1.在工程目录下创建xxx.jni包并在该包下创建JNI类
2.在JNI类中声明所有的本地方法，并加载库
3.在MainActivity类中实例化JNI对象，并调用其方法
4.通过Javah生成的方法名在对应C文件中进行实现
5.在jni目录下添加Android.mk和Application.mk文件
Demo:
JNI.java：
public class JNI
{
static {
System.loadLibrary("pass_data");
}
public native int add(int x, int y);
public native String string(String str);
public native int [] intArrayElements(int[] array);
}
MainActivity.java:
public class MainActivity extends Activity implements OnClickListener
{
Button bt_int = null;
Button bt_string = null;
Button bt_array = null;
public JNI jni = null;
Context mContext = null;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = this;
jni = new JNI();
bt_int = (Button) findViewById(R.id.bt_int);
bt_string = (Button) findViewById(R.id.bt_string);
bt_array = (Button) findViewById(R.id.bt_array);
bt_int.setOnClickListener(this);
bt_string.setOnClickListener(this);
bt_array.setOnClickListener(this);
} @Override
public void onClick(View v)
{
switch (v.getId())
{
case R.id.bt_int:
Toast.makeText(mContext, jni.add(4, 8) + "", Toast.LENGTH_SHORT).show();
break;
case R.id.bt_string:
Toast.makeText(mContext, jni.string("abcdefg"), Toast.LENGTH_SHORT).show();
break;
case R.id.bt_array:
int [] array = new int[]{1, 2, 3, 4, 5};
jni.intArrayElements(array);
for (int i : array)
{
Log.d("test", i + "");
}
break;
default:
break;
}
}
}
pass_data.c
#include <stdio.h>
#include <stdlib.h>
#include <jni.h>
/*
* Class: com_rocky_passdata_jni_JNI
* Method: add
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_com_rocky_passdata_jni_JNI_add
(JNIEnv *env, jobject clazz, jint x, jint y)
{
return x + y;
}
/**
* 把一个jstring转换成一个c语言的char* 类型.
*/
char* _JString2CStr(JNIEnv* env, jstring jstr) {
char* rtn = NULL;
jclass clsstring = (*env)->FindClass(env, "java/lang/String");
jstring strencode = (*env)->NewStringUTF(env,"GB2312");
jmethodID mid = (*env)->GetMethodID(env, clsstring, "getBytes", "(Ljava/lang/String;)[B");
jbyteArray barr = (jbyteArray)(*env)->CallObjectMethod(env, jstr, mid, strencode); // String .getByte("GB2312");
jsize alen = (*env)->GetArrayLength(env, barr);
jbyte* ba = (*env)->GetByteArrayElements(env, barr, JNI_FALSE);
if(alen > ) {
rtn = (char*)malloc(alen+); //"\0"
memcpy(rtn, ba, alen);
rtn[alen]=;
}
(*env)->ReleaseByteArrayElements(env, barr, ba,);
return rtn;
}
/*
* Class: com_rocky_passdata_jni_JNI
* Method: string
* Signature: (Ljava/lang/String;)Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_rocky_passdata_jni_JNI_string
(JNIEnv *env, jobject clazz, jstring str)
{
char *cstr = _JString2CStr(env, str);
int len = strlen(cstr);
int i;
for (i = ; i < len; i ++)
{
*(cstr + i) += ;
}
return (*env)->NewStringUTF(env, cstr);
}
JNIEXPORT jintArray JNICALL Java_com_rocky_passdata_jni_JNI_intArrayElements
(JNIEnv *env, jobject clazz, jintArray array)
{
int i;
jsize len = (*env)->GetArrayLength(env, array);
int *elements = (*env)->GetIntArrayElements(env, array, NULL);
for (i = ; i < len; i ++)
{
*(elements + i) += ;
}
return array;
}
Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := pass_data
LOCAL_SRC_FILES := pass_data.c
include $(BUILD_SHARED_LIBRARY)
Application.mk
APP_ABI := all
APP_PLATFORM := android-