How to display printer status in a UWP device app

In Windows 8.1, users can check their printer status from the modern UI of a UWP device app. This topic uses the C# version of the Print settings and print notifications sample to demonstrate how to query the printer status and display it. To learn more about UWP device apps in general, see Meet UWP device apps.

The C# version of the Print settings and print notifications sample uses the InkLevel.xaml page to demonstrate how to get the printer status (in this case, the ink level) and display it. A print helper class is used to create a device context (IPrinterExtensionContext) and perform the device queries. The PrinterHelperClass.cs file is in the DeviceAppForPrintersLibrary project and uses APIs defined in the PrinterExtensionLibrary project. The printer extension library provides a convenient way to access the printer extension interfaces of the v4 print driver. For more info, see the Printer extension library overview.

Prerequisites

Before you get started:

1. Make sure your printer is installed using a v4 print driver. For more info, see Developing v4 print drivers.

2. Get your development PC set up. See Getting started for info about downloading the tools and creating a developer account.

3. Associate your app with the store. See Step 1: Create a UWP device app for info about that.

4. Create device metadata for your printer that associates it with your app. See Step 2: Create device metadata for more about that.

5. If you're writing you're writing your app with C# or JavaScript, add the PrinterExtensionLibrary and DeviceAppForPrintersLibrary projects to your UWP device app solution. You can find each of these projects in the Print settings and print notifications sample.

   Note

   Because C++ can access COM directly, C++ apps do not require a separate library to work with the COM-based printer device context.

Step 1: Find the printer

Before a device context can be created, the app needs to determine the device ID of the printer. To do this, the sample uses the EnumerateAssociatedPrinters method to search through all printers that are attached to the PC. Then it checks the container for each printer and looks for an association by comparing each container's PackageFamilyName property.

This example shows the EnumerateAssociatedPrinters method from the InkLevel.xaml.cs file:

async void EnumerateAssociatedPrinters(object sender, RoutedEventArgs e)
{
    // Reset output text and associated printer array.
    AssociatedPrinters.Items.Clear();
    BidiOutput.Text = "";

    // GUID string for printers.
    string printerInterfaceClass = "{0ecef634-6ef0-472a-8085-5ad023ecbccd}";
    string selector = "System.Devices.InterfaceClassGuid:=\"" + printerInterfaceClass + "\"";

    // By default, FindAllAsync does not return the containerId for the device it queries.
    // We have to add it as an additional property to retrieve. 
    string containerIdField = "System.Devices.ContainerId";
    string[] propertiesToRetrieve = new string[] { containerIdField };

    // Asynchronously find all printer devices.
    DeviceInformationCollection deviceInfoCollection = await DeviceInformation.FindAllAsync(selector, propertiesToRetrieve);

    // For each printer device returned, check if it is associated with the current app.
    for (int i = 0; i < deviceInfoCollection.Count; i++)
    {
        DeviceInformation deviceInfo = deviceInfoCollection[i];
        FindAssociation(deviceInfo, deviceInfo.Properties[containerIdField].ToString());
    }
}

The FindAssociation method, called by EnumerateAssociatedPrinters, checks if a printer is associated with the current application. In other words, this method checks if the app is a UWP device app. This association exists when the app and printer are defined in device metadata on the local PC.

This example shows the FindAssociation method from the InkLevel.xaml.cs file:

async void FindAssociation(DeviceInformation deviceInfo, string containerId)
{

    // Specifically telling CreateFromIdAsync to retrieve the AppPackageFamilyName. 
    string packageFamilyName = "System.Devices.AppPackageFamilyName";
    string[] containerPropertiesToGet = new string[] { packageFamilyName };

    // CreateFromIdAsync needs braces on the containerId string.
    string containerIdwithBraces = "{" + containerId + "}";

    // Asynchronously getting the container information of the printer.
    PnpObject containerInfo = await PnpObject.CreateFromIdAsync(PnpObjectType.DeviceContainer, containerIdwithBraces, containerPropertiesToGet);

    // Printers could be associated with other device apps, only the ones with package family name
    // matching this app's is associated with this app. The packageFamilyName for this app will be found in this app's packagemanifest
    string appPackageFamilyName = "Microsoft.SDKSamples.DeviceAppForPrinters.CS_8wekyb3d8bbwe";
    var prop = containerInfo.Properties;

    // If the packageFamilyName of the printer container matches the one for this app, the printer is associated with this app.
    string[] packageFamilyNameList = (string[])prop[packageFamilyName];
    if (packageFamilyNameList != null)
    {
        for (int j = 0; j < packageFamilyNameList.Length; j++)
        {
            if (packageFamilyNameList[j].Equals(appPackageFamilyName))
            {
                AddToList(deviceInfo);
            }
        }
    }
}

When an association is found, the FindAssociation method uses the AddToList method to add the device ID to a list of associated device IDs. These IDs are stored in a ComboBox named AssociatedPrinters.

