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POHow to convert a WPF Button.Click Event into Observable using Rx and F#
 

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  1. POHow to convert a WPF Button.Click Event into Observable using Rx and F#
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    <p>I am trying to replicate some C# code which creates an <code>IObservable</code> from a <code>Button.Click</code> event. I want to port this code to F#.</p> <p>Here is the original C# code which compiles without errors:</p> <pre><code>Observable.FromEvent&lt;RoutedEventHandler, RoutedEventArgs&gt;( h =&gt; new RoutedEventHandler(h), h =&gt; btn.Click += h, h =&gt; btn.Click -= h)) </code></pre> <p>Here is my failing attempt to do the same in F#:</p> <pre><code>Observable.FromEvent&lt;RoutedEventHandler, RoutedEventArgs&gt;( Func&lt;EventHandler&lt;RoutedEventArgs&gt;, RoutedEventHandler&gt;(fun h -&gt; RoutedEventHandler(h)), Action&lt;RoutedEventHandler&gt;(fun h -&gt; btn.Click.AddHandler h), Action&lt;RoutedEventHandler&gt;(fun h -&gt; btn.Click.RemoveHandler h)) </code></pre> <p>Everything is happy except for the second line of the statement. </p> <p>The F# compiler complains about <code>fun h -&gt; RoutedEventHandler(h)</code> because it doesn't want to except <code>h</code> as a parameter to the <code>RoutedEventHandler</code> constructor.</p> <p>On th other hand the C# compiler seems to have no problem accepting <code>h =&gt; new RoutedEventHandler(h)</code></p> <p>Interestingly enough, in both code samples (C# and F#) the type of <code>h</code> is <code>EventHandler&lt;RoutedEventArgs&gt;</code>.</p> <p>The error message I am getting from the F# compiler is: </p> <blockquote> <p>Error 2 This expression was expected to have type obj -> RoutedEventArgs -> unit but here has type EventHandler </p> </blockquote> <p>The signature for <code>RoutedEventHandler</code> that I found inside PresentationCore is:</p> <p><code>public delegate void RoutedEventHandler(object sender, RoutedEventArgs e);</code></p> <p>As you can see it does take an <code>object</code> and <code>RoutedEventArgs</code> as parameters, so the F# compiler is actually correct. </p> <p>Is there some magic that the C# compiler does behind the scenes to make this work that the F# compiler doesn't or am I just missing something here?</p> <p>Either way, how can I make this work in F#?</p>
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