03_Android NDK中C语言调用Java代码，javah的使用，javap的使用以及生成签名，Android.mk的编写，C代码的编写

public class DataProvider {

//C调用java空方法

public void helloFromJava(){

System.out.println("哈哈哈  我被调用了");

}

//C调用java中的带两个int参数的方法

public int Add(int x,int y){

int result=x+y;

System.out.println("result:"+result);

return result;

}

//C调用java中参数为string的方法

public void printString(String s) {

System.out.println(s);

}

public static void demo(){

System.out.println("哈哈哈,我是静态方法");

}

public native void callMethod1();

public native void callMethod2();

public native void callMethod3();

public native void callMethod4();

public native void callMethod5();

}

import android.os.Bundle;

import android.support.v7.app.ActionBarActivity;

import android.view.View;

public class MainActivity extends ActionBarActivity {

DataProvider dp;

static {

System.loadLibrary("hello");

}

public void helloFromJava() {

System.out.print("哈哈哈，我被调用了");

}

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

dp = new DataProvider();

}

public void click1(View view){

dp.callMethod1();

}

public void click2(View view){

dp.callMethod2();

}

public void click3(View view){

dp.callMethod3();

}

public void click4(View view){

dp.callMethod4();

}

public void click5(View view){

dp.callMethod5();

}

}

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context=".MainActivity" >

<Button

android:onClick="click1"

android:id="@+id/button1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_alignParentTop="true"

android:text="回调java中helloFromJava" />

<Button

android:onClick="click2"

android:id="@+id/button2"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_below="@+id/button1"

android:text="回调java中Add" />

<Button

android:onClick="click3"

android:id="@+id/button3"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_below="@+id/button2"

android:text="回调java中PrintString" />

<Button

android:onClick="click4"

android:id="@+id/button4"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_below="@+id/button3"

android:text="回调java中其它类的方法" />

<Button

android:onClick="click5"

android:id="@+id/button5"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_below="@+id/button4"

android:text="回调java中静态的方法" />

</RelativeLayout>

/**

* 调用：DataProvider中的 public void helloFromJava();

*/

JNIEXPORT void JNICALL Java_com_example_ndkcallback_DataProvider_callMethod1

(JNIEnv *env, jobject jobject) {

/**

* Class<?> forName = Class.forName("com.example.ndkcallback.DataProvider");

* Method declaredMethod = forName.getDeclaredMethod("helloFromJava", new Class[]{});

* declaredMethod.invoke(forName.newInstance(), new Object[]{});

*/

//jclass      (*FindClass)(JNIEnv*, const char*);

jclass clazz = (*env)->FindClass(env,"com/example/ndkcallback/DataProvider");

//jmethodID (*GetMethodID)(JNIEnv*,jclass,const char*,const char*)

//方法签名   参数和返回值

//GetMethodID中参数分别是env指针，class，方法名，方法签名

jmethodID methodId=(*env)->GetMethodID(env,clazz,"helloFromJava","()V");

//通过 void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);来调用Java的代码

(*env)->CallVoidMethod(env,jobject,methodId);

}

/**

* 调用：DataProvider中的 public int Add(int, int);

*/

JNIEXPORT void JNICALL Java_com_example_ndkcallback_DataProvider_callMethod2

(JNIEnv *env, jobject jobject) {

jclass clazz=(*env)->FindClass(env,"com/example/ndkcallback/DataProvider");

//这里的方法签名中有几个I表示有几个参数

jmethodID methodId=(*env)->GetMethodID(env,clazz,"Add","(II)I");

// jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);

(*env)->CallIntMethod(env,jobject,methodId,3,5);

}

/**

* 调用：DataProvider中的 public void printString(java.lang.String);

*/

JNIEXPORT void JNICALL Java_com_example_ndkcallback_DataProvider_callMethod3

(JNIEnv *env, jobject jobject) { // 参数 object  就是native方法所在的类

jclass clazz=(*env)->FindClass(env,"com/example/ndkcallback/DataProvider");

jmethodID methodId=(*env)->GetMethodID(env,clazz,"printString","(Ljava/lang/String;)V");

// jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);

jstring str=(*env)->NewStringUTF(env,"hello");

(*env)->CallVoidMethod(env,jobject,methodId,str);

}

JNIEXPORT void JNICALL Java_com_example_ndkcallback_DataProvider_callMethod4

(JNIEnv * env, jobject j){

jclass clazz=(*env)->FindClass(env,"com/example/ndkcallback/MainActivity");

//  jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);

// 方法签名  参数和返回值

jmethodID methodId=(*env)->GetMethodID(env,clazz,"helloFromJava","()V");

// void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);

// 需要创建DataProvider的 对象

// jobject     (*AllocObject)(JNIEnv*, jclass);

jobject obj=(*env)->AllocObject(env,clazz);  // new MainActivity();

(*env)->CallVoidMethod(env,obj,methodId);

}

JNIEXPORT void JNICALL Java_com_example_ndkcallback_DataProvider_callMethod5

(JNIEnv * env, jobject j){

jclass clazz=(*env)->FindClass(env,"com/example/ndkcallback/DataProvider");

//     jmethodID   (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);

jmethodID  methodid=(*env)->GetStaticMethodID(env,clazz,"demo","()V");

//void        (*CallStaticVoidMethod)(JNIEnv*, jclass, jmethodID, ...);

(*env)->CallStaticVoidMethod(env,clazz,methodid);

}

include $(CLEAR_VARS)

LOCAL_MODULE    := libhello

LOCAL_SRC_FILES := Hello.c

include $(BUILD_SHARED_LIBRARY)

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="com.example.ndkcallback"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk

android:minSdkVersion="8"

android:targetSdkVersion="19" />

<application

android:allowBackup="true"

android:icon="@drawable/ic_launcher"

android:label="@string/app_name"

android:theme="@style/AppTheme" >

<activity

android:name="com.example.ndkcallback.MainActivity"

android:label="@string/app_name" >

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

</manifest>