這個例子主要是演示了JNI在實際開發中的開發流程。在實際開發中,android工程師只需要從C/C++工程師那里

拿到底層的一些邏輯代碼,整合到jni目錄下的.c文件即可

代碼的鏈接地址：http://download.csdn.net/detail/caihongshijie6/6651355

一、原理圖

二、效果圖

三、代碼實現

1、MyView

[java]?view plaincopyprint?

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控件的顯示其實都是通過onDraw()?

?????*?canvas?代表的是屏幕的畫布...?

?????*/??

????@Override??

????protected?void?onDraw(Canvas?canvas)?{??

??????????

????????//bottom值?需要根據鍋爐的壓力?動態確定??

????????canvas.drawRect(20,?20,30,bottom,paint);??

????????super.onDraw(canvas);??

????}??

??

??????

}??

2、MainActivity

[java]?view plaincopyprint?

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(){//消息機制的模板代碼。。。在主線程中更新界面??

????????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("鍋爐快爆炸了...快跑吧~~~~~");??

??????????????????

??????????????????

????????????????setContentView(tv);??

????????????????timer.cancel();??

??????????????????

????????????????return?;??

????????????}??

??????????????

??????????????

????????????MyView?myView?=?new?MyView(MainActivity.this,?pressure,?color);??

????????????setContentView(myView);//****這里需要注意,這時不再是通過.xml文件來畫界面??

????????????super.handleMessage(msg);??

????????};??

????};??

??????

??????

????static{??

????????System.loadLibrary("Hello");??

????}??

??????

??????

????@Override??

????protected?void?onCreate(Bundle?savedInstanceState)?{??

????????super.onCreate(savedInstanceState);??

????????//獲取鍋爐壓力?,根據壓力顯示不同的內容??

????????timer?=?new?Timer();??

????????task?=?new?TimerTask()?{??

??????????????

????????????@Override??

????????????public?void?run()?{??

????????????????int?pressure?=?getPressure()%300;??

????????????????System.out.println("壓力:?"?+?pressure);??

??????????????????

????????????????//把壓力顯示到UI界面上??

????????????????Message?msg?=?new?Message();??

????????????????msg.obj?=?pressure;??

????????????????handler.sendMessage(msg);??

????????????}??

????????};??

??????????

????????timer.schedule(task,?1000,2000);??

????}??

??

????/**??

?????*?根據鍋爐壓力,獲取應該顯示的顏色??

?????*?@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;??

????????}??

????}??

????@Override??

????public?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

[cpp]?view plaincopyprint?

#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這個目錄??

#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()的代碼由C/C++工程師提供?

?*/??

int?getpressure(){??

??//?c語言中的隨機數??

????return?rand();??

}??

??

JNIEXPORT?jint?JNICALL?Java_com_njupt_monitor_MainActivity_getPressure??

??(JNIEnv?*?env,?jobject?obj){??

????return?getpressure();??

}??

4、Android.mk

[cpp]?view plaincopyprint?

LOCAL_PATH?:=?$(call?my-dir)??

??

??include?$(CLEAR_VARS)??

??

??LOCAL_MODULE????:=?Hello?????

??LOCAL_SRC_FILES?:=?Hello.c??

??LOCAL_LDLIBS?+=?-llog??

????

??include?$(BUILD_SHARED_LIBRARY)??

5、在此過程中需要用到的命令請參考上一篇博客。。。。

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