Windows Phone 8 - 13 Near Field Communcations and Bluetooth

Oliver Scheer

Senior Technical Evangelist

Microsoft Deutschland

http://the-oliver.com

Near Field Communications and Bluetooth

This App This App

04/12/2023Microsoft confidential2

Agenda

Local Communication with Windows Phone

Bluetooth Overview

Using Bluetooth from an application

Near Field Communications (NFC)

Using NFC from an application

Local Communication

How to create applications and games that pass

information directly between two devices which are in

close proximity


• Local Communication is new to Windows Phone 8

• In Windows Phone 7 processes had to communicate using network connections• This was difficult because programs had to determine the required IP

address

• In Windows Phone 8 there are two new local communication methods available

• Bluetooth• Can be used for phone to phone and phone to device communication over

a range of up to 10 meters

•Near Field Communication (NFC)• Can be used for phone to device communication in very close proximity

Local Communication with Windows Phone 8


Bluetooth


• Bluetooth is a short range wireless communication technology •Nominally the range is up to 10 metres, but this can be reduced by the

conditions

• Bluetooth provides a means by which one device can provide services for

another• A Bluetooth connection is always between two parties

• A device which has made itself “discoverable” can publish a list of services it

provides

•Other devices can search for discoverable devices and then request a the list

of resources that the device provides

• The Bluetooth connection is provided to the program in the form of a

StreamSocket instance linked to the remote device

Bluetooth Communications


• For one device to be able to communicate with the other the two may need to

be paired

• A device must be made “discoverable” before pairing can take place• Pairing is normally performed via the settings screen on the device

•During the pairing the connection is authenticated

• The user may need to enter a key to validate the connection• This may be a fixed key, as in the case of devices such as headsets, or

generated by one device and entered on the other

• In some situations applications can communicate without needing to be paired

Bluetooth Pairing


• There are two Bluetooth communication scenarios supported by Windows

Phone

• App to device• A program running on a Windows Phone can establish a connection to an

external device • The Windows Phone must be paired with the device

• App to app• A program running on a Windows Phone can find another application that

is offering a service that the device wishes to use• In this situation pairing is not required

Bluetooth Scenarios


• An application running on a Windows Phone 8 device can obtain an

enumeration of all the Bluetooth devices that have been paired with the phone

• The application can then attempt to make a connection to the required service

on that device

• For this to work the Bluetooth service on the phone must be turned on

• The ID_CAP_PROXIMITY and ID_CAP_NETWORKING capabilities must be

enabled for the application to make use of the Bluetooth communications to a

device

App to Device

• The PeerFinder class can be used to search for paired devices

• The search will fail with the exception shown above if Bluetooth is switched off

Finding Paired devices

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try{ PeerFinder.AlternateIdentities["Bluetooth:Paired"] = ""; var peers = await PeerFinder.FindAllPeersAsync();}catch (Exception ex){ if ((uint)ex.HResult == 0x8007048F) MessageBox.Show("Bluetooth is switched off");}

• If the user needs to turn Bluetooth on the application can open the appropriate

Settings page using the ConnectionSettingsTask launcher

• Alternatively, use the LaunchUriAsync method:

Enabling Bluetooth

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ConnectionSettingsTask connectionSettingsTask = new ConnectionSettingsTask();connectionSettingsTask.ConnectionSettingsType = ConnectionSettingsType.Bluetooth;connectionSettingsTask.Show();

Windows.System.Launcher.LaunchUriAsync(new Uri("ms-settings-bluetooth"));

• A call of FindAllPeersAsync will return with a list of PeerInformation values,

each of which describes a paired device that was discovered

• This includes a display name for the host, the name of the service it provides

and a HostName value which gives more detail about the device

• If no peers are found the list is empty , with a count of 0

• This task can also be used to provide quick access to other settings

Using the PeerInformation returned from PeerFinder

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StringBuilder list = new StringBuilder();

foreach (PeerInformation p in peers){ list.AppendLine(p.DisplayName);}

• The ConnectAsync method will set up a StreamSocket that connects to a

particular service on the device• The application must search for the service that it wishes to interact with

