cocos2d-x-3.x-026 移植cocos的jnihelper及用法說明

原文地址

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

jni helper源碼

• 來自cocos 3.8, 頭文件
  “`

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 *className,
        const char *methodName, const char *paramCode);

static jmethodID loadclassMethod_methodID;
static jobject classloader;

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

static bool getMethodInfo_DefaultClassLoader(JniMethodInfo &methodinfo,
        const char *className, const char *methodName,
        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裏設置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，參數爲context。在loadLibrary之後，在合適的地方調用該方法
   “`
   public native static int nativeInit(Context context);

在這個native的實現裏，調用JniHelper::setClassLoaderFrom(obj);
jint xxx(JNIEnv* env, jclass clazz, jobject obj) {
JniHelper::setClassLoaderFrom(obj);
return 0;
}

“`

1. 用法舉例
   
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

• 從調用方向看，c call java， cocos的jni絕大部分採用c call 靜態的java方法。原因很明顯，簡單！
• java call c， 沒什麼好說的。