通过JNI将C ++类返回到Java [英] Returning a C++ class to Java via JNI

问题描述

我目前在项目中使用C ++和Java，我想能够将包含在C ++中的对象发送到我的Java接口，以便通过GUI修改它，然后将修改发回在C ++中。

到目前为止，我已经通过JNI接口向Java返回了任何内容，一个int或一个布尔值。这一次我必须通过接口发送一个对象。我已经在C ++和Java中提供类似的类定义。 我想知道如何创建对象，以便我可以在Java中使用它。

在C ++中：

  JNIEXPORT MyObject JNICALL Java_ca_X_Y_Z_C_1getMyObject（JNIEnv * env，jclass，jint number）; 
  

此函数将被Java调用，以便从C ++端获取对象包含在单例中，容易访问）。

在Java端，我对这个方法进行一个简单的调用，

  MyObject anObject = C_getMyObject（3）; 
  

应返回新创建的对象。

当我进行实际调用时，Java目前返回一个UnsatisfiedLinkError。

解决方案

这里是我选择使用的解决方案：

<首先，我将在Java中创建一个类似的对象。然后，从C ++我会把它传递给它，并传递所有的值。

 （C ++）
 clazz = env- > FindClass（java / lang / Integer）; 
 jmethodID method = env-> GetMethodID（clazz，< init>，（I）V）; 
 return env-> NewObject（clazz，method，（jint）anInteger）; 
  

但是我意识到这不是很便携，有点太复杂了。

相反，我决定返回一个字符串，Java会解析并使用它来初始化对象。

 （JAVA）
 String aString =valuesoftheobject; 
 MyObject myObject（aString）; 
  

MyObject将有一个构造函数接受一个字符串。我相信解决方案简单有效。

I'm currently using both C++ and Java in a project and I'd like to be able to send an object which is contained in C++ to my Java interface in order to modify it via a GUI and then send the modification back in C++.

So far I've been returning either nothing, an int or a boolean to Java via the JNI interface. This time I have to send an object through the interface. I have made similar class definition available both in C++ and in Java. I'd like to know how I'd go about creating the object so that I can use it in Java.

In C++ I have:

JNIEXPORT MyObject JNICALL Java_ca_X_Y_Z_C_1getMyObject(JNIEnv* env, jclass, jint number);

This function would get called by Java in order to get the object from the C++ side (the object is contained in a singleton, easily accessible).

On the Java end, I do a simple call to this method,

MyObject anObject = C_getMyObject(3);

which should return me the newly created object.

Java currently returns me a UnsatisfiedLinkError when I do the actual call. What is wrong?

解决方案

Here's the solution I opted to use:

First, I would create a similar object in Java. Then, from C++ I would instanciate it and pass it all the values.

(C++)
clazz = env->FindClass("java/lang/Integer");
jmethodID method = env->GetMethodID(clazz, "<init>", "(I)V");
return env->NewObject(clazz, method, (jint)anInteger);

But then I realised this wasn't very portable and was a bit too complicated.

Instead, I decided to return a string that Java would parse and use to initialize the object on its side.

(JAVA)
String aString = "valuesoftheobject";
MyObject myObject(aString);

MyObject would have a constructor which takes a string. I believe the solution is simple and effective.

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