Tài liệu Java Threads

Java Threads

@2010 Mihail L Sichitiu 1

Android Introduction

Hello Threads

 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)

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( )

Message

Handler

@2010 Mihail L Sichitiu 5

Main Activity (HelloThreads)

 ClassMembers

TextView isRunning,myIPAddressField,lastMessage;

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 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

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" />