/// <summary>
/// Specifies a callback when properties change.
/// </summary>
/// <param name="callback">The callback.</param>
/// <param name="publisher">The publisher.</param>
/// <param name="propertyNames">The property names.</param>
internal static void WhenChanged(this Action callback, INotifyPropertyChanged publisher, params string[] propertyNames)
{
var bindPropertyChanged = false;
lock (SyncLock)
{
// Create the subscription set for the publisher if it does not exist.
if (Subscriptions.ContainsKey(publisher) == false)
{
Subscriptions[publisher] = new SubscriptionSet();
// if it did not exist before, we need to bind to the
// PropertyChanged event of the publisher.
bindPropertyChanged = true;
}
// Save the Action reference so that the weak reference is not lost
// TODO: The references will never be detected as dead if we pin them
// but for the purposes of this sample app we don't need to remove the
// dead references.
PinnedActions[callback] = true;
foreach (var propertyName in propertyNames)
{
// Create the set of callback references for the publisher's property if it does not exist.
if (Subscriptions[publisher].ContainsKey(propertyName) == false)
{
Subscriptions[publisher][propertyName] = new CallbackReferenceSet();
}
// Add the callback for the publisher's property changed
Subscriptions[publisher][propertyName].Add(new CallbackReference(callback));
}
}
// No need to bind to the PropertyChanged event if we are already bound to it.
if (bindPropertyChanged == false)
{
return;
}
// Finally, bind to property changed
publisher.PropertyChanged += (s, e) =>
{
var deadCallbacks = new CallbackReferenceSet();
var aliveCallbacks = new CallbackReferenceSet();
lock (SyncLock)
{
// we don't need to perform any action if there are no subscriptions to
// this property name.
if (Subscriptions[publisher].ContainsKey(e.PropertyName) == false)
{
return;
}
// Get the list of alive subscriptions for this property name
aliveCallbacks.AddRange(Subscriptions[publisher][e.PropertyName]);
}
// Call the subscription's callbacks
foreach (var aliveSubscription in aliveCallbacks)
{
// Check if the subscription reference is alive.
if (aliveSubscription.IsAlive == false)
{
deadCallbacks.Add(aliveSubscription);
continue;
}
// if the subscription is alive, invoke the matching action
aliveSubscription.Target?.Invoke();
}
// Skip over if we don't have dead subscriptions
if (deadCallbacks.Count == 0)
{
return;
}
// Remove dead subscriptions
lock (SyncLock)
{
foreach (var deadSubscriber in deadCallbacks)
{
Subscriptions[publisher][e.PropertyName].Remove(deadSubscriber);
}
}
};
}
internal static void WhenChanged(this Action callback, bool pinned, INotifyPropertyChanged publisher, params string[] propertyNames)
{
var bindPropertyChanged = false;
using (Locker.AcquireWriterLock())
{
if (Subscriptions.ContainsKey(publisher) == false)
{
Subscriptions[publisher] = new SubscriptionSet();
bindPropertyChanged = true;
}
// Save the Action reference so that the weak reference is not lost
if (pinned)
{
PinnedActions[callback] = true;
}
foreach (var propertyName in propertyNames)
{
if (Subscriptions[publisher].ContainsKey(propertyName) == false)
{
Subscriptions[publisher][propertyName] = new CallbackReferenceSet();
}
Subscriptions[publisher][propertyName].Add(new CallbackReference(callback));
}
}
if (bindPropertyChanged == false)
{
return;
}
// Finally, bind to property changed
publisher.PropertyChanged += (s, e) =>
{
if (Subscriptions[publisher].ContainsKey(e.PropertyName) == false)
{
return;
}
var deadCallbacks = new CallbackReferenceSet();
var aliveCallbacks = new CallbackReferenceSet();
using (Locker.AcquireReaderLock())
{
aliveCallbacks.AddRange(Subscriptions[publisher][e.PropertyName]);
}
foreach (var aliveSubscription in aliveCallbacks)
{
if (aliveSubscription.IsAlive == false)
{
deadCallbacks.Add(aliveSubscription);
continue;
}
aliveSubscription.Target?.Invoke();
}
if (deadCallbacks.Count == 0)
{
return;
}
using (Locker.AcquireWriterLock())
{
foreach (var deadSubscriber in deadCallbacks)
{
Subscriptions[publisher][e.PropertyName].Remove(deadSubscriber);
}
}
};
}