/// <summary>
/// Occurs when a property on the monitored class changes
/// </summary>
/// <param name="sender">Object that fired the notification</param>
/// <param name="propertyChangedEventArgs">Details about the event</param>
private static void SelfOnPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
{
var self = (INotifyPropertyChanged)sender;
TaskCompletionSource <bool> completionSource;
if (!self.TaskCompleted(out completionSource))
{
return;
}
completionSource?.SetResult(true);
CompletionSources.Remove(self);
self.PropertyChanged -= SelfOnPropertyChanged;
}
/// <summary>
/// Check if the task has been completed
/// </summary>
/// <param name="self">Class instance that contains the properties</param>
/// <param name="completionSource">Completion source that was used to create the monitored task</param>
/// <returns>True - Task completed, otherwise false</returns>
private static bool TaskCompleted(this INotifyPropertyChanged self,
out TaskCompletionSource <bool> completionSource)
{
var taskCompleted = true;
var properties = self.GetBlockingProperties();
completionSource = CompletionSources.ContainsKey(self) ? CompletionSources[self] : null;
foreach (var property in properties)
{
var attribute = property.GetCustomAttribute <BlockingPropertyAttribute>();
if (!property.GetValue(self).Equals(attribute.ExpectedValue))
{
taskCompleted = false;
}
}
return(taskCompleted);
}
/// <summary>
/// Returns a task that can be blocked against until a specific property changes.
/// The property or properties should be marked with <see cref="BlockingPropertyAttribute"/> otherwise a completed task will be returned immediately.
/// </summary>
/// <param name="self">Class instance that contains the properties</param>
/// <returns>Task that can be awaited until the decorated properties change</returns>
public static Task <bool> BlockUntil(this INotifyPropertyChanged self)
{
TaskCompletionSource <bool> completionSource;
if (self.TaskCompleted(out completionSource))
{
// The task is already finished
return(Task.FromResult(true));
}
completionSource = new TaskCompletionSource <bool>();
if (!CompletionSources.ContainsKey(self))
{
CompletionSources.Add(self, completionSource);
}
self.PropertyChanged += SelfOnPropertyChanged;
return(completionSource.Task);
}