This example shows the AddToList method from the InkLevel.xaml.cs file:

void AddToList(DeviceInformation deviceInfo)
{
    // Creating a new display item so the user sees the friendly name instead of the interfaceId.
    ComboBoxItem item = new ComboBoxItem();
    item.Content = deviceInfo.Properties["System.ItemNameDisplay"] as string;
    item.DataContext = deviceInfo.Id;
    AssociatedPrinters.Items.Add(item);

    // If this is the first printer to be added to the combo box, select it.
    if (AssociatedPrinters.Items.Count == 1)
    {
        AssociatedPrinters.SelectedIndex = 0;
    }
}

Step 2: Display the status

The GetInkStatus method uses an asynchronous event-based pattern to request information from the printer. This method uses an associated device ID to get a device context that can be used to get device status. The call to the printHelper.SendInkLevelQuery() method initiates the device query. When the response returns, the OnInkLevelReceived method is called and the UI is updated.

This example shows the GetInkStatus and OnInkLevelReceived methods from the InkLevel.xaml.cs file:

void GetInkStatus(object sender, RoutedEventArgs e)
{
    if (AssociatedPrinters.Items.Count > 0)
    {
        // Get the printer that the user has selected to query.
        ComboBoxItem selectedItem = AssociatedPrinters.SelectedItem as ComboBoxItem;

        // The interfaceId is retrieved from the detail field.
        string interfaceId = selectedItem.DataContext as string;

        try
        {
            // Unsubscribe existing ink level event handler, if any.
            if (printHelper != null)
            {
                printHelper.OnInkLevelReceived -= OnInkLevelReceived;
                printHelper = null;
            }

            object context = Windows.Devices.Printers.Extensions.PrintExtensionContext.FromDeviceId(interfaceId);printHelper.SendInkLevelQuery()

            // Use the PrinterHelperClass to retrieve the bidi data and display it.
            printHelper = new PrintHelperClass(context);
            try
            {
                printHelper.OnInkLevelReceived += OnInkLevelReceived;
                printHelper.SendInkLevelQuery();

                rootPage.NotifyUser("Ink level query successful", NotifyType.StatusMessage);
            }
            catch (Exception)
            {
                rootPage.NotifyUser("Ink level query unsuccessful", NotifyType.ErrorMessage);
            }
        }
        catch (Exception)
        {
            rootPage.NotifyUser("Error retrieving PrinterExtensionContext from InterfaceId", NotifyType.ErrorMessage);
        }
    }
}

private void OnInkLevelReceived(object sender, string response)
{
    BidiOutput.Text = response;
}

The print helper class takes care of sending the Bidi query to the device and receiving the response.

This example shows the SendInkLevelQuery method, and others, from the PrintHelperClass.cs file. Note that only some of the print helper class methods are shown here. Download the Print settings and print notifications sample to see the full code.

public void SendInkLevelQuery()
{
    printerQueue.OnBidiResponseReceived += OnBidiResponseReceived;

    // Send the query.
    string queryString = "\\Printer.Consumables";
    printerQueue.SendBidiQuery(queryString);
}

private void OnBidiResponseReceived(object sender, PrinterQueueEventArgs responseArguments)
{
    // Invoke the ink level event with appropriate data.
    dispatcher.RunAsync(
        Windows.UI.Core.CoreDispatcherPriority.Normal,
        () =>
        {
            OnInkLevelReceived(sender, ParseResponse(responseArguments));
        });
}

private string ParseResponse(PrinterQueueEventArgs responseArguments)
{
    if (responseArguments.StatusHResult == (int)HRESULT.S_OK)
        return responseArguments.Response;
    else
        return InvalidHResult(responseArguments.StatusHResult);
}

private string InvalidHResult(int result)
{
    switch (result)
    {
        case unchecked((int)HRESULT.E_INVALIDARG):
            return "Invalid Arguments";
        case unchecked((int)HRESULT.E_OUTOFMEMORY):
            return "Out of Memory";
        case unchecked((int)HRESULT.ERROR_NOT_FOUND):
            return "Not found";
        case (int)HRESULT.S_FALSE:
            return "False";
        case (int)HRESULT.S_PT_NO_CONFLICT:
            return "PT No Conflict";
        default:
            return "Undefined status: 0x" + result.ToString("X");
    }
}

