安卓页面切换时与服务器的连接就断开了

与服务器的连接方式是用socket
有人提议用后台服务，但试过了没有成功，求助哪里错误。
service代码：
public class MyService extends Service {
    private static final String TAG = "TestService";
    public static Socket socket= null;//声明套接字类

    public IBinder onBind(Intent i) {
        Log.e(TAG, "============> MyService.onBind");
        return null;
    }

    //service创建时调用
    public void onCreate() {
        super.onCreate();
        new Thread(){
         @Override
public void run(){
//连接到服务器
try {
socket= new Socket("10.200.181.237",1230);
}
catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();//打印异常
}
finally{
try{
if(socket != null){
socket.close();
socket= null;
    }
}
catch(Exception e){
e.printStackTrace();
}
}
}
   }.start();
    }

    public void onStart(Intent intent,int startId){
        Log.e(TAG, "============> MyService.onStart");
        super.onStart(intent, startId);
    }

    public void onDestroy() {
        Log.e(TAG, "============> TestService.onDestroy");
        super.onDestroy();
    }


}

页面代码：
public class MainActivity extends Activity{
public static EditText username =null;//声明用户名编辑框，用于用户输入用户名
private EditText password =null;//声明密码编辑框，用于用户输入密码
CheckBox cb = null;//记住密码
private String string="";

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button loginbutton=(Button)findViewById(R.id.button1);
cb = (CheckBox)findViewById(R.id.checkBox1);
username=(EditText)findViewById(R.id.editText1);
password=(EditText)findViewById(R.id.editText2);
loginbutton.setOnClickListener(startListener);
}
private OnClickListener startListener=new OnClickListener()
{
@Override
public void onClick(View v)
{
Intent intent = new Intent();
intent.setAction(".Myservice");
startService(intent);
String editUid = username.getText().toString();
String editPwd = password.getText().toString();
DataOutputStream dout = null;
DataInputStream din = null;
//连接到服务器
try {

dout = new DataOutputStream(MyService.socket.getOutputStream());//向服务器发送消息
din = new DataInputStream(MyService.socket.getInputStream()); //接收服务器消息
dout.writeUTF("Login,"+username.getText().toString()+","+password.getText().toString());
String msg = din.readUTF();//msg用于保存来自服务器的消息

Intent intent1 = new Intent();
intent1.setClass(MainActivity.this, Login_Ok.class);
}
catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();//打印异常
}
finally{
try{
if(din != null){
din.close();
din = null;
}
}
catch(Exception e){
e.printStackTrace();
}
try{
if(dout != null){
dout.close();
dout = null;
}
}
catch(Exception e){
e.printStackTrace();
}
}

}

};

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}

Android 服务器 service 求助

补充：移动开发 ,  Android