如何访问线程内的类级变量，我试图直接访问变量但发生异常。是否可以访问线程内的类级变量，或者我必须使用handler？
这是我的代码。
public class MainMapActivity extends MapActivity
{
//***************************************************************************************
//isRouteDisplayed Method (Override)
@Override
protected boolean isRouteDisplayed()
{
return false;
}//End method
//***************************************************************************************
//private Handler handlerTimer = new Handler();
//***************************************************************************************
//Class Level Variables & Objects
String[] Device_ID = null;
//***************************************************************************************
//onCreate method (Override the built-in method) Called when the activity is first created.
@Override
public void onCreate(Bundle savedInstanceState)
{
//handlerTimer.removeCallbacks(taskUpdateStuffOnDialog);
//handlerTimer.postDelayed(taskUpdateStuffOnDialog , 100);
//service = new NewService();
new Thread(taskUpdateStuffOnDialog).start();
// GIve the Server some time for startup
try
{
Thread.sleep(500);
}
catch (InterruptedException e)
{
}
// Kickoff the Client
// startService(new Intent(this, NewService.class));
new Thread(new NewService()).start();
}//End onCreate
//***************************************************************************************
private Runnable taskUpdateStuffOnDialog = new Runnable()
{
public void run()
{
GlobalVariable appState = ((GlobalVariable)getApplicationContext());
try
{
serverAddr = InetAddress.getByName(SERVERIP);
Log.d("UDP", "S: Connecting...");
/* Create new UDP-Socket */
socket = new DatagramSocket(SERVERPORT, serverAddr);
}
catch (Exception e)
{
Log.e("UDP", "S: Error", e);
}
while(true)
{
// TODO Auto-generated method stub
try
{
/* Retrieve the ServerName */
/* By magic we know, how much data will be waiting for us */
byte[] buf = new byte[72];
/* Prepare a UDP-Packet that can
* contain the data we want to receive */
DatagramPacket packet = new DatagramPacket(buf, buf.length);
Log.d("UDP", "S: Receiving...");
/* Receive the UDP-Packet */
socket.receive(packet);
String id = new String(packet.getData());
//buffer.order(ByteOrder.LITTLE_ENDIAN); // if you want little-endian
String[] tokens = id.split(" ");
String b = tokens[0];
Log.d("Message: ", b + " " );
/***************************** sending device ID *************************************/
else if(b.equals("5"))
{
Device_ID[0] = tokens[1];
runOnUiThread(new Runnable()
{
public void run()
{
String id = tokens[1];
Log.d("UDP", "S: Received Device ID: '" + id + "'");
setID(id);
//positionOverlay.setID(id);
//addEvent(id);
Toast.makeText(MainMapActivity.this, "Your Device ID " + id,Toast.LENGTH_LONG).show();
}
});
//Toast.makeText(MainMapActivity.this, "Your Device ID " + b,Toast.LENGTH_LONG).show();
} // end else if
} // end try
catch (Exception e)
{
Log.e("UDP", "S: Error", e);
} // end catch
//handlerTimer.postDelayed(this, 100);
} // end while condition
//***************************************************************************************
}//End Run method
//***************************************************************************************
};//End Thread
//***************************************************************************************
}
异常是此行Device_ID[0] = tokens[1];
处的空指针异常。
答案 0 :(得分：2)
对我来说，这看起来不像语法上有效的Java。您应该看到编译错误，告诉您ClassToken = token;未被识别。如果它已经过了那个，那么另一个人说你没有宣布run()方法。并且缺少分号。
如果您想发布提供错误的真实代码，我们可能会告诉您真正的问题是什么。
问题是您已将Device_ID初始化为null而不是数组。当您尝试索引null时，您将获得一个NPE。
简单的解决方法是将初始化更改为：
String[] Device_ID = new String[1];
（从您给出的代码中，我看不出为什么你需要使用数组。为什么不让Device_ID成为String？OTOH，也许这只是一个人工制品你的演示代码......）
答案 1 :(得分：-1)
似乎你从来没有将数组deviceId []初始化为除null之外的任何东西 - 所以你明显得到空指针异常