文章出处:http://blog.csdn.net/shift_wwx
前言:之前的一篇(Android基础总结之九:JNI详解)是结合实例的简单总结,这边总结一下JNINativeMethod。
1、JNINativeMethod 结构体的官方定义
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方法名字示例:
static JNINativeMethod methods[] = { { "printJNI", "()I", (void*)printForTest}, };
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);
2、第二个参数之基本类型
3、第二个参数之对象类型和数组类型
对象类型:以"L"开头,以";"结尾,中间用"/"隔开。如表第一行。
数组类型:以"["开头,如表第二行(n维数组的话,则前面就n个"[",如"[[[D"就表示double[ ][ ][ ])。
对象数组类型:就是上述两者结合,如表第三行。
4、举例
5、结合Media中的看看
static JNINativeMethod gMethods[] = { { "_setDataSource", "(Ljava/lang/String;[Ljava/lang/String;[Ljava/lang/String;)V", (void *)android_media_MediaPlayer_setDataSourceAndHeaders }, {"_setDataSource", "(Ljava/io/FileDescriptor;JJ)V", (void *)android_media_MediaPlayer_setDataSourceFD}, {"_setVideoSurface", "(Landroid/view/Surface;)V", (void *)android_media_MediaPlayer_setVideoSurface}, {"prepare", "()V", (void *)android_media_MediaPlayer_prepare}, {"prepareAsync", "()V", (void *)android_media_MediaPlayer_prepareAsync}, {"_start", "()V", (void *)android_media_MediaPlayer_start}, {"_stop", "()V", (void *)android_media_MediaPlayer_stop}, {"getVideoWidth", "()I", (void *)android_media_MediaPlayer_getVideoWidth}, {"getVideoHeight", "()I", (void *)android_media_MediaPlayer_getVideoHeight}, {"seekTo", "(I)V", (void *)android_media_MediaPlayer_seekTo}, {"_pause", "()V", (void *)android_media_MediaPlayer_pause}, {"isPlaying", "()Z", (void *)android_media_MediaPlayer_isPlaying}, {"getCurrentPosition", "()I", (void *)android_media_MediaPlayer_getCurrentPosition}, {"getDuration", "()I", (void *)android_media_MediaPlayer_getDuration}, {"_release", "()V", (void *)android_media_MediaPlayer_release}, {"_reset", "()V", (void *)android_media_MediaPlayer_reset}, {"setAudioStreamType", "(I)V", (void *)android_media_MediaPlayer_setAudioStreamType}, {"setLooping", "(Z)V", (void *)android_media_MediaPlayer_setLooping}, {"isLooping", "()Z", (void *)android_media_MediaPlayer_isLooping}, {"setVolume", "(FF)V", (void *)android_media_MediaPlayer_setVolume}, {"native_invoke", "(Landroid/os/Parcel;Landroid/os/Parcel;)I",(void *)android_media_MediaPlayer_invoke}, {"native_setMetadataFilter", "(Landroid/os/Parcel;)I", (void *)android_media_MediaPlayer_setMetadataFilter}, {"native_getMetadata", "(ZZLandroid/os/Parcel;)Z", (void *)android_media_MediaPlayer_getMetadata}, {"native_init", "()V", (void *)android_media_MediaPlayer_native_init}, {"native_setup", "(Ljava/lang/Object;)V", (void *)android_media_MediaPlayer_native_setup}, {"native_finalize", "()V", (void *)android_media_MediaPlayer_native_finalize}, {"getAudioSessionId", "()I", (void *)android_media_MediaPlayer_get_audio_session_id}, {"setAudioSessionId", "(I)V", (void *)android_media_MediaPlayer_set_audio_session_id}, {"setAuxEffectSendLevel", "(F)V", (void *)android_media_MediaPlayer_setAuxEffectSendLevel}, {"attachAuxEffect", "(I)V", (void *)android_media_MediaPlayer_attachAuxEffect}, {"native_pullBatteryData", "(Landroid/os/Parcel;)I", (void *)android_media_MediaPlayer_pullBatteryData}, {"setParameter", "(ILandroid/os/Parcel;)Z", (void *)android_media_MediaPlayer_setParameter}, {"getParameter", "(ILandroid/os/Parcel;)V", (void *)android_media_MediaPlayer_getParameter}, {"native_setRetransmitEndpoint", "(Ljava/lang/String;I)I", (void *)android_media_MediaPlayer_setRetransmitEndpoint}, {"setNextMediaPlayer", "(Landroid/media/MediaPlayer;)V", (void *)android_media_MediaPlayer_setNextMediaPlayer}, {"updateProxyConfig", "(Landroid/net/ProxyProperties;)V", (void *)android_media_MediaPlayer_updateProxyConfig}, };如,
{"getParameter", "(ILandroid/os/Parcel;)V", (void *)android_media_MediaPlayer_getParameter},就是代表java层函数void getParameter(int a , Parcel b),返回值是void,形参是init型和Parcel型
{"native_setRetransmitEndpoint", "(Ljava/lang/String;I)I", (void *)android_media_MediaPlayer_setRetransmitEndpoint},就代表java层函数int native_setRetransmitEndpoint(String a, int b),返回值是int,形参是String型和int型