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Getting started with Point of Service

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Point of service, point of sale, or Point of Service devices are computer peripherals used to facilitate retail transactions. Examples of Point of Service devices include electronic cash registers, barcode scanners, magnetic stripe readers, and receipt printers.

Here you’ll learn the basics of interfacing with Point of Service devices by using the Windows Runtime Point of Service APIs. We’ll cover device enumeration, checking device capabilities, claiming devices, and device sharing. We use a barcode scanner device as an example, but almost all the guidance here applies to any UWP-compatible Point of Service device. (For a list of supported devices, see Point of Service device support).

Finding and connecting to Point of Service peripherals

Before a Point of Service device can be used by an app, it must be paired with the PC where the app is running. There are several ways to connect to Point of Service devices, either programmatically or through the Settings app.

Connecting to devices by using the Settings app

When you plug a Point of Service device like a barcode scanner into a PC, it shows up just like any other device. You can find it in the Devices > Bluetooth & other devices section of the Settings app. There you can pair with a Point of Service device by selecting Add Bluetooth or other device.

Some Point of Service devices may not appear in the Settings app until they are programmatically enumerated by using the Point of Service APIs.

Getting a single Point of Service device with GetDefaultAsync

In a simple use case, you may have just one Point of Service peripheral connected to the PC where the app is running and want to set it up as quickly as possible. To do that, retrieve the “default” device with the GetDefaultAsync method as shown here.

using Windows.Devices.PointOfService;

BarcodeScanner barcodeScanner = await BarcodeScanner.GetDefaultAsync();

If the default device is found, the device object retrieved is ready to be claimed. “Claiming” a device gives an application exclusive access to it, preventing conflicting commands from multiple processes.

Note

If more than one Point of Service device is connected to the PC, GetDefaultAsync returns the first device it finds. For this reason, use FindAllAsync unless you’re sure that only one Point of Service device is visible to the application.

Enumerating a collection of devices with FindAllAsync

When connected to more than one device, you must enumerate the collection of PointOfService device objects to find the one you want to claim. For example, the following code creates a collection of all the barcode scanners currently connected, and then searches the collection for a scanner with a specific name.

using Windows.Devices.Enumeration;
using Windows.Devices.PointOfService;

string selector = BarcodeScanner.GetDeviceSelector();       
DeviceInformationCollection deviceCollection = await DeviceInformation.FindAllAsync(selector);

foreach (DeviceInformation devInfo in deviceCollection)
{
    Debug.WriteLine("{0} {1}", devInfo.Name, devInfo.Id);
    if (devInfo.Name.Contains("1200G"))
    {
        Debug.WriteLine(" Found one");
    }
}

Scoping the device selection

When connecting to a device, you may want to limit your search to a subset of Point of Service peripherals that your app has access to. Using the GetDeviceSelector method, you can scope the selection to retrieve devices connected only by a certain method (Bluetooth, USB, etc.). You can create a selector that searches for devices over Bluetooth, IP, Local, or All connection types. This can be useful, as wireless device discovery takes a long time compared to local (wired) discovery. You can ensure a deterministic wait time for local device connection by limiting FindAllAsync to Local connection types. For example, this code retrieves all barcode scanners accessible via a local connection.

string selector = BarcodeScanner.GetDeviceSelector(PosConnectionTypes.Local);
DeviceInformationCollection deviceCollection = await DeviceInformation.FindAllAsync(selector);

Reacting to device connection changes with DeviceWatcher

As your app runs, sometimes devices will be disconnected or updated, or new devices will need to be added. You can use the DeviceWatcher class to access device-related events, so your app can respond accordingly. Here’s example of how to use DeviceWatcher, with method stubs to be called if a device is added, removed, or updated.

DeviceWatcher deviceWatcher = DeviceInformation.CreateWatcher(selector);
deviceWatcher.Added += DeviceWatcher_Added;
deviceWatcher.Removed += DeviceWatcher_Removed;
deviceWatcher.Updated += DeviceWatcher_Updated;

void DeviceWatcher_Added(DeviceWatcher sender, DeviceInformation args)
{
    // TODO: Add the DeviceInformation object to your collection
}

void DeviceWatcher_Removed(DeviceWatcher sender, DeviceInformationUpdate args)
{
    // TODO: Remove the item in your collection associated with DeviceInformationUpdate
}

void DeviceWatcher_Updated(DeviceWatcher sender, DeviceInformationUpdate args)
{
    // TODO: Update your collection with information from DeviceInformationUpdate
}

Checking the capabilities of a Point of Service device

Even within a device class, such as barcode scanners, the attributes of each device may vary considerably between models. If your app requires a specific device attribute, you may need to inspect each connected device object to determine whether the attribute is supported. For example, perhaps your business requires that labels be created using a specific barcode printing pattern. Here’s how you could check to see whether a connected barcode scanner supports a symbology.

