/// <summary>
/// If a HidDevice object has been instantiated (a handle to the device is opened), we must close it before the app
/// goes into suspension because the API automatically closes it for us if we don't. When resuming, the API will
/// not reopen the device automatically, so we need to explicitly open the device in the app (Scenario1_DeviceConnect).
///
/// Since we have to reopen the device ourselves when the app resumes, it is good practice to explicitly call the close
/// in the app as well (For every open there is a close).
///
/// We must stop the DeviceWatchers because device watchers will continue to raise events even if
/// the app is in suspension, which is not desired. We resume the device watcher once the app resumes again.
/// </summary>
/// <param name="sender"></param>
/// <param name="eventArgs"></param>
private void OnAppSuspension(Object sender, SuspendingEventArgs args)
{
if (WatchersStarted)
{
watchersSuspended = true;
StopDeviceWatchers();
}
else
{
watchersSuspended = false;
}
DeviceConnect.CloseDevice();
}
/// <summary>
/// When resume into the application, we should reopen a handle to the Hid device again. Please see the comment in
/// OnAppSuspension() for more details why we are doing this.
///
/// See OnAppSuspension for why we are starting the device watchers again
/// </summary>
/// <param name="sender"></param>
/// <param name="arg"></param>
private void OnAppResume(Object sender, Object args)
{
if (watchersSuspended)
{
watchersSuspended = false;
StartDeviceWatchers();
}
// Go to Scenario1_ConnectDevice to see the code for OpenDevice
if (DeviceList.Current.PreviousDeviceId != null)
{
DeviceConnect.OpenDevice(DeviceList.Current.PreviousDeviceId);
}
}
/// <summary>
/// When a device is removed, we need to check if it's the device we're using. If it is, we need to close the device
/// so that all pending operations are canceled properly.
///
/// We will also remove the device from the UI
/// </summary>
/// <param name="sender"></param>
/// <param name="deviceInformationUpdate"></param>
private async void OnDeviceRemoved(DeviceWatcher sender, DeviceInformationUpdate deviceInformationUpdate)
{
if ((DeviceList.Current.IsDeviceConnected) &&
(deviceInformationUpdate.Id == DeviceList.Current.CurrentDeviceEntry.Id))
{
await rootPage.Dispatcher.RunAsync(
CoreDispatcherPriority.Normal,
new DispatchedHandler(() =>
{
rootPage.NotifyUser(
deviceInformationUpdate.Id + " was removed. Don't worry, we are closing the HidDevice",
NotifyType.StatusMessage);
DeviceList.Current.RemoveDeviceFromList(deviceInformationUpdate.Id);
DeviceConnect.CloseDevice();
}));
}
}
/// <summary>
/// Stops all device watchers.
/// </summary>
public void StopDeviceWatchers()
{
rootPage.NotifyUser("Stopping device watchers", NotifyType.StatusMessage);
// Stop all device watchers
foreach (DeviceWatcher deviceWatcher in deviceWatchers)
{
if ((deviceWatcher.Status == DeviceWatcherStatus.Started) ||
(deviceWatcher.Status == DeviceWatcherStatus.EnumerationCompleted))
{
deviceWatcher.Stop();
}
}
// Close the device so we don't have a device connected when the list of devices is empty
DeviceConnect.CloseDevice();
// Clear the list of devices so we don't have potentially disconnected devices around
DeviceList.Current.ClearDeviceEntries();
watchersStarted = false;
}