• The example below just connects to the service provided by the first peer

found

• The method will throw an exception if either parameter is null or empty


Connection to a remote device

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// Just use the first PeerPeerInformation partner = peers[0];

// Attempt a connectionStreamSocket socket = new StreamSocket();

await socket.ConnectAsync(partner.HostName, partner.ServiceName);


• The Bluetooth discovery and connection methods provide the raw ability to

transfer data between the devices• This is the StreamSocket that is created as part of the setup process

• The application will have to implement the communications protocol that is

required for a particular device •Messages in this format will need to be exchanged between the

application and the device

Interacting with Remote Devices via Bluetooth


• App to App communication allows two programs to interact using Bluetooth to

exchange messages

• An application can wait for and respond to messages from another application

• The PeerFinder class exposes an event which is raised when a communication

request is received from another system

• The communication is still performed using a SocketStream that links the two

programs

• The devices do not need to be paired in order to implement app to app

connection

• The ID_CAP_PROXIMITY capability must be enabled for the application

App to App communication

• An application can advertise itself as accepting connections by setting the

display name for the PeerFinder and then starting to advertise the service

•Note that doing this for a long time may have an adverse effect on battery life


Advertising a Service for other Applications

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// Register for incoming connection requestsPeerFinder.ConnectionRequested += PeerFinder_ConnectionRequested;

// Start advertising ourselves so that our peers can find usPeerFinder.DisplayName = "PSR";PeerFinder.Start();

• An application can subscribe to the ConnectionRequested event

•When the event fires the application can then decide whether to accept the

request

• It could display a confirmation dialog to the user


Waiting for an Incoming Connection

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// Register for incoming connection requestsPeerFinder.ConnectionRequested += PeerFinder_ConnectionRequested;

// Start advertising ourselves so that our peers can find usPeerFinder.DisplayName = "PSR";PeerFinder.Start();

• The above method creates a connection to an incoming request from

“RobsPhone”

• It uses the PeerInformation property of the ConnectionRequestedEventArgs

to determine who is attempting to connect


Responding to a Connection Request

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StreamSocket socket;

async void PeerFinder_ConnectionRequested(object sender, ConnectionRequestedEventArgs args){ if ( args.PeerInformation.DisplayName == "RobsPhone" ) { socket = await PeerFinder.ConnectAsync(args.PeerInformation); PeerFinder.Stop(); }}

• This checks the name of the incoming request and only responds to messages

from “RobsPhone”

• The application could instead display a confirmation dialog for the user that

identifies the source of the request



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• This statement creates the socket

• In a complete application there should be a handler for any exceptions that this

action might produce



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• This statement stops the phone from advertising the connection to other

devices

• This will prevent further requests and also improve power consumption



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• This method will read a string of text from the stream socket

• The message is read as a length value, followed by that number of characters

Application to Application Communication

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private DataReader dataReader;

private async Task<string> GetMessage(){ if (dataReader == null) dataReader = new DataReader(socket.InputStream); await dataReader.LoadAsync(4); uint messageLen = (uint)dataReader.ReadInt32(); await dataReader.LoadAsync(messageLen); return dataReader.ReadString(messageLen);}

• This is the DataReader that will be used to extract information from the

StreamSocket


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• This is the DataReader that will be used to extract information from the

StreamSocket

• The DataReader is created the first time the method is called


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• This statement loads 4 bytes from the input stream


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• This statement loads 4 bytes from the input stream

• The incoming 4 bytes are converted into an integer, which is the number of

bytes that are being transferred


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• This statement loads the text of the string

• It uses the value that was supplied as the length


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• This statement loads the text of the string

