRef, javaClass_Bass,
'BASS_ChannelSetSync', '(IIJLcom/un4seen/bass/BASS/SYNCPROC;L)I');
but the program crash when I run 

for the second suggestion I do not think it's easy for me because it's
the same library that she must have called my program..

I'll wait for the answer of your friends in android-ndk group maybe
they will help us 

if 'I manage to solve the problem I let you know..

for those who are interested in. Here are links to this audio library
:

-http://www.un4seen.com/
 -Win32 http://www.un4seen.com/download.php?bass24
 -Win64 http://www.un4seen.com/forum/?topic=9038.0
 -OSX http://www.un4seen.com/download.php?bass24-osx
 -Linux http://www.un4seen.com/download.php?bass24-linux
 -ARM Linux http://www.un4seen.com/forum/?topic=13804.0   
 -Android http://www.un4seen.com/forum/?topic=13225.0
 -iOS http://www.un4seen.com/forum/?topic=10910.0
 -WinCE http://www.un4seen.com/forum/?topic=9534.0


thank you again and Sorry for my English .

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felipemdc · 2012-06-20 20:35

Quote from: ROCABDEL on June 20, 2012, 08:33:46 pmthank you very much
felipemdc for your availability.
I tried this:
Code: [Select]javaMethod_Bass_BASS_ChannelSetSync:=
javaEnvRef^^.GetStaticMethodID(javaEnvRef, javaClass_Bass,
'BASS_ChannelSetSync', '(IIJLcom/un4seen/bass/BASS/SYNCPROC;L)I');
but the program crash when I run 
Your second L is wrong. It has no type. It should be:
Ljava/lang/Object;

Quotefor the second suggestion I do not think it's easy for me because
it's the same library that she must have called my program..

I'll wait for the answer of your friends in android-ndk group maybe
they will help us 
To my surprise the answer was positive. It is possible to declare a
new class and load it to the virtual machine. But I still don't
dominate how to do that. It will probably be rather complex, but for
me that's not a big deal. Here is the android-ndk thread about this:

https://groups.google.com/forum/?fromgroups#!topic/android-
ndk/SRgy93Un8vM

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ROCABDEL · 2012-06-21 20:27

I also asked in some French forums if anyone can give us a track, and
I am trying to read some docs in English 
http://www.pacifier.com/~mmead/jni/delphi/index.html
http://java.sun.com/docs/books/jni/
http://docs.oracle.com/javase/1.4.2/docs/guide/jni/spec/jniTOC.html

thank you again felipemdc and good luck