how can i display hierarchical data in a list box using data templates in wpf

Question

I have a hierarchical collection of Groups and SubGroups like:

• Group 1
  • SubGroup1
  • SubGroup2
• Group 2
  • SubGroup1

What i want to do is to display this hierarchical data in a list box. i tried to create different data templates and i am able to show the SubGroups but am not able to display the Group Names.

The class that i use for this purpose is something like this:

public class Groups
{
public string Group {get; set;}
public List<string> SubGroup {get; set;}
}

I bind a List to ItemsSource of the listbox. What i need is a data template that i can use to display this data hierarchically.

i cannot use another control for this, i have to use a listbox.

Edit: By looking at the suggestion provided by Desty, i am able to display the values using this Data Template

<DataTemplate x:Key="SubGroups">
  <StackPanel>
    <Label Content="{Binding Path=Group}" />
    <ItemsControl Margin="30,0,0,0" ItemsSource="{Binding SubGroup}" />
  </StackPanel>
</DataTemplate>

The problem now is that i am unable to select individual sub groups from the list box. It selects the complete ListBoxItem and i am not able select individual sub groups.

Answer 1

What you need is a second class for SubGroups, so you can define one DataTemplate for Groups and one for SubGroups. Your model classes could be something like

public class Group {
  public string Name { get; set; }
  public List<SubGroup> SubGroups { get; set; }
  public Group(string name) { this.Name = name; }
}

public class SubGroup {
  public string Name { get; set; }
  public SubGroup(string name) { this.Name = name; }
}

In WPF you can define a DataTemplate for each type:

<Window.Resources>
  <DataTemplate DataType="{x:Type local:SubGroup}">
    <StackPanel Orientation="Horizontal">
      <TextBlock Text=" +-- "/><TextBlock Text="{Binding Name}"/>
    </StackPanel>
  </DataTemplate>
  <DataTemplate DataType="{x:Type local:Group}">
    <StackPanel>
      <TextBlock Text="{Binding Name}"/>
      <ItemsControl ItemsSource="{Binding SubGroups}"/>
     </StackPanel>
  </DataTemplate>
</Window.Resources>
<Grid>
  <ListBox ItemsSource="{Binding}" />
</Grid>

Edit (after reviewing Bhattis edit):

If sub group items shall also be clickable, then (IMHO) there cannot be a difference between a group and a subgroup from the ListBox's point of view. So my workaround guess is:

public class Groups {
  public string Group { get; set; }
} 

In the WPF window

<ListBox ItemsSource="{Binding}">
  <ListBox.ItemTemplate>
    <DataTemplate>
      <StackPanel>
        <Label Content="{Binding Path=Group}" />
      </StackPanel>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>

And in the WPF code behind file:

public MainWindow() {
  InitializeComponent();
  Groups g1 = new Groups() { Group = "Parent 1" };
  Groups s1 = new Groups() { Group = "   Sub 1" };
  Groups s2 = new Groups() { Group = "   Sub 2" };
  Groups g2 = new Groups() { Group = "Parent 2" };
  Groups s3 = new Groups() { Group = "   Sub 1" };
  Groups s4 = new Groups() { Group = "   Sub 2" };
  this.DataContext = new List<Groups>() { g1, s1, s2, g2, s3, s4 };
}

Here every subgroup is nothing else than a group, so every "line" is clickable. Important is that the sequence of the list matters a lot, because the structure is no longer in the model.

If you must react differently depending on wether the user clicked a group or a subgroup, then you can build a inheritance hierarchy in your model and put the corresponding objects in the DataContext. To bring you in the right direction, I mean something like

public abstract class AbstractGroup {
    public string Name { get; set; }
    public AbstractGroup(string name) { this.Name = name; }
}
public class Group : AbstractGroup {
    public Group(string name) : base(name) {}
}
public class SubGroup : AbstractGroup {
    public SubGroup(string name) : base(name) {}
} 

Code-behind:

    InitializeComponent();
    AbstractGroup g1 = new Group("Parent 1");
    AbstractGroup s1 = new SubGroup("  Sub 1");
    AbstractGroup s2 = new SubGroup("   Sub 2");
    AbstractGroup g2 = new Group("Parent 2");
    AbstractGroup s3 = new SubGroup("   Sub 1");
    AbstractGroup s4 = new SubGroup("   Sub 2");
    this.DataContext = new List<AbstractGroup>() { g1, s1, s2, g2, s3, s4 };

XAML:

<ListBox ItemsSource="{Binding}">
  <ListBox.ItemTemplate>
    <DataTemplate>
      <StackPanel>
        <Label Content="{Binding Path=Name}" />
      </StackPanel>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>

Since you can get the selected object in the DataContext, typeof() helps you finding out which concrete type the selected item is.