/// <summary>
/// Closes the device, stops the device watcher, stops listening for app events, and resets object state to before a device
/// was ever connected.
///
/// When the UsbDevice is closing, it will cancel all IO operations that are still pending (not complete).
/// The close will not wait for any IO completion callbacks to be called, so the close call may complete before any of
/// the IO completion callbacks are called.
/// The pending IO operations will still call their respective completion callbacks with either a task
/// canceled error or the operation completed.
/// </summary>
private void CloseCurrentlyConnectedDevice()
{
if (device != null)
{
// Notify callback that we're about to close the device
deviceCloseCallback?.Invoke(this, deviceInformation);
Debug.WriteLine($"Closing device {deviceInformation.Id}");
// This closes the handle to the device
device.Dispose();
device = null;
}
}
/// <summary>
/// This method opens the device using the WinRT Usb API. After the device is opened, save the device
/// so that it can be used across scenarios.
///
/// It is important that the FromIdAsync call is made on the UI thread because the consent prompt can only be displayed
/// on the UI thread.
///
/// This method is used to reopen the device after the device reconnects to the computer and when the app resumes.
/// </summary>
/// <param name="deviceInfo">Device information of the device to be opened</param>
/// <param name="deviceSelector">The AQS used to find this device</param>
/// <returns>True if the device was successfully opened, false if the device could not be opened for well known reasons.
/// An exception may be thrown if the device could not be opened for extraordinary reasons.</returns>
public async Task <bool> OpenDeviceAsync(DeviceInformation deviceInfo, String deviceSelector)
{
device = await Windows.Devices.Usb.UsbDevice.FromIdAsync(deviceInfo.Id);
bool successfullyOpenedDevice = false;
try
{
// Device could have been blocked by user or the device has already been opened by another app.
if (device != null)
{
successfullyOpenedDevice = true;
deviceInformation = deviceInfo;
this.deviceSelector = deviceSelector;
Debug.WriteLine($"Device {deviceInformation.Id} opened");
// Notify registered callback handle that the device has been opened
deviceConnectedCallback?.Invoke(this, deviceInformation);
// Background tasks are not part of the app, so app events will not have an affect on the device
if (!isBackgroundTask && (appSuspendEventHandler == null || appResumeEventHandler == null))
{
RegisterForAppEvents();
}
// User can block the device after it has been opened in the Settings charm. We can detect this by registering for the
// DeviceAccessInformation.AccessChanged event
if (deviceAccessEventHandler == null)
{
RegisterForDeviceAccessStatusChange();
}
// Create and register device watcher events for the device to be opened unless we're reopening the device
if (deviceWatcher == null)
{
deviceWatcher = DeviceInformation.CreateWatcher(deviceSelector);
RegisterForDeviceWatcherEvents();
}
if (!watcherStarted)
{
// Start the device watcher after we made sure that the device is opened.
StartDeviceWatcher();
}
}
else
{
successfullyOpenedDevice = false;
//notificationStatus = NotifyType.ErrorMessage;
var deviceAccessStatus = DeviceAccessInformation.CreateFromId(deviceInfo.Id).CurrentStatus;
switch (deviceAccessStatus)
{
case DeviceAccessStatus.DeniedByUser:
Debug.WriteLine($"Access to the device was blocked by the user : {deviceInfo.Id}");
break;
case DeviceAccessStatus.DeniedBySystem:
// This status is most likely caused by app permissions (did not declare the device in the app's package.appxmanifest)
// This status does not cover the case where the device is already opened by another app.
Debug.WriteLine($"Access to the device was blocked by the system : {deviceInfo.Id}");
break;
default:
// Most likely the device is opened by another app, but cannot be sure
Debug.WriteLine($"Unknown error, possibly opened by another app : {deviceInfo.Id}");
break;
}
}
}
// catch all because the device open might fail for a number of reasons
catch { }
return(successfullyOpenedDevice);
}
