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POjni callback works for java types, but not c types
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copied!<p>I have followed the advice at <a href="https://stackoverflow.com/questions/4313004/registering-java-function-as-a-callback-in-c-function">registering java function as a callback in C function</a> and can callback with "simple" types such as integer and string, e.g.:</p> <pre><code>jstring js = (*env)->NewStringUTF(env, "hello"); (*env)->CallStaticVoidMethod(env, cls, methodid, js); </code></pre> <p>However, if I am trying to do the same with C datatypes which have been wrapped with SWIG, I am only getting null pointers in Java. In the C part they are definitely not 0. Do they need to be treated differently?</p> <p>[EDIT:] Some more information:</p> <p>As stated above, char*/string is working for me as well. I am looking for a solution for C struct's, which have been wrapped by SWIG and have been allocated in Java.</p> <p>E.g.:</p> <pre><code>typedef struct { unsigned short length; unsigned short value; } lv_t; </code></pre> <p>is getting wrapped by SWIG, so I can use it in Java:</p> <pre><code>lv_t lv; lv = modulename.modulename_new_lv(); lv.setLength(1); lv.setValue(2); </code></pre> <p>Then I will give this struct from Java to C:</p> <pre><code>modulename.send(lv); </code></pre> <p>C will send it over the network, receive some reply and change the values in lv. Now, this should give the modified lv back to Java.</p> <pre><code>void jni_call_received_hook(lv_t* lv){ JNIEnv* m_env; (*m_vm)->AttachCurrentThread(m_vm, (void**) &m_env, NULL ); jclass cls = (*m_env)->FindClass( m_env, "gui/StateMachine" ); jmethodID mid = (*m_env)->GetStaticMethodID(m_env, cls, "callReceivedEvent", "(Lcom/something/modulename/jni/lv_t;)V"); if (mid == 0){ log(E, "Unable to find method for callback"); return; } // what to do here to create a jobject? jobject lv_j = ...; (*m_env)->CallStaticVoidMethod(m_env, cls, mid, lv_j); </code></pre> <p>}</p> <p>Which calls:</p> <pre><code>public static void messageHandler(lv_t lv) { System.out.println("messageHandler()."); System.out.println("lv " + lv); } </code></pre>

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