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POWPF TreeView Dynamic Grouping
 

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    <p>I'm attempting to create a TreeView in WPF that is bound to a CollectionViewSource. I create groups in the CollectionViewSource and have the HierarchicalDataTemplate setup in the XAML to display the TreeView properly.</p> <p>In my ViewModel I have a method to change the Grouping of the CollectionViewSource and all seems to work well. The only issue I have is displaying the CollectionViewSource without any grouping.</p> <p>Does anyone know how to design the template to accommodate a scenario where the CollectionViewSource has no groupings, but can also accommodate a CollectionViewSource with groupings?</p> <p><strong>Update</strong> I have created some sample code to better describe what I'm doing. The DataTemplateSelector works when the app starts but I can't figure out how to re-fire the DataTemplate Selector when the user selects a different grouping option from the combobox. Below is my sample code</p> <pre><code>&lt;Window x:Class="TreeViewGroupTest.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:TreeViewGroupTest" Title="WindowsApplication1" Height="Auto" Width="300"&gt; &lt;Window.Resources&gt; &lt;local:SchoolTemplateSelector x:Key="schoolTemplateSelector" /&gt; &lt;HierarchicalDataTemplate x:Key="BasicList" ItemsSource="{Binding TeachersBy.Source}"&gt; &lt;StackPanel&gt; &lt;TextBlock Text="{Binding Name}" /&gt; &lt;ComboBox SelectionChanged="ComboBox_SelectionChanged" ItemsSource="{Binding GroupByList}" /&gt; &lt;/StackPanel&gt; &lt;HierarchicalDataTemplate.ItemTemplate&gt; &lt;DataTemplate&gt; &lt;TextBlock Text="{Binding Last}" /&gt; &lt;/DataTemplate&gt; &lt;/HierarchicalDataTemplate.ItemTemplate&gt; &lt;/HierarchicalDataTemplate&gt; &lt;HierarchicalDataTemplate x:Key="GroupList" ItemsSource="{Binding TeachersBy.View.Groups}"&gt; &lt;StackPanel&gt; &lt;TextBlock Text="{Binding Name}" /&gt; &lt;ComboBox SelectionChanged="ComboBox_SelectionChanged" ItemsSource="{Binding GroupByList}" /&gt; &lt;/StackPanel&gt; &lt;HierarchicalDataTemplate.ItemTemplate&gt; &lt;HierarchicalDataTemplate ItemsSource="{Binding Items}"&gt; &lt;TextBlock Text="{Binding Name}" /&gt; &lt;HierarchicalDataTemplate.ItemTemplate&gt; &lt;DataTemplate&gt; &lt;TextBlock Text="{Binding Last}" /&gt; &lt;/DataTemplate&gt; &lt;/HierarchicalDataTemplate.ItemTemplate&gt; &lt;/HierarchicalDataTemplate&gt; &lt;/HierarchicalDataTemplate.ItemTemplate&gt; &lt;/HierarchicalDataTemplate&gt; &lt;/Window.Resources&gt; &lt;StackPanel&gt; &lt;TreeView ItemsSource="{Binding Schools}" ItemTemplateSelector="{Binding schoolTemplateSelector}" /&gt; &lt;/StackPanel&gt; </code></pre> <p></p> <p>and the code behind</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows; using System.Windows.Controls; using System.Windows.Data; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Imaging; using System.Windows.Navigation; using System.Windows.Shapes; using System.Collections.ObjectModel; namespace TreeViewGroupTest { /// &lt;summary&gt; /// Interaction logic for MainWindow.xaml /// &lt;/summary&gt; public partial class MainWindow : Window { public ObservableCollection&lt;School&gt; Schools { get; set; } public SchoolTemplateSelector schoolTemplateSelector { get; set; } private string group = "Subject"; public string GroupByChoice { get; set; } public MainWindow() { InitializeComponent(); GroupByChoice = "Subject"; Schools = new ObservableCollection&lt;School&gt; { new School { Name = "Apple", Teachers = new ObservableCollection&lt;Teacher&gt; { new Teacher { Last = "Alpha", Subject = "Math" , Grade = "9th" }, new Teacher { Last = "Beta", Subject = "English" , Grade = "9th" }, new Teacher { Last = "Charlie", Subject = "Math" , Grade = "9th" }, new Teacher { Last = "Delta", Subject = "English" , Grade = "10th" }, new Teacher { Last = "Echo", Subject = "Math" , Grade = "10th" }, new Teacher { Last = "Foxtrot", Subject = "English" , Grade = "10th" }, } }, new School { Name = "Microsoft", Teachers = new ObservableCollection&lt;Teacher&gt; { new Teacher { Last = "Alpha", Subject = "Math" , Grade = "9th" }, new Teacher { Last = "Beta", Subject = "English" , Grade = "9th" }, new Teacher { Last = "Charlie", Subject = "Math" , Grade = "9th" }, new Teacher { Last = "Delta", Subject = "English" , Grade = "10th" }, new Teacher { Last = "Echo", Subject = "Math" , Grade = "10th" }, new Teacher { Last = "Foxtrot", Subject = "English" , Grade = "10th" }, } }, }; Schools[0].SetTeacher(); ; Schools[1].GroupBy("Subject"); Schools[1].TeachersBy.View.Refresh(); this.DataContext = this; schoolTemplateSelector = new SchoolTemplateSelector(); } private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e) { string prop = e.AddedItems[0].ToString(); if (prop != "None") { foreach (School s in Schools) { s.GroupBy(prop); } } else { foreach (School s in Schools) { s.TeachersBy.GroupDescriptions.Clear(); } } //The DataTemplateSelector should fire now... } } public class School { public string Name { get; set; } public ObservableCollection&lt;Teacher&gt; Teachers { get; set; } public CollectionViewSource TeachersBy { get; set; } public ObservableCollection&lt;String&gt; GroupByList { get; set; } public School() { Teachers = new ObservableCollection&lt;Teacher&gt;(); TeachersBy = new CollectionViewSource(); GroupByList = new ObservableCollection&lt;string&gt; { "None", "Subject", "Grade" }; } public void SetTeacher() { TeachersBy.Source = Teachers; } public void GroupBy(string propertyName) { TeachersBy.Source = Teachers; TeachersBy.GroupDescriptions.Clear(); TeachersBy.GroupDescriptions.Add(new PropertyGroupDescription(propertyName)); TeachersBy.View.Refresh(); } } public class Teacher { public string Last { get; set; } public string Subject { get; set; } public string Grade { get; set; } public Teacher() { } } public class SchoolTemplateSelector : DataTemplateSelector { public override DataTemplate SelectTemplate(object item, DependencyObject container) { FrameworkElement element = container as FrameworkElement; if (item is School &amp;&amp; (item as School).TeachersBy.GroupDescriptions.Count &gt; 0) { return element.FindResource("GroupList") as DataTemplate; } else { return element.FindResource("BasicList") as DataTemplate; } } } } </code></pre>
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