Android的NDK开发(4)————JNI数据结构之JNINativeMethod

1、JNINativeMethod 结构体的官方定义

[cpp]
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typedef struct { 

 
const char* name; 

const char* signature; 

void* fnPtr; 
} JNINativeMethod; 

typedef struct {

const char* name;
const char* signature;
void* fnPtr;
} JNINativeMethod;

第一个变量name是Java中函数的名字。

第二个变量signature，用字符串是描述了Java中函数的参数和返回值

第三个变量fnPtr是函数指针，指向native函数。前面都要接
(void *)

第一个变量与第三个变量是对应的，一个是java层方法名，对应着第三个参数的native方法名字

更多内容请查看之前博文：http://blog.csdn.net/conowen/article/details/7521340

示例：

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/*
* 由于gMethods[]是一个<名称，函数指针>对照表，在程序执行时，
* 可多次调用registerNativeMethods()函数来更换本地函数的指针，

* 从而达到弹性调用本地函数的目的。 
*具体可以参看http://blog.csdn.net/conowen/article/details/7521340

*/   
static JNINativeMethod gMethods[] = {   

    {"setDataSource",       "(Ljava/lang/String;)V",            (void *)com_media_ffmpeg_FFMpegPlayer_setDataSource},   

    {"_setVideoSurface",   
"(Landroid/view/Surface;)V",        (void *)com_media_ffmpeg_FFMpegPlayer_setVideoSurface},   

    {"prepare",             "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_prepare},   

    {"_start",             
"()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_start},   

    {"_stop",               "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_stop},   

    {"getVideoWidth",      
"()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getVideoWidth},   

    {"getVideoHeight",      "()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getVideoHeight},   

    {"seekTo",             
"(I)V",                             (void *)com_media_ffmpeg_FFMpegPlayer_seekTo},   

    {"_pause",              "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_pause},   

    {"isPlaying",          
"()Z",                              (void *)com_media_ffmpeg_FFMpegPlayer_isPlaying},   

    {"getCurrentPosition",  "()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getCurrentPosition},   

    {"getDuration",        
"()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getDuration},   

    {"_release",            "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_release},   

    {"_reset",             
"()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_reset},   

    {"setAudioStreamType",  "(I)V",                             (void *)com_media_ffmpeg_FFMpegPlayer_setAudioStreamType},   

    {"native_init",        
"()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_native_init},   

    {"native_setup",        "(Ljava/lang/Object;)V",            (void *)com_media_ffmpeg_FFMpegPlayer_native_setup},   

    {"native_finalize",    
"()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_native_finalize},   

    {"native_suspend_resume",
"(Z)I",                           (void *)com_media_ffmpeg_FFMpegPlayer_native_suspend_resume},   

};   
   

/*
* 由于gMethods[]是一个<名称，函数指针>对照表，在程序执行时，
* 可多次调用registerNativeMethods()函数来更换本地函数的指针，
* 从而达到弹性调用本地函数的目的。
*具体可以参看http://blog.csdn.net/conowen/article/details/7521340
*/
static JNINativeMethod gMethods[] = {
{"setDataSource",       "(Ljava/lang/String;)V",            (void *)com_media_ffmpeg_FFMpegPlayer_setDataSource},
{"_setVideoSurface",    "(Landroid/view/Surface;)V",        (void *)com_media_ffmpeg_FFMpegPlayer_setVideoSurface},
{"prepare",             "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_prepare},
{"_start",              "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_start},
{"_stop",               "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_stop},
{"getVideoWidth",       "()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getVideoWidth},
{"getVideoHeight",      "()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getVideoHeight},
{"seekTo",              "(I)V",                             (void *)com_media_ffmpeg_FFMpegPlayer_seekTo},
{"_pause",              "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_pause},
{"isPlaying",           "()Z",                              (void *)com_media_ffmpeg_FFMpegPlayer_isPlaying},
{"getCurrentPosition",  "()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getCurrentPosition},
{"getDuration",         "()I",                              (void *)com_media_ffmpeg_FFMpegPlayer_getDuration},
{"_release",            "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_release},
{"_reset",              "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_reset},
{"setAudioStreamType",  "(I)V",                             (void *)com_media_ffmpeg_FFMpegPlayer_setAudioStreamType},
{"native_init",         "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_native_init},
{"native_setup",        "(Ljava/lang/Object;)V",            (void *)com_media_ffmpeg_FFMpegPlayer_native_setup},
{"native_finalize",     "()V",                              (void *)com_media_ffmpeg_FFMpegPlayer_native_finalize},
{"native_suspend_resume", "(Z)I",                           (void *)com_media_ffmpeg_FFMpegPlayer_native_suspend_resume},
};

主要是第二个参数比较复杂：

括号里面表示参数的类型，括号后面表示返回值。

"()" 中的字符表示参数，后面的则代表返回值。例如"()V" 就表示void Fun();

"(II)V" 表示 void Fun(int a, int b);

这些字符与函数的参数类型的映射表如下：

2、第二个参数之基本数据类型



3、第二个参数之对象类型与数组类型



对象类型：以"L"开头，以";"结尾，中间是用"/" 隔开。如上表第1个

数组类型：以"["开始。如上表第2个（n维数组的话，则是前面多少个"["而已，如"[[[D"表示“double[][][]”）

对象数组类型：上述两者结合，如上表第3个

3.1、对象类型与数组类型的举例：