Android Introduction

1
Android Introduction

• Hello Threads

2
Goal

• Create a basic chat application that uses
  broadcast UDP to send and receive messages on the
  local network (75)
• Improve the chat application (25)

3
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
4
Application Structure
ServerThread
Main Activity
Constructor Open the Socket If successful
Server Started Find the broadcast IP
Address Find the IP Address
OnCreate( ) Create the thread Start the
thread
run( ) while (socketStillOpen) receive
packet display Message send reply
Message Handler
OnDestroy( ) close the socket
sendPacket( ) send UDP
OnClickListener( ) Send Message
5
Main Activity (HelloThreads)

• ClassMembers
• EditText msg // For typing the message
• Button send // For sending the
  message
• ListView msgList // For displaying the
  message list
• ArrayAdapter ltStringgtreceivedMessages // Holds
  the list of messages
• ServerThread myThread // The server thread
  handling all networking
• Handler myHandler...... Similar to the one in
  HelloThreads
• OnCreate( )
• Get handles (findViewById) to all GUI elements
• msgList (ListView)findViewById(R.id.msgList)
• receivedMessages new ArrayAdapterltStringgt(this,
  R.layout.message)
• msgList.setAdapter(receivedMessages)
• Create ServerThread myThreadnew
  ServerThread(getApplicationContext(),mHandler
  )
• Start the Thread myThread.start()
• Register the OnClickListener for the Send Button
• OnDestroy( )
• OnClickListener( )

case PACKET_CAME String incomingMessage
(String) msg.obj receivedMessages.add("You
"incomingMessage)
6
ServerThread

• public class ServerThread extends Thread
• Class Members
• 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 socketOKtrue // True as long as we
  don't get socket errors
• InetAddress myBcastIPAddress // my broadcast
  IP addresses
• InetAddress myIPAddress // my IP addresses
• public ServerThread(Context currentContext,Handler
  handler)
• 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

7
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 byte4
• for (int k 0 k lt 4 k)
• quadsk (byte) ((myIntegerIPAddressgtgt k
  8) 0xFF)
• try
• InetAddress myIPAddress InetAddress.getByAdd
  ress(quads)
• return myIPAddress
• catch(Exception e)
• if(D) Log.e(TAG,"Cannot Get My Own IP
  Address")
• return null

8
Improvements

• Your choice of examples below are only examples
• Different improvements are worth different amount
  of points
• Max points 125
• Examples (only examples go wild!)
• 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