原文地址

• https://github.com/cheyiliu/All-in-One/wiki/Cocos2d-x

jni Helper源码

• 来自cocos 3.8,头文件
  “`

ifndef ANDROID_JNI_HelPER_H

define ANDROID_JNI_HelPER_H

include

include

typedef struct JniMethodInfo_ {
JNIEnv * env;
jclass classID;
jmethodID methodID;
} JniMethodInfo;

class JniHelper {
public:
static void setJavaVM(JavaVM *javaVM);
static JavaVM* getJavaVM();
static JNIEnv* getEnv();

static bool setClassLoaderFrom(jobject activityInstancE);
static bool getStaticMethodInfo(JniMethodInfo &methodinfo,const char *className,const char *methodName,const char *paramCodE);
static bool getMethodInfo(JniMethodInfo &methodinfo,const char *paramCodE);

static jmethodID loadclassMethod_methodID;
static jobject classloader;

private:
static JNIEnv* cacheEnv(JavaVM* jvm);

static bool getMethodInfo_DefaultClassLoader(JniMethodInfo &methodinfo,const char *paramCodE);

static JavaVM* _psJavaVM;

};

endif // ANDROID_JNI_HelPER_H

“`

• .cpp
  “`

include “JniHelper.h”

include “dlog.h”

include

include

include

用法

1. 在jni onload里设置jvm
   “`

JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm,void* reserved) {
// other code
// …

JniHelper::setJavaVM(vm);
return JNI_VERSION_1_4;

}
“`

1. 在java新增一native方法，参数为context。在loadLibrary之后，在合适的地方调用该方法
   “`
   public native static int nativeInit(Context context);

在这个native的实现里，调用JniHelper::setClassLoaderFrom(obj);
jint xxx(JNIEnv* env,jclass clazz,jobject obj) {
JniHelper::setClassLoaderFrom(obj);
return 0;
}

“`

1. 用法举例
   
int getDPIJNI()
{
JniMethodInfo t;
jint ret = -1;
if (JniHelper::getStaticMethodInfo(t,"org/cocos2dx/lib/Cocos2dxHelper","getDPI","()I")) {
ret = t.env->CallStaticIntMethod(t.classID,t.methodID);
t.env->deleteLocalRef(t.classID);
}
return ret;
}


其他

• 从调用方向看，c call java， cocos的jni绝大部分采用c call 静态的java方法。原因很明显，简单！
• java call c， 没什么好说的。