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copied!<p>Here's my modified version of <a href="https://stackoverflow.com/questions/2764415/how-to-give-the-condition-for-eventtrigger/2823333#2823333">Ray's answer</a>, which creates and attaches dummy events only when the source triggers are set, rather than doing it each time. I thought this would be better for my scenario as I am raising an event on hundreds of items, not just one or two:</p> <pre><code>[ContentProperty("Actions")] public class ConditionalEventTrigger : FrameworkContentElement { static readonly RoutedEvent DummyEvent = EventManager.RegisterRoutedEvent( "", RoutingStrategy.Direct, typeof(EventHandler), typeof(ConditionalEventTrigger)); public static readonly DependencyProperty TriggersProperty = DependencyProperty.RegisterAttached( "Triggers", typeof(ConditionalEventTriggers), typeof(ConditionalEventTrigger), new FrameworkPropertyMetadata(RefreshTriggers)); public static readonly DependencyProperty ConditionProperty = DependencyProperty.Register( "Condition", typeof(bool), typeof(ConditionalEventTrigger)); // the Condition is evaluated whenever an event fires public ConditionalEventTrigger() { Actions = new List<TriggerAction>(); } public static ConditionalEventTriggers GetTriggers(DependencyObject obj) { return (ConditionalEventTriggers)obj.GetValue(TriggersProperty); } public static void SetTriggers(DependencyObject obj, ConditionalEventTriggers value) { obj.SetValue(TriggersProperty, value); } public bool Condition { get { return (bool)GetValue(ConditionProperty); } set { SetValue(ConditionProperty, value); } } public RoutedEvent RoutedEvent { get; set; } public List<TriggerAction> Actions { get; set; } // --- impl ---- // we can't actually fire triggers because WPF won't let us (stupid sealed internal methods) // so, for each trigger, make a dummy trigger (on a dummy event) with the same actions as the real trigger, // then attach handlers for the dummy event public static void RefreshTriggers(DependencyObject obj, DependencyPropertyChangedEventArgs e) { var targetObj = (FrameworkElement)obj; // start by clearing away the old triggers foreach (var t in targetObj.Triggers.OfType<DummyEventTrigger>().ToArray()) targetObj.Triggers.Remove(t); // create and add dummy triggers foreach (var t in ConditionalEventTrigger.GetTriggers(targetObj)) { t.DataContext = targetObj.DataContext; // set and Track DataContext so binding works // targetObj.GetDataContextChanged().WeakSubscribe(dc => t.DataContext = targetObj.DataContext); var dummyTrigger = new DummyEventTrigger { RoutedEvent = DummyEvent }; foreach (var action in t.Actions) dummyTrigger.Actions.Add(action); targetObj.Triggers.Add(dummyTrigger); targetObj.AddHandler(t.RoutedEvent, new RoutedEventHandler((o, args) => { if (t.Condition) // evaluate condition when the event gets fired targetObj.RaiseEvent(new RoutedEventArgs(DummyEvent)); })); } } class DummyEventTrigger : EventTrigger { } } public class ConditionalEventTriggers : List<ConditionalEventTrigger> { } </code></pre> <p>It's used like this:</p> <pre><code><Border> <local:ConditionalEventTrigger.Triggers> <local:ConditionalEventTriggers> <local:ConditionalEventTrigger RoutedEvent="local:ClientEvents.Flash" Condition="{Binding IsFlashing}"> <BeginStoryboard Name="FlashAnimation">... </code></pre> <p>The line</p> <pre><code>// targetObj.GetDataContextChanged().WeakSubscribe(dc => t.DataContext = targetObj.DataContext); </code></pre> <p>is using the reactive framework and some extension methods I wrote, basically we need to subscribe to the <code>.DataContextChanged</code> event of the target object, but we need to do it with a weak reference. If your objects don't ever change their datacontext, then you won't need this code at all</p>

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