I am trying to build an app using the C# POS printer API.
I successfully ran the sample app provided here: https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/PosPrinter, and now I am trying to integrate the API into my own UWP application.
This is what I have so far:
public class PrinterManager
{
private PosPrinter printer = null;
private ClaimedPosPrinter claimedPrinter = null;
private bool printerClaimed = false;
public PrinterManager()
{
}
public async void EnablePrinter()
{
//find printer
printer = await PrinterHelper.GetFirstReceiptPrinterAsync();
//claim printer
printerClaimed = (claimedPrinter = await printer.ClaimPrinterAsync()) != null;
}
...
}
printerHelper.cs:
class PrinterHelper
{
public static async Task<T> GetFirstDeviceAsync<T>(string selector, Func<string, Task<T>> convertAsync)
where T : class
{
var completionSource = new TaskCompletionSource<T>();
var pendingTasks = new List<Task>();
DeviceWatcher watcher = DeviceInformation.CreateWatcher(selector);
watcher.Added += (DeviceWatcher sender, DeviceInformation device) =>
{
Func<string, Task> lambda = async (id) =>
{
T t = await convertAsync(id);
if (t != null)
{
completionSource.TrySetResult(t);
}
};
pendingTasks.Add(lambda(device.Id));
};
watcher.EnumerationCompleted += async (DeviceWatcher sender, object args) =>
{
// Wait for completion of all the tasks we created in our "Added" event handler.
await Task.WhenAll(pendingTasks);
// This sets the result to "null" if no task was able to produce a device.
completionSource.TrySetResult(null);
};
watcher.Start();
// Wait for enumeration to complete or for a device to be found.
T result = await completionSource.Task;
watcher.Stop();
return result;
}
// By default, use all connections types.
public static async Task<PosPrinter> GetFirstReceiptPrinterAsync(PosConnectionTypes connectionTypes = PosConnectionTypes.All)
{
return await GetFirstDeviceAsync(PosPrinter.GetDeviceSelector(connectionTypes),
async (id) =>
{
PosPrinter printer = await PosPrinter.FromIdAsync(id);
if (printer != null && printer.Capabilities.Receipt.IsPrinterPresent)
{
return printer;
}
// Dispose the unwanted printer.
printer?.Dispose();
return null;
});
}
}
I call EnablePrinter()
, and my application runs without exceptions, but the printer remains null
after the printer = await PrinterHelper.GetFirstReceiptPrinterAsync();
line is executed.
It turns out that the problem was quite stupid:
I needed to go to Package.appxmanifest --> Capabilities and enable "Point of Service".