JNI开发之锅炉压力监控器

这个例子主要是演示了JNI在实际开发中的开发流程。在实际开发中,android工程师只需要从C/C++工程师那里

拿到底层的一些逻辑代码,整合到jni目录下的.c文件即可

代码的链接地址：http://download.csdn.net/detail/caihongshijie6/6651355

一、原理图

二、效果图

三、代码实现

1、MyView

package com.njupt.monitor;import android.content.Context;import android.graphics.Canvas;import android.graphics.Paint;import android.view.View;public class MyView extends View {private int bottom;private Paint paint;public MyView(Context context,int bottom,int color) {super(context);this.bottom = bottom;paint = new Paint();paint.setColor(color);paint.setStrokeWidth(10);}/** * android下所有的view控件的显示其实都是通过onDraw() * canvas 代表的是屏幕的画布... */@Overrideprotected void onDraw(Canvas canvas) {//bottom值 需要根据锅炉的压力 动态确定canvas.drawRect(20, 20,30,bottom,paint);super.onDraw(canvas);}}

2、MainActivity

package com.njupt.monitor;import java.util.Timer;import java.util.TimerTask;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.app.Activity;import android.graphics.Color;import android.view.Menu;import android.widget.TextView;public class MainActivity extends Activity {public native int getPressure();private Timer timer;private TimerTask task;private Handler handler = new Handler(){//消息机制的模板代码。。。在主线程中更新界面public void handleMessage(android.os.Message msg) {int pressure = (Integer) msg.obj;int color = getColor(pressure);if(color == 404){TextView tv = new TextView(MainActivity.this);tv.setTextColor(Color.RED);tv.setTextSize(30);tv.setText("锅炉快爆炸了...快跑吧~~~~~");setContentView(tv);timer.cancel();return ;}MyView myView = new MyView(MainActivity.this, pressure, color);setContentView(myView);//****这里需要注意,这时不再是通过.xml文件来画界面super.handleMessage(msg);};};static{System.loadLibrary("Hello");}@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);//获取锅炉压力 ,根据压力显示不同的内容timer = new Timer();task = new TimerTask() {@Overridepublic void run() {int pressure = getPressure()%300;System.out.println("压力: " + pressure);//把压力显示到UI界面上Message msg = new Message();msg.obj = pressure;handler.sendMessage(msg);}};timer.schedule(task, 1000,2000);}/** * 根据锅炉压力,获取应该显示的颜色 * @param pressure * @return */public int getColor(int pressure){if(pressure < 100){return Color.GREEN;}else if(pressure < 200){return Color.YELLOW;}else if(pressure < 260){return Color.RED;}else{return 404;}}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}

3、Hello.c

#include <stdio.h>#include <jni.h>#include <stdlib.h>#include "com_njupt_monitor_MainActivity.h"#include <android/log.h>//include  D:\android-ndk-r7b\platforms\android-8\arch-arm\usr\include\android下的log.h这个目录#define LOG_TAG "System.out"#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)/** * getpressure()的代码由C/C++工程师提供 */int getpressure(){  // c语言中的随机数    return rand();}JNIEXPORT jint JNICALL Java_com_njupt_monitor_MainActivity_getPressure  (JNIEnv * env, jobject obj){return getpressure();}

4、Android.mk

 LOCAL_PATH := $(call my-dir)   include $(CLEAR_VARS)   LOCAL_MODULE    := Hello      LOCAL_SRC_FILES := Hello.c   LOCAL_LDLIBS += -llog      include $(BUILD_SHARED_LIBRARY)

5、在此过程中需要用到的命令请参考上一篇博客。。。。