Accessing a Java class from my application...

[Drummer1972 0]

hello. 
I have been trying for three weeks to get my app to access a simple java class I have created and I always get the same error when executing the line 'Error: Java class not found: com/my/MySimpleClass'.

    const char* jclassName = “com/embarcadero/MySimpleClass”;

    jClass = env->FindClass(jclassName);

MySimpleClass.java is :

 

package com.embarcadero;

 import android.util.Log;

 public class MySimpleClass {

 

    public void loadLibrary(String jarPath) {

        try {

                 Log.d("MySimpleClass", "Load JAR : " + jarPath);

             }  catch (Exception e) {

               Log.e("MySimpleClass", "loading error JAR: " + e.getMessage());

           }

      }

    public void sayHello()

     {

        Log.d("MySimpleClass", "¡Hello from the Java class!");

    }

}

The code that I use from my small app (it only consists of one Form) is

#ifndef MenuH
#define MenuH
//---------------------------------------------------------------------------
#include <System.Classes.hpp>
#include <FMX.Controls.hpp>
#include <FMX.Forms.hpp>
#include <FMX.StdCtrls.hpp>
#include <Androidapi.JNI.hpp>           // Importante para JNI
#include <Androidapi.JNI.JavaTypes.hpp> // Importante para JNI
#include <System.Rtti.hpp>
#include <FMX.Objects.hpp>
#include <FMX.Types.hpp>


class TFMenu : public TForm
{
__published:    // IDE-managed Components
    TText *Text1;
private:    // User declarations

    jclass jClass;
    jobject jObject;
    jmethodID methodId;

public:        // User declarations
    __fastcall TFMenu(TComponent* Owner);
    __fastcall ~TFMenu();  //Destructor

};

#include <fmx.h>
#pragma hdrstop

#include "Menu.h"
#include <Androidapi.Helpers.hpp> // Para usar JNI
#include <System.SysUtils.hpp> // Para la función Try
#include <Androidapi.JNIBridge.hpp>

#pragma package(smart_init)
#pragma resource "*.fmx"

TFMenu *FMenu;

__fastcall TFMenu::TFMenu(TComponent* Owner)
    : TForm(Owner), jClass(nullptr), jObject(nullptr), methodId(nullptr) // Inicializar los punteros
{
    JNIEnv* env = TJNIResolver::GetJNIEnv();

    const char* jclassName = "com/embarcadero/MySimpleClass";

    try {
        jClass = env->FindClass(jclassName);

        if (jClass == nullptr) {
            throw Exception("Error: Clase Java no encontrada: " + String(jclassName));
        }

        jClass = (jclass)env->NewGlobalRef(jClass); 

        jmethodID constructor = env->GetMethodID(jClass, "<init>", "()V");

        if (constructor == nullptr) {
            throw Exception("Error: Constructor Java no encontrado");
        }

        jObject = env->NewObject(jClass, constructor);

        if (jObject == nullptr) {
            throw Exception("Error: No se pudo crear la instancia de la clase Java");
        }

        jObject = env->NewGlobalRef(jObject); // **¡IMPORTANTE: Referencia Global!**

        methodId = env->GetMethodID(jClass, "savHello", "()V");

        if (methodId == nullptr) {
            throw Exception("Error: Método Java no encontrado");
        }

        env->CallVoidMethod(jObject, methodId);


    } catch (const Exception& e) {
        ShowMessage(e.Message);
        if (jClass) {
            env->DeleteGlobalRef(jClass);
            jClass = nullptr;
        }
        if (jObject) {
            env->DeleteGlobalRef(jObject);
            jObject = nullptr;
        }
        methodId = nullptr;  
    }
}


__fastcall TFMenu::~TFMenu() {
    JNIEnv* env = TJNIResolver::GetJNIEnv();
    if (jClass) {
        env->DeleteGlobalRef(jClass);
    }
    if (jObject) {
        env->DeleteGlobalRef(jObject);
    }
}

I created the MySimpleClass.jar file and  included  in MyProyect/Java/ and  it in my remote path (deployment) “.\library”.

 

My configuration is C++BUILDER 11.1, Android Platform 32 bits, java 1.8, sdk 25, ndk 22;

 

Please, I am very frustrated. Can anyone help me? thank.

Edited March 8 by Drummer1972

[Remy Lebeau 1543]

Why are you putting your Java class in an Embarcadero package?  You should be creating your own package.

 

How does your C++ project refer to your MySimpleClass.jar file? Did you use the Project Manager, or a manual classes.dex file?

 

Have you considered creating a JNI Bridge to your class, instead of manually using JNI methods directly?

 

Using a Custom Set of Java Libraries In Your RAD Studio Android Apps

Creating and Deploying a classes.dex File Manually

Adding A Java Library to Your Application Using the Project Manager

 

Something else to keep in mind (not sure if this applies here):

 

https://stackoverflow.com/a/20843365/65863

Quote

The FindClass method should be called from Java thread only. FindClass's implementation is looking for a ClassLoader by traversing the current call-stack. Since you are trying to call the FindClass from a native thread, there is no ClassLoader to look for. Take a look at this JNI FAQ

 

Edited March 8 by Remy Lebeau