[導(dǎo)讀]前幾天學習了 Android 下 Socket 編程。學習 Socket 編程是有目的的，需要完成在手機與 PC 之間的通訊。通訊的內(nèi)容是將手機上播放的 MP3 信息，通過 Socket 傳輸?shù)?PC
前幾天學習了 Android 下 Socket 編程。
學習 Socket 編程是有目的的，需要完成在手機與 PC 之間的通訊。通訊的內(nèi)容是將手機上播放的 MP3 信息，通過 Socket 傳輸?shù)?PC 端。
在參考網(wǎng)上相關(guān) Socket 的文章后，基本上完成了 Socket 功能。所以就繼續(xù)學習 Android 下音樂播放器的實現(xiàn)。在實現(xiàn)音樂播放器過程中，發(fā)現(xiàn)由于音樂播放器至少要有播放列表和正在播放兩個 Activity，這樣問題就來了：
(1). Socket 只是在第一個 Activity 中實現(xiàn)了，當這個 Activity 活動時沒有問題。但此 Activity 非活動時，不能處理 Socket。
(2). 當反復(fù)進入第一個 Activity 時，會出現(xiàn) Socket 初始化報錯的問題。出現(xiàn)這樣的錯誤，是由于 Sokcet 的初始化放在第一個 Activity 的 onCreate 中。
由于在做音樂播放器時使用了 Service，所以想到用 Serivce 來處理 Socket 應(yīng)該沒有問題。但是否有其它的方法呢？由于個人是剛剛接觸 Android 編程，就不能確定這個問題了！
在論壇提問，得到的答案是:(1) Serivce; (2) 也可以更改activity的啟動方式，讓串口不重復(fù)創(chuàng)建。顯然，第二種方法還沒有接觸過。采用第一種 Serivce 來實現(xiàn)更可靠一些。
首先，實現(xiàn) Socket Service。
package?com.jia.leozhengfirstapp;
import?java.io.IOException;
import?java.io.InputStream;
import?java.io.UnsupportedEncodingException;
import?java.net.ServerSocket;
import?java.net.Socket;
import?android.app.Service;
import?android.content.BroadcastReceiver;
import?android.content.Context;
import?android.content.Intent;
import?android.content.IntentFilter;
import?android.os.IBinder;
import?android.util.Log;
public?class?SocketService?extends?Service?{
??private?Socket?clientSocket?=?null;
??private?ServerSocket?mServerSocket?=?null;
??private?SocketAcceptThread?socketAcceptThread?=?null;
??private?SocketReceiveThread?socketReceiveThread?=?null;
??private?SocketReceiver?socketReceiver;
??public?static?final?String?SOCKER_ACTION?=?"com.jia.Socket.Control";
??public?static?final?String?SOCKER_RCV?=?"com.jia.Socket.ReceiveStr";
??private?boolean?stop?=?true;
??@Override
??public?IBinder?onBind(Intent?intent)?{
????//?TODO?Auto-generated?method?stub
????return?null;
??}
???@Override
??public?void?onCreate()?{
??????????super.onCreate();
??????????Log.d("service",?"socket?service?created");
??????????socketReceiver?=?new?SocketReceiver();
??????????IntentFilter?filter?=?new?IntentFilter();
??????????filter.addAction(SOCKER_ACTION);
??????????registerReceiver(socketReceiver,?filter);
??????????socketAcceptThread?=?new?SocketAcceptThread();
????????????//?開啟?Socket?監(jiān)聽線程
????????????socketAcceptThread.start();
???}
??@Override
??public?void?onStart(Intent?intent,?int?startId)?{
?????Log.d("service",?"socket?service?start");
??}
??@Override
??public?void?onDestroy()?{
??Log.d("service",?"socket?service?destroy!");
??}
??public?class?SocketReceiver?extends?BroadcastReceiver?{
????@Override
????public?void?onReceive(Context?context,?Intent?intent)?{
??????String?action?=?intent.getAction();
????????????if(action.equals(SOCKER_ACTION))?{
??????????????String?sub_action?=?intent.getExtras().getString("ACTION");
??????????????if(sub_action.equals("reconnect"))?{
????????????????Log.d("service",?"socket?service:?reconnect.");
?????????????????socketAcceptThread?=?new?SocketAcceptThread();
??????????????????//?開啟?Socket?監(jiān)聽線程
??????????????????socketAcceptThread.start();
??????????????}
????????????}
????}
??}
??private?class?SocketAcceptThread?extends?Thread
??{
???????@Override
???????public?void?run()
???????{
?????????Log.d("service",?"socket?service?-?SocketAcceptThread::run");
???????????try?{
???????????????//?實例化ServerSocket對象并設(shè)置端口號為?12589
???????????????mServerSocket?=?new?ServerSocket(12589);
???????????}?catch?(IOException?e)?{
???????????????//?TODO?Auto-generated?catch?block
???????????????e.printStackTrace();
???????????}
???????????try?{
???????????????//?等待客戶端的連接（阻塞）
???????????????clientSocket?=?mServerSocket.accept();
???????????}?catch?(IOException?e)?{
???????????????//?TODO?Auto-generated?catch?block
???????????????e.printStackTrace();
???????????}
???????????socketReceiveThread?=?new?SocketReceiveThread(clientSocket);
???????????stop?=?false;
???????????//?開啟接收線程
???????????socketReceiveThread.start();
?????????????Intent?sendIntent?=?new?Intent(SOCKER_RCV);
?????????????sendIntent.putExtra("action",?"ClientIP");
?????????????sendIntent.putExtra("content",?clientSocket.getInetAddress().getHostAddress());
?????????????//?發(fā)送廣播，將被Activity組件中的BroadcastReceiver接收到
?????????????sendBroadcast(sendIntent);
???????}
???}
???private?class?SocketReceiveThread?extends?Thread
???{
