【系统移植】JNI

jni代码

java调用jni的接口:

1, 调用动态库

static{
 
  System.loadLibrary("led_jni");  // system/lib/libled_jni.so
 }

2, 调用驱动方法名:
    public native int openDev();
  
3, 直接去调用,不需要去实现openDev()

openDev();
 public native int openDev();
 public native int DevOn();
 public native int DevOff();
 public native int closeDev();

jni的接口代码: jni代码(*.cpp)==>libled_jni.so

参考模板:Native.cpp developmentsamplessimplejniJni 2599 2011-5-17

1, JNI_OnLoad()   <== System.loadLibrary("led_jni") 第一个函数
 |
 原型:jint JNI_OnLoad(JavaVM* vm, void* reserved)
  返回值: 正确: JNI_VERSION_1_4
   错误: 小于0;
 a, 获取jni的版本,和dvm的运行环境对象 env (提供操作jni的方法)
  原型:  jint GetEnv(void** env, jint version)
  使用:   
    JNIEnv* env = NULL;
   vm->GetEnv((void **)&env, JNI_VERSION_1_4) 
   返回值:
    正确: JNI_OK == 0
    错误: 小于0
   
 b, 构建映射表, 注册给dvm
  表示映射表:
  typedef struct { 
      const char* name;   // java方法名
      const char* signature;  // 方法的参数和返回值 描述
      void*       fnPtr; // c/c++的函数名
  } JNINativeMethod;
  const static JNINativeMethod   myMethods[] ={
   {"openDev", "()I", (void *)open_led},
   {"DevOn", "()I",   (void *)led_on},
   {"DevOff", "()I",  (void *)led_off},
   {"closeDev", "()I", (void *)close_led},
  };

  注册:
   env->RegisterNatives(jclass clazz, const JNINativeMethod* methods,jint nMethods)
   参数1: 将native方法所在的包.类转换成jclass, 告诉dvm,本地方法是属于哪个类
   jclass  myclz = env->FindClass("com/hq/ledjnitest/LedActivity");

   env->RegisterNatives(myclz, myMethods,   sizeof(myMethods)/sizeof(myMethods[0]));

Android.mk

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= led_jni.cpp
LOCAL_MODULE :=libled_jni

#指定连接动态库< 类似于gcc  -lxx
LOCAL_SHARED_LIBRARIES :=
        libcutils
#指定头文件路径, 类似于gcc -Ixxx
LOCAL_C_INCLUDES +=
        $(JNI_H_INCLUDE)
#编译成so,需要一个标志
LOCAL_PRELINK_MODULE := false
include $(BUILD_SHARED_LIBRARY)

编译:

mmm mytest/jni/
============================================
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=2.1-update1
TARGET_PRODUCT=fs100
TARGET_BUILD_VARIANT=eng
TARGET_SIMULATOR=false
TARGET_BUILD_TYPE=release
TARGET_ARCH=arm
HOST_ARCH=x86
HOST_OS=linux
HOST_BUILD_TYPE=release
BUILD_ID=ERE27
============================================
make:进入目录'/home/ldswfun/src_s5pc/eclair_2.1_farsight'
target thumb C++: libled_jni <= mytest/jni/led_jni.cpp
In file included from mytest/jni/led_jni.cpp:5:
dalvik/libnativehelper/include/nativehelper/jni.h:489: note: the mangling of 'va_list' has changed in GCC 4.4
target SharedLib: libled_jni (out/target/product/fs100/obj/SHARED_LIBRARIES/libled_jni_intermediates/LINKED/libled_jni.so)
target Non-prelinked: libled_jni (out/target/product/fs100/symbols/system/lib/libled_jni.so)
target Strip: libled_jni (out/target/product/fs100/obj/lib/libled_jni.so)
Install: out/target/product/fs100/system/lib/libled_jni.so
make:离开目录“/home/ldswfun/src_s5pc/eclair_2.1_farsight”

运行:

apk===> /system/app
so ==> /syste/lib/
cp -raf out/target/product/fs100/system/lib/libled_jni.so   /opt/myrootfs/system/lib

 @成鹏致远

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