初识JNI（一）

JNI是Android的重要组成部分，它帮助我们解决了2件事。

1.JAVA函数可以直接调用native语言写的函数，一般指的是C，C++函数

2.native语言C,C++的函数可以调用java的函数，

总结，JNI是Native世界和JAVA世界的桥梁。

我们可能会接触到这样的类。

package com.vss.vssmobile.common;import com.vss.vssmobile.entity.DeviceInfo;import com.vss.vssmobile.entity.DirInfo;import com.vss.vssmobile.listener.IORecvListener;public class Zlvss {private Zlvss() {}private static final Zlvss zlvss = new Zlvss();public static Zlvss getInstance() {return zlvss;};static {try {System.loadLibrary("item1");System.loadLibrary("item2");} catch (UnsatisfiedLinkError ule) {System.out.println("loadLibrary(API)," + ule.getMessage());}}public native void sharedInstance();public native void destroyInstance();public native void setonRecvListener(IORecvListener i);public native void  clearRecvListener();public native int p2pserver_sdk_init(); // uselesspublic native int return_p2pserver_status();public native int p2pserver_reconnect();public native int devmanager_get_devID_fromDeviceInfo(DeviceInfo info);public native DeviceInfo devmanager_get_devInfo_fromDevID(int devid);public native int devmanager_get_videoID_fromDevID(int devid, int chnnum);public native int devmanager_isConnectMainToDevice(int devid);public native int devmanager_isConnectSubToDevice(int devid);public native int devmanager_isConnectVideoToDevice(int devid, int chnnum);public native boolean devmanager_test_mainIsConnected(int devid);public native boolean devmanager_get_main_isProxy(int devid);public native boolean devmanager_get_sub_isProxy(int devid);public native boolean devmanager_get_video_isProxy(int devid, int num);public native int devmanager_addDevice_deviceInfo(DeviceInfo info);public native int devmanager_createDevice_deviceInfo(DeviceInfo info);public native void devmanager_deleteDevice_devID(int devid);public native int devmanager_loginToDevice_devID(int devid);public native boolean devmanager_setDevice_devID(int devid, int chnnum);public native void devmanager_logoutFromDevice_devID(int devid);public native int devmanager_checkUserLimitFromDevice_devID(int devid);public native int devmanager_connectVideoToDevice_devID(int devid, int num);public native void devmanager_disconnectVideoFromDevice_devID(int devid,int num);public native int devmanager_requestVideoFromDevice_devID(int devid,int num, int issub);public native int devmanager_stopVideoFromDevice_devID(int devid, int num,int issub);public native long devmanager_getVideoDataFlow_devID(int devid);public native int devmanager_startRecord_devID(int devid, int num,String path);public native void devmanager_stopRecord_devID(int devid, int num);public native int devmanager_openAlarmToDevice_devID(int devid,int num,int type);public native int devmanager_closeAlarmToDevice_devID(int devid,int num,int type);public native void  devmanager_ptzControl_devID (int devid,int num,int type);public native int devmanager_remoteKeyboard_devID(int devid, int btnid);public native int devmanager_connectSubToDevice_devID(int devid);public native int devmanager_disconnectSubFromDevice_devID(int devid);public native int playback_searchVideoFile_devID(int devid,int num,int year,int month,int day,int hour,int min,int second);public  native  int playback_searchDownloadVideoFile_devID(int devid,int num,int year1,int month1,int day1,int hour1,int min1,int second1,int year2,int month2,int day2,int hour2,int min2,int sencond2);public native int playback_requestVideoFile_devID(int devid, int num,int  position);public native int playback_requestDownloadVideoFile_devID(int devid,int num, DirInfo c);public native int playback_stopVideoFile_devID(int devid, int num);public native void playback_pauseVideoFile_devID(int devid);public native void playback_continueVideoFile_devID(int devid);public native void playback_quickPlayVideoFile_devID(int devid);public native void playback_slowPlayVideoFile_devID(int devid);public native void playback_playVideoFile_devID(int devid, int num,int c, double percent);public native int playback_startRecord_devID(int devid, String path);public native void playback_stopRecord_devID(int devid);public native int  zeroVideo_requestZeroVideo_devID (int devid,int param1,int param2);public native int  zeroVideo_stopZeroVideo_devID(int devid);}

一上手，一堆的native方法。但他又不是接口类型的，这样的话，它是怎么调用的呢，首先你可以安卓项目的libs库里找到libitem1.so和libitem2.so类似的文件，这个就是动态库，Linux以so为后缀名，

这样就找到了native世界和JAVA世界2边程序员需要做的事。 JAVA程序员根据需求编写如上文件，在实际的应用场景来调用这些native函数。

然后native层C,C++程序员做具体的实现。

tips: so文件一般以lib+名称+.so命名。如libitem1.so.

其次必须准确的规范JAVA层的输入参数和返回类型，不然可能需要重新编译。

JAVA在这个类加载的时候，会加载到static 代码，里面加载了2个so。不然你无法找到Native函数的具体实现。

但这个native函数是如何对应C，C++层的具体实现的呢。

有静态注册和动态注册2种。下篇再说。。。