android jni 程序框架搭建

android上 jni开发应用构建过程基本一致，下面结合最近在android 上实现 jni层绘制 surfaceview 功能阐述带jni的apk构建过程。

apk 目录结构：

├── AndroidManifest.xml├── Android.mk├── jni│   ├── Android.mk│   ├── logger.cpp│   ├── logger.h│   ├── OnLoad.cpp│   └── SurfaceviewJni.cpp├── libs│   └── armeabi│       └── libsurfaceviewJni.so├── res│   ├── layout│   │   └── hello_activity.xml│   └── values│       └── strings.xml└── src    └── com        └── example            └── android                └── jnisurfaceview                    ├── JavasurfaceView.java                    └── JniSurfaceViewActivity.java

1. java类中 static 块加载动态库及java层本地方法声明：

static {

System.loadLibrary("surfaceviewJni");
}

private native void nativeSetSurface(Surface surface);
private native void nativeDraw(String path ,int width, int height);

2 . 编写 jni makefile

jni/Android.mk

#lib for jnisurfaceviewLOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_LDLIBS := \        -lm -lstdc++ -lgcc -llogLOCAL_SRC_FILES := \OnLoad.cpp \SurfaceviewJni.cpp \                logger.cpp#LOCAL_SHARED_LIBRARIES := libsurfaceviewJniLOCAL_SYSTEM_SHARED_LIBRARIES := libc libstdc++ libutils LOCAL_MODULE := libsurfaceviewJniinclude $(BUILD_SHARED_LIBRARY)

3. 编写 apk makefile

LOCAL_PATH:= $(call my-dir)include $(CLEAR_VARS)# Only compile source java files in this apk.LOCAL_SRC_FILES := $(call all-java-files-under, src)LOCAL_PACKAGE_NAME := JniSurfaceView#LOCAL_JNI_SHARED_LIBRARIES := libsurfaceviewJni#LOCAL_PRELINK_MODULE := falseinclude $(BUILD_PACKAGE)

4. C/C++代码中绑定java层和本地接口

这里的关键点在 JNI_OnLoad 函数，java层在 load 动态库时虚拟机会首先调用动态库中的JNI_OnLoad，所以 java层接口和本地接口的绑定在JNI_OnLoad 函数中初始化即可，这也是android framework 的做法。

放在一个文件中：

OnLoad.cpp

/* * Desc: jni code for surfaceview * Author :lidp */ #include #include #include "logger.h"#define TAG_JNISURFACEVIEW "jni surfaceview test"static JavaVM *jvm = NULL;int register_jnisurfaceview(JNIEnv* env);JNJEnv* getEnv(){JNIEnv* env = NULL;if(jvm->GetEnv(void**)&env, JNI_VERSION_1_4) != JNI_OK) {return NULL;droid_log(LOG_ERROR,"failed in get jvm\n");}return env;}//this function will be called by jvm on load shared libjint JNI_OnLoad(JavaVM *vm,void* reserved){JNIEnv* env = NULL;jint ret = JNI_ERR;droid_log(LOG_DEBUG,"Jni Onload be called\n");jvm = vm;if(jvm->GetEnv((void**)&env, JNI_VERSION_1_4) != JNI_OK) {droid_log(LOG_ERROR,"failed get jvm\n");return ret;}if(register_jnisurfaceview(env) != JNI_OK)return ret;;return JNI_VERSION_1_4;}

5. 实现接口代码：

SurfaceviewJni.cpp

#include #include #include #include #include "logger.h"#include struct JavaGule {jobject jsurface;};static struct JavaGule gule;//code pase from framework jnihelp.cppstatic int jniRegisterNativeMethods(JNIEnv* env, const char* className, const JNINativeMethod* gMethods, int numMethods){    jclass clazz;droid_log(LOG_DEBUG, "register native method for class %s\n", className);    clazz = env->FindClass(className);    if (clazz == NULL)        return -1;    if (env->RegisterNatives(clazz, gMethods, numMethods) < 0)        return -1;    return 0;}static void jnisurfaceview_draw(JNIEnv *env, jobject obj, jstring photopath, jint w, jint h){droid_log(LOG_DEBUG, "native draw be called \n");jclass sufaceClass = env->FindClass("android/view/Surface");if(sufaceClass == NULL) {droid_log(LOG_ERROR,"Cant not find android/view/Surface class\n");return;}jfieldID surfaceID = env->GetFieldID(sufaceClass, "mSurface", "I");    if (surfaceID == NULL) {        droid_log(LOG_ERROR,"Can't find Surface.mSurface");        return;    }//sp surface = (Surface *)env->GetIntField(gule.jsurface, surfaceID);/*if(surface.isValid()) {} else {droid_log(LOG_ERROR, "cant get surface\n");}*/}static void jnisurfaceview_setSurface(JNIEnv *env, jobject obj, jobject javasurface){droid_log(LOG_DEBUG, "native setSurface be called \n");gule.jsurface = javasurface;}static JNINativeMethod gmethods[] = {{"nativeDraw", "(Ljava/lang/String;II)V", (void *)jnisurfaceview_draw},{"nativeSetSurface", "(Landroid/view/Surface;)V", (void*)jnisurfaceview_setSurface},};int register_jnisurfaceview(JNIEnv* env){return jniRegisterNativeMethods(env,"com/example/android/jnisurfaceview/JavasurfaceView", gmethods, sizeof(gmethods)/sizeof(gmethods[0]));}

6. ndk_build 编译 jni目录，生成动态库到 libs目录，

apk 根目录执行 mm 生成apk.

注意：

这里本地代码用到了 ndk提供的log 接口 android/log.h 所以在makefile中要连接log动态库用参数

LOCAL_LDLIBS := \        -lm -lstdc++ -lgcc -llog

上面的 c++代码即包含 java->c++的调用也包含 C++ -> java的反调用。

ok.

csdn lidp 原创，转载著名出处,谢谢。

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