???????private?InputStream?mInputStream?=?null;
???????private?byte[]?buf;
???????private?String?str?=?null;
???????Socket?sUsed;
???????SocketReceiveThread(Socket?s)
???????{
?????????Log.d("service",?"socket?service?-?SocketReceiveThread");
???????????try?{
???????????????//?獲得輸入流
???????????????this.mInputStream?=?s.getInputStream();
???????????????sUsed?=?s;
???????????}?catch?(IOException?e)?{
???????????????//?TODO?Auto-generated?catch?block
???????????????e.printStackTrace();
???????????}
???????}
???????@Override
???????public?void?run()
???????{
?????????Log.d("service",?"socket?service?-?SocketReceiveThread::run");
???????????while((!stop)?&&?(!mServerSocket.isClosed()))
???????????{
???????????????this.buf?=?new?byte[2048];
???????????????//?讀取輸入的數(shù)據(jù)(阻塞讀)
???????????????try?{
???????????????????this.mInputStream.read(buf);
???????????????}?catch?(IOException?e1)?{
???????????????????//?TODO?Auto-generated?catch?block
???????????????????e1.printStackTrace();
???????????????}
???????????????//?字符編碼轉(zhuǎn)換
???????????????try?{
???????????????????this.str?=?new?String(this.buf,?"GB2312").trim();
???????????????}?catch?(UnsupportedEncodingException?e)?{
???????????????????//?TODO?Auto-generated?catch?block
???????????????????e.printStackTrace();
???????????????}
???????????????Intent?sendIntent?=?new?Intent(SOCKER_RCV);
???????????????sendIntent.putExtra("action",?"RcvStr");
???????????????sendIntent.putExtra("content",?this.str);
???????????????//?發(fā)送廣播，將被Activity組件中的BroadcastReceiver接收到
???????????????sendBroadcast(sendIntent);
???????????}
???????}
???}
}
在每個 Activity 中處理 SOCKER_RCV action，以響應(yīng) Socket 狀態(tài)的變化和接收到數(shù)據(jù)。
Service 與 Activity 之間通訊需要使用到廣播: Broadcast。
(1) 在 Activity 中定義全局的變量，如下：
public?static?final?String?SOCKER_ACTION?=?"com.jia.Socket.Control"; public?static?final?String?SOCKER_RCV?=?"com.jia.Socket.ReceiveStr"; SocketReceiver?socketReceiver;
(2) 在 Activity 的 onCreate 中注冊廣播和啟動 Socket Service，如下：
socketReceiver?=?new?SocketReceiver(); IntentFilter?socketIntentFilter?=?new?IntentFilter(); socketIntentFilter.addAction(SOCKER_RCV); registerReceiver(socketReceiver,socketIntentFilter); Intent?socketIntent?=?new?Intent(); socketIntent.setClass(MainActivity.this,?SocketService.class); startService(socketIntent);???????//?啟動??Socket?服務(wù)
(3) SocketReceiver 是繼承自 BroadcastReceiver 的類，實現(xiàn)如下：
public?class?SocketReceiver?extends?BroadcastReceiver?{
??@Override
??public?void?onReceive(Context?context,?Intent?intent)?{
????//?TODO?Auto-generated?method?stub
????String?action?=?intent.getAction();
??????????if(action.equals(SOCKER_RCV))?{
????????????String?url?=?intent.getExtras().getString("action");
????????????if(url.equals("ClientIP"))?{
??????????????String?strIP?=?intent.getExtras().getString("content");
????????????}
????????????else?if(url.equals("RcvStr"))?{
??????????????String?strContent?=?intent.getExtras().getString("content");
????????????}
????????????else?if(url.equals("Disconnect"))?{
??????????????String?strContent?=?intent.getExtras().getString("content");
????????????}
????????}
????}
}
(4) Socket 功能實現(xiàn)后，測試時發(fā)現(xiàn)客戶端(也就是 PC 端)斷開時手機端未檢測到 Socket 連接斷開。
以前使用 WinCE 時，Socket(TCP) 斷開時，無論是客戶端、還是服務(wù)器都可以檢測到 TCP 斷開的事件，并處理。但 Android 下的 Socket 編程機制竟然沒有這個東東。
一，測試時發(fā)現(xiàn)當 PC 端斷開后，手機端的服務(wù)程序在執(zhí)行到下面的代碼段時不會阻塞，且函數(shù)的返回值是: -1。
二，在網(wǎng)上查找發(fā)現(xiàn)這個問題是 Android 下 Socket 都有的問題，可以通過發(fā)心跳包來處理。
所以將下面這段代碼:
//?讀取輸入的數(shù)據(jù)(阻塞讀)
try?{
????this.mInputStream.read(buf);
}?catch?(IOException?e1)?{
????//?TODO?Auto-generated?catch?block
????e1.printStackTrace();
}
修改為如下的代碼:?
try?{
????int?length?=?this.mInputStream.read(buf);
????if(-1?==?length)?{
??????try?{
????????sUsed.sendUrgentData(0xff);
??????}
??????catch(Exception?ex)?{
????????//?鏈接已斷開
????????Log.v("service",?"disconnect!!!");
????????stop?=?true;
????????if(null?!=?mServerSocket)?{
??????????mServerSocket.close();
????????}
????????Intent?sendIntent?=?new?Intent(SOCKER_RCV);
????????sendIntent.putExtra("action",?"Disconnect");
????????sendIntent.putExtra("content",?"read?is?-1?&?Urgent?Exception!");
????????sendBroadcast(sendIntent);
????????continue;
??????}
????}
}?catch?(IOException?e1)?{
????//?TODO?Auto-generated?catch?block
????e1.printStackTrace();
} 
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