• It uses the value that was supplied as the length

•Once the bytes have been received they are converted into a string that is

returned by the task


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• This GetMessage method is a Task which can be started using the await

keyword as shown above

• This is using the Win RT task management which is provided as part of the

Windows 8 Libraries

•When the task completes the message will be set to the received string

Initiating the Read

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string message = await GetMessage();

• The SendMessage method is given a string that it sends to output stream

• It uses a DataWriter to format the output

Writing the message

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DataWriter dataWriter;

private async void SendMessage(string message){ if ( dataWriter == null) dataWriter = new DataWriter(socket.OutputStream); dataWriter.WriteInt32(message.Length); await dataWriter.StoreAsync();

dataWriter.WriteString(message); await dataWriter.StoreAsync();}

• The dataWriter is created from the socket if it does not already exist

Writing the message

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• The first item that is written is the length of the string

Writing the message

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• The first item that is written is the length of the string

• This is followed by the string data itself

Writing the message

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• The message transmitter method is not implemented as a task

• It can just be called when the message is to be sent

Writing the message

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• The SendMessage and GetMessage methods implement each end of a simple

protocol that serialises a message between the sender and the receiver

• If you want to send more complex data you can make use of appropriate

serialisation techniques to assemble the message text, just as you would

between any processes which are each end of a data channel

Messages and Protocols


• It is not possible to use the emulator to debug a program that uses Bluetooth

• An application can check to determine if the emulator is being used and

behave appropriately

Creating Bluetooth Solutions

if (Microsoft.Devices.Environment.DeviceType == Microsoft.Devices.DeviceType.Emulator){ MessageBox.Show("No Bluetooth on the emulator");

}


Near Field Communications (NFC)


•Near Field Communications provide a connection between devices that are

very close together (within 3-4 centimetres)

• The data is transferred at a rate of up to 424 Kbits/second

• It is assumed that this data transfer is intentional so there is not normally any

authentication as such• The user has positioned their device close to the other device

• The phone can connect to an unpowered NFC chip/tag

Near Field Communications


•NFC is best for sending small amounts of data between devices and can be

used in a number of different scenarios:

• Connect devices.• pass configuration from one device to another

• Acquire content• read “smart” posters that contain digital content in an embedded NFC tag.

• Exchange digital objects• exchange an electronic business card, or vCard.

Using Near Field Communications


• There are two ways that an application can use NFC

• Simple transfer of a message from one device to another• An application can subscribe to message events and receive a string

message of a particular type

• An NFC connection can be used to configure a connection which is

implemented using Bluetooth or WiFi• This extends the PeerFinder to allow an application to use NFC to quickly

set up a StreamSocket between two devices

Using NFC in applications


• It is very easy to publish a message to NFC•Messages have a messagetype and a payload

• The PublishMessage method returns an ID value that uniquely identifies the

message that was sent

• This can then be used to manage the message

Publishing a Message

ProximityDevice device = ProximityDevice.GetDefault();

// Make sure NFC is supportedif (device!= null){ long id = device.PublishMessage("Windows.SampleMessageType", "Hello From Rob!");}


• The SubscribeForMessage method is given the message type and a delegate

• In the above code the message type is “Windows.SampleMessageType”• You can add your own message types for your particular solution

Subscribing to Messages


// Make sure NFC is supportedif (device!= null){ long id = device.SubscribeForMessage ("Windows.SampleMessageType", messageReceived); }


•When a message is received the event is raised and the program can make use

of the received data

• This event is fired when the received message has the same type • In the case of our program it will fire when a message of type

“Windows.SampleMessageType” is recevied

Receiving Messages

private void messageReceived(ProximityDevice sender, ProximityMessage message){ MessageBox.Show("Message received " + message.DataAsString + " from " + sender.DeviceId);}


• If an application no longer wishes to subscribe to messages it can use the

StopSubscribingForMessage method to request this

• The method is provided with the message id that was returned when the

subscription was first set up

• An application may need to store this value in in case it is made dormant or

tombstoned when using Near Field Communications

Ending a subscription

device.StopSubscribingForMessage(id);


