[英]How to call Java API's from Native C/C++ in Android
There are lot of examples that Android C/C++ native calls Java APIs. Android C / C ++本机调用Java API有很多例子。 However, all of these examples I have read are the Android Java APIs call native first and then the native calls other Java APIs by using the passed JNI-ENV.
但是,我读过的所有这些示例都是Android Java API首先调用本机,然后本机通过使用传递的JNI-ENV调用其他Java API。
Without the passed JNI-ENV, how can the C/C++ get it? 没有通过的JNI-ENV,C / C ++怎么能得到它? Is it possible that C/C++ native calls Java APIs in Android by creating JavaVM ?If so please share the links.
C / C ++本机是否有可能通过创建JavaVM来调用Android中的Java API?如果是这样,请分享链接。 I have gone through the one project CoCos2dx which iam unable to find clear details.
我已经完成了一个项目CoCos2dx,我无法找到明确的细节。 github.com/nokia-developer/cocos2d-x-qt/tree/master/
github.com/nokia-developer/cocos2d-x-qt/tree/master/
Thanks in advance! 提前致谢!
Here's how I do it. 这是我如何做到的。 I found out how by referring to The Java Native Interface by Sheng Liang;
我找到了如何通过参考盛良的Java Native Interface ; see page 96. I have a class called ThreadEnv that owns a JNIEnv pointer for the current thread and creates it when it's first needed:
请参阅第96页。我有一个名为ThreadEnv的类,它拥有当前线程的JNIEnv指针,并在首次需要时创建它:
class ThreadEnv
{
public:
JNIEnv* GetEnv()
{
if (m_env == nullptr)
#if defined(ANDROID) || defined(__ANDROID__)
TheJvm->AttachCurrentThread(&m_env,nullptr);
#else
TheJvm->AttachCurrentThread((void**)&m_env,nullptr);
#endif
return m_env;
}
~ThreadEnv()
{
if (m_env)
TheJvm->DetachCurrentThread();
}
private:
JNIEnv* m_env = nullptr;
};
I then use it by making a ThreadEnv object a member of any C++ class that needs it in my JNI code, and calling GetEnv to get the JNIEnv pointer. 然后我通过使ThreadEnv对象成为我的JNI代码中需要它的任何C ++类的成员,并调用GetEnv来获取JNIEnv指针来使用它。 Here's an example of how I use it in one of my classes: take a look at the OnChange member function.
以下是我在其中一个类中使用它的示例:查看OnChange成员函数。
class MyFrameworkObserver: public MFrameworkObserver, public MUserData
{
public:
MyFrameworkObserver(jobject aFrameworkObject): m_framework_object(aFrameworkObject) { }
~MyFrameworkObserver()
{
JNIEnv* env = m_thread_env.GetEnv();
if (env)
env->DeleteGlobalRef(m_framework_object);
}
private:
void OnViewChange() override { OnChange(TheFrameworkOnViewChangeMethodId); }
void OnMainDataChange() override { OnChange(TheFrameworkOnMainDataChangeMethodId); }
void OnDynamicDataChange() override { OnChange(TheFrameworkOnDynamicDataChangeMethodId); }
void OnChange(jmethodID aMethodID)
{
JNIEnv* env = m_thread_env.GetEnv();
if (env)
env->CallVoidMethod(m_framework_object,aMethodID);
}
jobject m_framework_object;
ThreadEnv m_thread_env;
};
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