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PORoutedUICommand PreviewExecuted Bug?
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copied!<p>I'm building an application using the MVVM design pattern and I want to make use of the RoutedUICommands defined in the ApplicationCommands class. Since the CommandBindings property of a View (read UserControl) isn't a DependencyProperty we can't bind CommandBindings defined in a ViewModel to the View directly. I solved this by defining an abstract View class which binds this programmatically, based on a ViewModel interface which ensures every ViewModel has an ObservableCollection of CommandBindings. This all works fine, however, in some scenarios I want to execute logic which is defined in different classes (the View and ViewModel) same command. For instance, when saving a document.</p> <p>In the ViewModel the code saves the document to disk:</p> <pre><code>private void InitializeCommands() { CommandBindings = new CommandBindingCollection(); ExecutedRoutedEventHandler executeSave = (sender, e) => { document.Save(path); IsModified = false; }; CanExecuteRoutedEventHandler canSave = (sender, e) => { e.CanExecute = IsModified; }; CommandBinding save = new CommandBinding(ApplicationCommands.Save, executeSave, canSave); CommandBindings.Add(save); } </code></pre> <p>At first sight the previous code is all I wanted to do, but the TextBox in the View to which the document is bound, only updates its Source when it loses its focus. However, I can save a document without losing focus by pressing Ctrl+S. This means the document is saved before the changes where Updated in the source, effectively ignoring the changes. But since changing the UpdateSourceTrigger to PropertyChanged isn't a viable option for performance reasons, something else must force an update before saving. So I thought, lets use the PreviewExecuted event to force the update in the PreviewExecuted event, like so:</p> <pre><code>//Find the Save command and extend behavior if it is present foreach (CommandBinding cb in CommandBindings) { if (cb.Command.Equals(ApplicationCommands.Save)) { cb.PreviewExecuted += (sender, e) => { if (IsModified) { BindingExpression be = rtb.GetBindingExpression(TextBox.TextProperty); be.UpdateSource(); } e.Handled = false; }; } } </code></pre> <p>However, assigning an handler to the PreviewExecuted event seems to cancel the event altogether, even when I explicitly set the Handled property to false. So the executeSave eventhandler I defined in the previous code sample isn't executed anymore. Note that when I change the cb.PreviewExecuted to cb.Executed both pieces of code <strong>do</strong> execute, but not in the correct order.</p> <p>I think this is a Bug in .Net, because you should be able to add a handler to PreviewExecuted and Executed and have them be executed in order, provided you don't mark the event as handled. </p> <p>Can anyone confirm this behavior? Or am I wrong? Is there a workaround for this Bug?</p>

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