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Java Threads
@2010 Mihail L. Sichitiu 1 Android Introduction Hello Threads @2010 Mihail L. Sichitiu 2 Goal Create an application that uses a background thread as a UDP server to receive messages from the UDP client 152.4.244.125 Text sent from UDPClient @2010 Mihail L. Sichitiu 3 Layout 152.4.244.125 Text sent from UDPClient TextView that changes from “Starting Server” to “Server Started” (optional) TextView that shows the text sent from UDPClient TextView that shows the IP address of the server (needed for UDPClient) Clear Button – clears the Last Message (and shows that interface is still responsive) @2010 Mihail L. Sichitiu 4 Application Structure Main Activity ServerThread UDPClient OnCreate( ) Create the thread Start the thread OnDestroy( ) close the socket Constructor Open the Socket If successful – “Server Started” Find and display the IP Address run( ) while (socketStillOpen){ receive packet display Message send reply } Read line from input Send line to Server Receive line from Server Display line OnClickListener( ) Clear the Last Message Message Handler HelloThreads UDPClient @2010 Mihail L. Sichitiu 5 Main Activity (HelloThreads) ClassMembers TextView isRunning,myIPAddressField,lastMessage; Button clear; ServerThread myThread; Handler OnCreate( ) Get handles (findViewById) to all GUI elements Create ServerThread: myThread=new ServerThread(getApplicationContext(),mHandler) Start the Thread: myThread.start(); Register the OnClickListener for the Clear Button OnDestroy( ) myThread.closeSocket(); OnClickListener( ) Clear the Last Message Handler Definition on Next page The Handler Definition private final Handler mHandler = new Handler() { public void handleMessage(Message msg) { switch (msg.what) { case PACKET_CAME: String incomingMessage = (String) msg.obj; lastMessage.setText(incomingMessage); break; case IS_RUNNING: String socketStatus = (String) msg.obj; isRunning.setText(socketStatus); break; case IP_ADDRESS: InetAddress myIPAddress = (InetAddress) msg.obj; myIPAddressField.setText("Server IP Address:"+myIPAddress.toString()); break; } } }; @2010 Mihail L. Sichitiu 6 @2010 Mihail L. Sichitiu 7 ServerThread public class ServerThread extends Thread Class Members Handler mHandler; // link to the Message Handler Context mContext; // link to application context DatagramSocket serverSocket; // the UDP socket we’ll receive at public ServerThread(Context currentContext,Handler handler){ mContext = currentContext; mHandler = handler; Open the socket; if successful mHandler.obtainMessage(HelloThreads2.IS_RUNNING, "Server Started").sendToTarget(); InetAddress myIP = getMyWiFiIPAddress(); mHandler.obtainMessage(HelloThreads2.IP_ADDRESS, myIP).sendToTarget(); public void closeSocket() serverSocket.close(); public void run() Allows the socket to be closed (call from OnDestroy()) On Next Page On Next Next Page @2010 Mihail L. Sichitiu 8 Getting the IP Address: getMyWiFiIPAddress( ); WifiManager mWifi = (WifiManager) (mContext.getSystemService(Context.WIFI_SERVICE)); WifiInfo info = mWifi.getConnectionInfo(); DhcpInfo dhcp = mWifi.getDhcpInfo(); int myIntegerIPAddress = dhcp.ipAddress; byte[] quads = new byte[4]; for (int k = 0; k < 4; k++) quads[k] = (byte) ((myIntegerIPAddress>> k * 8) & 0xFF); try{ InetAddress myIPAddress = InetAddress.getByAddress(quads); return myIPAddress; }catch(Exception e){ if(D) Log.e(TAG,"Cannot Get My Own IP Address"); return null } @2010 Mihail L. Sichitiu 9 ServerThread.run( ) boolean socketOK=true; // True as long as we don't get socket errors while(socketOK) { DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); try{ serverSocket.receive(receivePacket); /*** . Same as the UDP server ****/ mHandler.obtainMessage(HelloThreads2.PACKET_CAME,sentence). sendToTarget(); } catch (Exception e){ socketOK = false; }// try }// while(socketOK) To the Message Handler in the main Thread Blocks Handles multiple requests as long as the socket is OK Android Manifest To be able to use the Internet (open sockets) and to read our own IP address (from the WiFi Manager): <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> @2010 Mihail L. Sichitiu 10 . Clear the Last Message Message Handler HelloThreads UDPClient @2010 Mihail L. Sichitiu 5 Main Activity (HelloThreads) ClassMembers TextView isRunning,myIPAddressField,lastMessage;. mHandler.obtainMessage(HelloThreads2.IS_RUNNING, "Server Started").sendToTarget(); InetAddress myIP = getMyWiFiIPAddress(); mHandler.obtainMessage(HelloThreads2.IP_ADDRESS,