• The PeerFinder class allows an application to bind to an event fired when

another application attempts to set up connection with this device

Setting up a StreamSocket using NFC


// Make sure NFC is supportedif (device != null){ PeerFinder.TriggeredConnectionStateChanged += OnTriggeredConnectionStateChanged; // Start finding peer apps, while making this app discoverable by peers PeerFinder.Start();}


• The event arguments contain a state change message

Setting up a StreamSocket using NFCvoid OnTriggeredConnectionStateChanged(object sender, TriggeredConnectionStateChangedEventArgs args) { switch (args.State) { case TriggeredConnectState.Listening: // Connecting as host break; case TriggeredConnectState.PeerFound: // Proximity gesture is complete – setting up link break; case TriggeredConnectState.Connecting: // Connecting as a client break; case TriggeredConnectState.Completed: // Connection completed, get the socket streamSocket = args.Socket; break; case TriggeredConnectState.Canceled: // ongoing connection canceled break; case TriggeredConnectState.Failed: // Connection was unsuccessful break; }}


• The StreamSocket will be created using WiFi or Bluetooth to transfer the data

• An application can configure the networking technologies by setting these

properties• They are both set to true by default

•Note that for a successful infrastructure network connection both devices must

be connected to the same subnet and be able to directly connect each other

• It is advisable to make sure that Bluetooth is switched on before using this

mechanism, otherwise it might not be possible for the devices to connect in

this way

Using the connection

PeerFinder.AllowBluetooth = true;PeerFinder.AllowInfrastructure = true;


• An application running on a Windows Phone device can be interrupted at any

time• An incoming phone call, text message or the user pressing the Start button

will cause the application to be made dormant and possibly tombstoned

•When an application is made dormant all active network connections are

disconnected as it is no longer able to run in response to incoming messages

•However, Windows 8 provides a reconnection feature that an application can

use to quickly re-establish a connection that was disrupted in this way

• An application can persist connection configuration values that allows the

socket to be recreated when it resumes

Recreating a Connection


• The statements above persist the RawName and RemoteServiceName properties

of a socket into the state storage for an application

• If the application is resumed this information can be used to recreate the

network connection without having to make a new socket

• This information could be stored in isolated storage if you wanted to make the

application re-establish the connection when it is launched•Need to be mindful of timeouts in this situation

Persisting connection information

PhoneApplicationService.Current.State["RemoteHostName"] = socket.Information.RemoteHostName.RawName;PhoneApplicationService.Current.State["RemoteServiceName"] = socket.Information.RemoteServiceName;


•When the application restarts it can recreate the connection by using the

storage names

• Both of the parties in the socket based connection should use this to allow

them to recover network connections

•However, this option is not present on Windows 8, only on Windows Phone 8

Recreating a Socket

string storedRemoteHostRawName = PhoneApplicationService.Current.State["RemoteHostName"] as string;string storedRemoteServiceName = PhoneApplicationService.Current.State["RemoteServiceName"] as string;

HostName newRemoteHostName = new HostName(storedRemoteHostRawName);

await socket.ConnectAsync(newRemoteHostName, storedRemoteServiceName);

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• Bluetooth and Near Field Communications (NFC) allow two Windows Phones to

create connections to each other and other devices

• To connection a Bluetooth device it must be paired with the phone and support

the service that the application requests

• Two applications can discover each other and exchange messages without

pairing

• The connection provided is surfaced as a StreamSocket

•NFC allows a phone to exchange small amounts of data with another phone or

device

•Windows Phone 8 provides a means by which an NFC message can be used to

instigate a StreamSocket connection over Bluetooth or WiFi between two

devices

• Applications can store socket properties that allow connections to be resumed

quickly if the program is made dormant or tombstoned.

Summary

The information herein is for informational purposes only an represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be

interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation.

© 2012 Microsoft Corporation.

All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.

MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

Technology

Windows Phone 8 - 13 Near Field Communcations and Bluetooth