Android Introduction
Hello Threads
@2010 Mihail L. Sichitiu
1
Goal
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Create a basic chat
application that uses
broadcast UDP to send and
receive messages on the
local network (75%)
Improve the chat application
(25%)
You: Your text
@2010 Mihail L. Sichitiu
2
Layout
ListView showing
both the messages sent as
well as received
EditText allowing users
to enter text to be sent
Send button –
sends the text
You: Your text
@2010 Mihail L. Sichitiu
3
Application Structure
ServerThread
Main Activity
Constructor
OnCreate( )
Open the Socket
If successful – “Server Started”
Find the broadcast IP Address
Find the IP Address
Create the thread
Start the thread
run( )
Message
Handler
while (socketStillOpen){
receive packet
display Message
send reply
}
OnDestroy( )
close the socket
sendPacket( )
OnClickListener( )
send UDP
Send Message
@2010 Mihail L. Sichitiu
4
Main Activity (HelloThreads)
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ClassMembers
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OnCreate( )
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EditText
msg;
// For typing the message
Button
send;
// For sending the message
ListView
msgList; // For displaying the message list
ArrayAdapter <String>receivedMessages; // Holds the list of messages
ServerThread
myThread; // The server thread handling all networking
Handler
myHandler...... Similar to the one in HelloThreads
case PACKET_CAME:
String incomingMessage = (String) msg.obj;
receivedMessages.add("You: "+incomingMessage);
Get handles (findViewById) to all GUI elements
msgList = (ListView)findViewById(R.id.msgList);
receivedMessages = new ArrayAdapter<String>(this, R.layout.message);
msgList.setAdapter(receivedMessages);
Create ServerThread: myThread=new
ServerThread(getApplicationContext(),mHandler)
Start the Thread: myThread.start();
Register the OnClickListener for the Send Button
OnDestroy( )
OnClickListener( )
@2010 Mihail L. Sichitiu
5
ServerThread
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public class ServerThread extends Thread
Class Members
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public ServerThread(Context currentContext,Handler handler){
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Handler
mHandler;
// Handler for messages in the main thread
Context
mContext;
// Context to the application (for getting ip Addresses)
DatagramSocket
serverSocket; // Socket used both for sending and receiving
boolean
socketOK=true; // True as long as we don't get socket errors
InetAddress myBcastIPAddress;
// my broadcast IP addresses
InetAddress myIPAddress;
// my IP addresses
mContext = currentContext;
mHandler = handler;
try
 serverSocket = new DatagramSocket(PORT);
 serverSocket.setBroadcast(true); ... catch and handle the exception
try getMyWiFiBcastAndIPAddress(); ... catch and handle the exception
run( ) – similar to HelloThreads, without the reply
sendPacket(String msg) – similar to UDP sender in HelloSockets
@2010 Mihail L. Sichitiu
6
Getting the IP Address:
getMyWiFiBcastAndIPAddress( );
WifiManager mWifi = (WifiManager)
(mContext.getSystemService(Context.WIFI_SERVICE));
WifiInfo info = mWifi.getConnectionInfo();
DhcpInfo dhcp = mWifi.getDhcpInfo();
int myIntegerIPAddress = dhcp.ipAddress;
int myIntBroadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
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
7
Improvements
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Your choice of examples – below are only examples
Different improvements are worth different amount of points
Max points 125%
Examples (only examples – go wild!):
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Add names to the messages
Add images
Add voice
Add preferences
Handle Application lifecycle (on restart, on pause, on resume, etc.)
Vibrate or notify on receipt of a new message
Handle landscape/portrait
Localize it
Looks (background, icon, button, etc.)
Make utility for saving all messages in a file
@2010 Mihail L. Sichitiu
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