Note

A symbology is the language mapping that a barcode uses to encode messages.

try
{
    BarcodeScanner barcodeScanner = await BarcodeScanner.FromIdAsync(deviceId);
    if (await barcodeScanner.IsSymbologySupportedAsync(BarcodeSymbologies.Code32))
    {
        Debug.WriteLine("Has symbology");
    }
}
catch (Exception ex)
{
    Debug.WriteLine("FromIdAsync() - " - ex.Message);
}

Using the Device.Capabilities class

The Device.Capabilities class is an attribute of all Point of Service device classes and can be used to get general information about each device. For example, this example determines whether a device supports statistics reporting and, if it does, retrieves statistics for any types supported.

try
{
    if (barcodeScanner.Capabilities.IsStatisticsReportingSupported)
    {
        Debug.WriteLine("Statistics reporting is supported");

        string[] statTypes = new string[] {""};
        IBuffer ibuffer = await barcodeScanner.RetrieveStatisticsAsync(statTypes);
    }
}
catch (Exception ex)
{
    Debug.WriteLine("EX: RetrieveStatisticsAsync() - " - ex.Message);
}

Claiming a Point of Service device

Before you can use a Point of Service device for active input or output, you must claim it, granting the application exclusive access to many of its functions. This code shows how to claim a barcode scanner device, after you’ve found the device by using one of the methods described earlier.

try
{
    claimedBarcodeScanner = await barcodeScanner.ClaimScannerAsync();
}
catch (Exception ex)
{
    Debug.WriteLine("EX: ClaimScannerAsync() - " - ex.Message);
}

Retaining the device

When using a Point of Service device over a network or Bluetooth connection, you may wish to share the device with other apps on the network. (For more info about this, see Sharing Devices.) In other cases, you may want to hold on to the device for prolonged use. This example shows how to retain a claimed barcode scanner after another app has requested that the device be released.

claimedBarcodeScanner.ReleaseDeviceRequested += claimedBarcodeScanner_ReleaseDeviceRequested;

void claimedBarcodeScanner_ReleaseDeviceRequested(object sender, ClaimedBarcodeScanner e)
{
    e.RetainDevice();  // Retain exclusive access to the device
}

Input and output

After you’ve claimed a device, you’re almost ready to use it. To receive input from the device, you must set up and enable a delegate to receive data. In the example below, we claim a barcode scanner device, set its decode property, and then call EnableAsync to enable decoded input from the device. This process varies between device classes, so for guidance about how to set up a delegate for non-barcode devices, refer to the relevant UWP app sample.

try
{
    claimedBarcodeScanner = await barcodeScanner.ClaimScannerAsync();
    if (claimedBarcodeScanner != null)
    {
        claimedBarcodeScanner.DataReceived += claimedBarcodeScanner_DataReceived;
        claimedBarcodeScanner.IsDecodeDataEnabled = true;
        await claimedBarcodeScanner.EnableAsync();
    }
}
catch (Exception ex)
{
    Debug.WriteLine("EX: ClaimScannerAsync() - " - ex.Message);
}


void claimedBarcodeScanner_DataReceived(ClaimedBarcodeScanner sender, BarcodeScannerDataReceivedEventArgs args)
{
    string symbologyName = BarcodeSymbologies.GetName(args.Report.ScanDataType);
    var scanDataLabelReader = DataReader.FromBuffer(args.Report.ScanDataLabel);
    string barcode = scanDataLabelReader.ReadString(args.Report.ScanDataLabel.Length);
}

Sharing a device between apps

Point of Service devices are often used in cases where more than one app will need to access them in a brief period. A device can be shared when connected to multiple apps locally (USB or other wired connection), or through a Bluetooth or IP network. Depending on the needs of each app, one process may need to dispose of its claim on the device. This code disposes of our claimed barcode scanner device, allowing other apps to claim and use it.

if (claimedBarcodeScanner != null)
{
    claimedBarcodeScanner.Dispose();
    claimedBarcodeScanner = null;
}

Note

Both the claimed and unclaimed Point of Service device classes implement the IClosable interface. If a device is connected to an app via network or Bluetooth, both the claimed and unclaimed objects must be disposed of before another app can connect.

See also