我有以下问题。我想写一个Android应用程序，它使用我的遗产C ++类。我必须保持一个C的整个应用程序生命周期中++对象还活着。

I've got a following problem. I want to write an Android application, which uses my legacy C++ classes. I have to keep a C++ object alive during the whole application lifetime.

我写在C＃中有类似的应用程序，并通过将一个指向一个C ++类，C＃和使用的IntPtr存放在那里解决了这个问题。然后，当我想调用一个方法的对象，我只是再次通过该指针C ++，转换为一个类的指针，并呼吁一个方法就可以了。

I wrote a similar application in C# and solved the problem by passing a pointer to a C++ class to C# and storing it there using IntPtr. Then, when I wanted to call a method on that object, I simply passed that pointer again to C++, converted to a class pointer and called a method on it.

我如何能够实现类似结果的Java和Android NDK？是否支持Java存储指针？

How can I achieve similar result in Java and Android NDK? Does Java support storing pointers?

推荐答案

是的，你可以做的比你在C＃中做了完全一样的。

Yes, you can do the exact same than what you did in C#.

要创建新的C ++对象：

To create your new C++ Object:

jlong
Java_package_name_new(JNIEnv *, jobject) {
  return (long)(new CPP_Object()); 
}

您可以存储这个方法在Java PTR 变量的返回值，并将其传递给所有NDK方法需要它：

You can store the return value of this method in a Java ptr variable, and pass it to all NDK methods that need it:

void
Java_package_name_doSomething(JNIEnv *, jobject, jlong ptr) {
  CPP_Object *obj = (CPP_Object *)ptr;
  // do whatever you want with the object
}

最后删除的东西，如：

And finally delete it with something like:

void
Java_package_name_delete(JNIEnv *, jobject, jlong ptr) {
  delete (CPP_Object *)(ptr);
}

而不是传递 PTR 需要它，你也可以得到它，距离NDK部分采用直接设置它的 SetLongField 和 GetLongField 方法：这允许Java PTR 变量只能从NDK的一部分进行管理的code，我觉得更安全，更易于管理。