如何通过Java类的实例作为参数传递给JNI方法? [英] how to pass java class instance as a parameter to JNI method?
问题描述
我想java类对象传递给JNI方法,
我想调用JNI方法几个方法如下图所示。
是否有任何人谁拥有像下面的一些例子吗?
类JavaClassParameter {
无效javaMethodTobeCalledInJNI(){
... java源...
}
}类MainJavaClass {
无效的someMethod(){
JavaClassParameter对象=新JavaClassParameter();
JNIMethod(对象);
} 本地无效JNIMethod(JavaClassParameter对象);
}
// C ++ code
无效JNIMethod(对象){
对象 - > javaMethodTobeCalledInJNI();
}
您的方法声明:
类MainJavaClass {
本地无效JNIMethod(JavaClassParameter对象);
}
应产生一个向前声明如下所示:
JNIEXPORT无效JNICALL Java_MainJavaClass_JNIMethod(JNIEnv的* ENV,jobject mainJavaClass);
在那的实施,你有几件事要做:
查找JavaClassParameter
使用的findClass
,它需要一个字符串名称:
JCLASS CLS = env->的findClass(JavaClassParameter);
查找javaMethodTobeCalledInJNI()
使用的GetMethodID
,这需要该类检查,该方法的字符串名称,及其签名。由于这是一个无参数的void函数,它的签名一>就是()V
:
jmethodID方法= env->的GetMethodID(CLS,javaMethodTobeCalledInJNI,()V);
呼叫javaMethodTobeCalledInJNI()
使用 CallVoidMethod
,这需要对象实例的方法ID,和任何参数(没有在这种情况下):
env-> CallVoidMethod(mainJavaClass,法);
您应该检查每个步骤后空的结果;如果从一个JNI函数得到一个空回来,把它传递给另外一个,你通常会崩溃JVM
I'd like to pass java class object to JNI method, And I want to call few methods in JNI method like below.
Is there anyone who have some example like below?
class JavaClassParameter{
void javaMethodTobeCalledInJNI(){
...java source...
}
}
class MainJavaClass{
void somemethod(){
JavaClassParameter object = new JavaClassParameter();
JNIMethod(object);
}
native void JNIMethod(JavaClassParameter object);
}
// C++ code
void JNIMethod(object){
object->javaMethodTobeCalledInJNI();
}
Your method declaration:
class MainJavaClass {
native void JNIMethod(JavaClassParameter object);
}
means javah should generate a forward declaration like the following:
JNIEXPORT void JNICALL Java_MainJavaClass_JNIMethod(JNIEnv* env, jobject mainJavaClass);
In the implementation of that, you have a few things to do:
Find JavaClassParameter
Use FindClass
, which takes a string name:
jclass cls = env->FindClass("JavaClassParameter");
Find javaMethodTobeCalledInJNI()
Use GetMethodID
, which takes the class to check, the string name of the method, and its signature. Since this is a void function with no arguments, its signature is just ()V
:
jmethodID method = env->GetMethodID(cls, "javaMethodTobeCalledInJNI", "()V");
Call javaMethodTobeCalledInJNI()
Use CallVoidMethod
, which takes the object instance, the method ID, and any arguments (none in this case):
env->CallVoidMethod(mainJavaClass, method);
You should check for NULL results after each step; if you get a NULL back from one JNI function and pass it to another, you'll usually crash the JVM
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