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PODouble Click on a WPF ListView - how to fire a command and not use an event handler
 

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    <p>I am a little confused on how to implement an event as a command in my particular situation. I want to honour MVVM, but don't get how in this case.</p> <p>I have a WPF 'view' - viewCustomerSearch. This has some text boxes on it, and when the user clicks 'Search' the results are populated in ListView. viewCustomerSearch is bound to viewmodelCustomerSearch, and it works great.</p> <p>viewCustomerSearch is hosted on viewCustomer.</p> <p>I want to know have viewCustomerSearch expose a custom command - CustomerSelectedCommand - that is 'fired' whenever the ListView in viesCustomerSearch is double clicked, and then handled by the viewmodel behind viewCustomer (which is viewmodelCustomer). This seems the theoretical MVVM pattern implemented correctly.</p> <p>I have broken down the main problem into three smaller problems, but hopefully you can see they are all components of the same challenge.</p> <p><strong>FIRST PROBLEM</strong>: in order to have viewCustomerSearch expose a custom command I seem to have to put this code in viewCustomerSearch - which seems to 'break' MVVM (no code in the view code behind).</p> <pre><code>public readonly DependencyProperty CustomerSelectedCommandProperty = DependencyProperty.Register("CustomerSelectedCommand", typeof(ICommand), typeof(viewCustomerSearch)); public ICommand CustomerSelectedCommand { get { return (ICommand)GetValue(CustomerSelectedCommandProperty); } set { SetValue(CustomerSelectedCommandProperty, value); } } </code></pre> <p><strong>SECOND PROBLEM</strong> (and this is the one that is really getting to me): Best explained by showing what I would do which breaks MVVM. I would have an event handler in the view:</p> <pre><code>private void lstResults_MouseDoubleClick(object sender, MouseButtonEventArgs e) { if (CustomerSelectedCommand != null) CustomerSelectedCommand.Execute(((ViewModels.viewmodelCustomerSearchResult)this.lstResults.SelectedItem).CustomerId); } </code></pre> <p>Well ... I know that you shouldn't put this event handler here; rather it should have a Command to handle it in the viewmodelCustomerSearch. The two problems here are</p> <ul> <li><p>because the 'CustomerSelectedCommand' ICommand is implemented in viewCustomerSearch, viewmodelCustomerSearch can't see it to fire it.</p></li> <li><p>I cannot see how to bind the MouseDoubleClick event to a command, instead of an event handler in the view code behind. I am reading about Attached Properties, but cannot see how they are to be applied here.</p></li> </ul> <p>(Please note: I am using the common 'RelayCommand' elsewhere in the application; does this come into play here??)</p> <p><strong>THIRD PROBLEM</strong>: When I do use the non-MVVM way of firing the command in the code behind event handler, you can see that I am passing in the Selected Customer Id as an arguement into the command. How do I see that argument in the Command handler in viewCustomer? I create a new RelayCommand to handle it, but it seems the Execute method does not take arguments?</p> <p>Given all of the above, I have to say that I do NOT personally subscribe to the 'MVVM means NO CODE IN THE VIEW'. That seems crazy to me; code that is entirely to do with the view, and the view only, should not - IMHO - go in the viewmodel. That said, though, this does seem like logic-y stuff (not view stuff).</p> <p>Many thanks for some insight. Sorry for the long post; trying to balance enough information for you to help me with 'War and Peace'.</p> <p>DS</p>
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