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POAuto cancel changes in DataForm when selection is changed
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  1. POAuto cancel changes in DataForm when selection is changed
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    copied!<p>I wonder how you do such thing. Assume, we have MVVM CRUD app which modifies a tree (menu structure, for example). We have a view model with the menu items and two views: the first with a <code>TreeView</code> and the second with a <code>DataForm</code>. Main problems are:</p> <ol> <li><code>DataForm</code> can not handle hierarchical data.</li> <li>Depending on the menu item selected in the <code>TreeView</code> the <code>DataForm</code> should display different set of fields (for example for menu items with children or without).</li> </ol> <p>I've ended up with the following. View model has 3 fields:</p> <ol> <li><code>Items</code> — the collection of <code>MenuItem</code> objects which have their own <code>Children</code> collection for building hierarchical data source.</li> <li><code>SelectedItem</code> — currently selected <code>MenuItem</code> in the <code>TreeView</code>.</li> <li><code>EditedItem</code> — <code>EditViewModel</code> object which basically has two descendants: <code>MenuItemEditViewModel</code> and <code>LeafMenuItemEditViewModel</code>. This property is set automatically when <code>SelectedItem</code> is changed. Its actual type is inferred from the <code>SelectedItem.Children</code> emptiness.</li> </ol> <p><code>TreeView</code> is bound to <code>Items</code> and <code>SelectedItem</code>. <code>DataForm</code> is not required to maintain currency in this case (instead current item is set by the <code>TreeView</code>) nor it is responsible for creating and deleting items. That's why I decided to bind only its <code>CurrentItem</code> to view model's <code>EditedItem</code> (<code>ItemsSource</code> is unbound). Its <code>AutoCommit</code> is set to <code>False</code> (when it is <code>True</code> and <code>ItemsSource</code> is unbound all current item changes get copied to newly selected item when you select different item in the <code>TreeView</code>, which is not so nice). <code>DataForm</code> fields are autogenerated.</p> <p>Obviously, that now if we select an item in the <code>TreeView</code>, then make some changes in the <code>DataForm</code> and try to select different item in the <code>TreeView</code> we'll get well-known</p> <blockquote> <p>Cannot change currency when an item has validation errors or it is being edited and AutoCommit is false. Set ItemsSource to a ICollectionView to manage currency instead</p> </blockquote> <p>In this case I want <code>DataForm</code> to discard all changes implicitly. There is a workaround to call <code>DataForm.CancelEdit()</code> before <code>TreeView</code> selected item is changed (usually an event like <code>PreviewSelectionChanged</code> or <code>BeforeSelectionChanged</code>). But it is not the MVVM way since the <code>TreeView</code> and the <code>DataForm</code> are defined in completely different views (read: is not acceptable).</p> <p>Is there something like AutoCancel which forces <code>DataForm</code> to cancel changes when its <code>CurrentItem</code> is changed? Maybe someone from dev team can answer? Or how would you deal with such problem?</p>
 

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