Testing

Before you can test your UWP device app, it must be linked to your printer using device metadata.

You need a copy of the device metadata package for your printer, to add the device app info to it. If you don't have device metadata, you can build it using the Device Metadata Authoring Wizard as described in the topic Step 2: Create device metadata for your UWP device app.

The following steps build your app and install the device metadata.

1. Enable test signing.

   1. Start the Device Metadata Authoring Wizard from %ProgramFiles(x86)%\Windows Kits\8.1\bin\x86, by double-clicking DeviceMetadataWizard.exe

   2. From the Tools menu, select Enable Test Signing.

2. Reboot the computer

3. Build the solution by opening the solution (.sln) file. Press F7 or go to Build->Build Solution from the top menu after the sample has loaded.

4. Disconnect and uninstall the printer. This step is required so that Windows will read the updated device metadata the next time the device is detected.

5. Edit and save device metadata. To link the device app to your device, you must associate the device app with your device.

   Note

   If you haven't created your device metadata yet, see Step 2: Create device metadata for your UWP device app.

   1. If the Device Metadata Authoring Wizard is not open yet, start it from %ProgramFiles(x86)%\Windows Kits\8.1\bin\x86, by double-clicking DeviceMetadataWizard.exe.

   2. Click Edit Device Metadata. This will let you edit your existing device metadata package.

   3. In the Open dialog box, locate the device metadata package associated with your UWP device app. (It has a devicemetadata-ms file extension.)

   4. On the Specify UWP device app information page, enter the Microsoft Store app info in the UWP device app box. Click on Import UWP app manifest file to automatically enter the Package name, Publisher name, and UWP app ID.

   5. If your app is registering for printer notifications, fill out the Notification handlers box. In Event ID, enter the name of the print event handler. In Event Asset, enter the name of the file where that code resides.

   6. When you're done, click Next until you get to the Finish page.

   7. On the Review the device metadata package page, make sure that all of the settings are correct and select the Copy the device metadata package to the metadata store on the local computer check box. Then click Save.

6. Reconnect your printer so that Windows reads the updated device metadata when the device is connected.

Troubleshooting

Issue: Can't find printer when enumerating devices associated with the app

If your printer isn't found when enumerating the associated printers:

• Possible cause: Test signing is not turned on. See the Debugging section in this topic for info about turning it on.

• Possible cause: The app is not querying for the right Package Family Name. Check the Package Family Name in your code. Open up package.appxmanifest in Microsoft Visual Studio and make sure that the package family name you are querying for matches the one in the Packaging tab, in the Package Family Name field.

• Possible cause: The device metadata is not associated with the Package Family Name. Use the Device Metadata Authoring Wizard to open the device metadata and check the package family name. Start the wizard from %ProgramFiles(x86)%\Windows Kits\8.1\bin\x86, by double-clicking DeviceMetadataWizard.exe.

Issue: Found printer associated with the app, but can't query Bidi info

If your printer was found when enumerating the associated printers, but a Bidi query returns an error...

• Possible cause: Wrong package family name. Check the Package Family Name in your code. Open up package.appxmanifest in Visual Studio and make sure that the package family name you are querying for matches the one in the Packaging tab, in the Package Family Name field.

• Possible cause: Printer was installed using a v3 printer, rather than a v4 printer. To see which version is installed, open PowerShell and type the following command:

  get-printer | Select Name, {(get-printerdriver -Name $_.DriverName).MajorVersion}
  

Related topics

Developing v4 print drivers

Printer Extension Interfaces (v4 Print Driver)

Bidirectional Communications

Getting started with UWP apps

Create a UWP device app (step-by-step guide)

Create device metadata for a UWP device app (step-by-step guide)