#Wpf treeview template example update#

((INotif圜ollectionChanged) AssociatedObject.Items).CollectionChanged += OnTreeViewItemsChanged ĪssociatedObject.ItemContainerStyle?.Setters?.Remove(_treeViewItemEventSetter) ĪssociatedObject.SelectedItemChanged -= OnTreeViewSelectedItemChanged UpdateTreeViewItem((TreeViewItem) sender, false) ĪssociatedObject.SelectedItemChanged += OnTreeViewSelectedItemChanged Private void OnTreeViewItemLoaded(object sender, RoutedEventArgs args) Private void OnTreeViewSelectedItemChanged(object sender, RoutedPropert圜hangedEventArgs args) Private void OnTreeViewItemsChanged(object sender, Notif圜ollectionChangedEventArgs args) If (!(_treeViewItemEventSetter))Ī(_treeViewItemEventSetter) Var style = new Style(typeof(TreeViewItem),Ī(typeof(TreeViewItem)) as Style) ĪssociatedObject.ItemContainerStyle = style If (AssociatedObject.ItemContainerStyle = null) Inject Loaded event handler into ItemContainerStyle Recurse into children in case some of them are already loaded If HierarchyPredicate is not set, this will always be trueīool isParentOfModel = HierarchyPredicate?.Invoke(SelectedItem, model) ? true If we find the item's parent instead - expand it If (SelectedItem = model & !item.IsSelected) If we find the item we're looking for - select it Private void UpdateTreeViewItem(TreeViewItem item, bool recurse)

#Wpf treeview template example update#

Update state of all items starting with given, with optional recursion New RoutedEventHandler(OnTreeViewItemLoaded) _treeViewItemEventSetter = new EventSetter( Set => SetValue(ExpandSelectedProperty, value) Get => (bool) GetValue(ExpandSelectedProperty) Set => SetValue(HierarchyPredicateProperty, value) Get => (IsChildOfPredicate) GetValue(HierarchyPredicateProperty) Public IsChildOfPredicate HierarchyPredicate Predicate that checks if two items are hierarchically related Set => SetValue(SelectedItemProperty, value) Private readonly EventSetter _treeViewItemEventSetter Var behavior = (TreeViewSelectionBehavior) sender Private static void OnSelectedItemChanged(DependencyObject sender, DependencyPropert圜hangedEventArgs args)

Public static readonly DependencyProperty ExpandSelectedProperty = Public static readonly DependencyProperty HierarchyPredicateProperty = Public static readonly DependencyProperty SelectedItemProperty =įrameworkPropertyMetadataOptions.BindsTwoWayByDefault, Public delegate bool IsChildOfPredicate(object nodeA, object nodeB) Here's the behavior I've implemented: public class TreeViewSelectionBehavior : Behavior When one of the nodes we expanded is loaded, it triggers an event, and we start again from the top.If we instead find its parent, expand it so that we can continue the search once it's loaded.If we manage to find it, select it and exit early.When SelectedItem changes, go through all loaded tree nodes and try to locate the target node.Subscribe to the Loaded event of all data items using a style.We can, however, subscribe to the Loaded event of each data item, which will trigger once the control has been loaded.

I naively assumed that by expanding the node from code, its children's item containers will immediately become available, but this is not the case because that's handled asynchronously. In order to make our target node visible, we need to expand all of its ancestor nodes one by one, starting from the very top. However, if the node is not visible yet, then the container is also not initialized, making the method return null. This in itself can be accomplished by using the (.) method. To access the IsSelected and IsExpanded properties I needed to resolve a reference to an instance of TreeViewItem, which is a container that wraps around the data template. I realized that to solve this I would have to traverse the entire hierarchy of tree nodes, but that wasn't the only problem. I solved this problem by writing a small behavior that takes care of this for me. This was a deal-breaker for me because I wanted the tree view to navigate to the newly selected item, even if it wasn't immediately visible. Both of these approaches suffer from the same problem - an item won't get selected if its parents are not yet expanded. I googled the problem and every resource I've found was guiding me into either handling it in code-behind or adding an IsSelected property to my model class. I think there's no point explaining why binding SelectedItem would be useful, so there should be no surprise in my disappointment. Recently I realized that TreeView.SelectedItem property is read-only and unbindable. The longer I work with WPF, the more I notice how many things it's missing.