public async Task Navigate(CancellationToken ct, INavigationRequest request)
{
await Task.Run(async() =>
{
var isReleased = false;
await _semaphore.WaitAsync();
try
{
var pageDefinition = _pageDefinitions.GetPageDefinition(request.PageName);
var viewModel = _viewModelFactory.ResolveViewModel(pageDefinition.ViewModelType);
//create tasks
var setDataContext = SetPageDataContext(pageDefinition, viewModel).ToTask();
var navigatingTask = NotifyNavigating(ct, pageDefinition, request);
var navigationIsStarted = await _dispatcherScheduler.Run(() => _frame.Navigate(pageDefinition.Uri));
if (!navigationIsStarted)
{
throw new InvalidOperationException("Navigation failed");
}
viewModel.Initialize(request);
await navigatingTask;
var pageElement = await setDataContext;
//since the navigation completed, we can let another navigation start
_semaphore.Release();
isReleased = true;
//add entry to history
var historyEntry = new AliveNavigationHistoryEntry(request, viewModel);
_history.Append(historyEntry);
//list to loaded / unloaded events
RegisterViewModelLoad(pageElement, viewModel);
RegisterViewModelUnload(pageElement, viewModel);
}
finally
{
if (!isReleased)
{
_semaphore.Release();
isReleased = true;
}
}
});
}
