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

1、JNINativeMethod 结构体的官方定义

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：

/*
 * 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：

1、JNINativeMethod 结构体的官方定义

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：

/*
 * 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：