Question

I would like to know how to bind a custom data type to a TreeView.

The data type is basically an arraylist of objects that contain other arraylists. Access would look something like this:

foreach (DeviceGroup dg in system.deviceGroups)
    {
        foreach (DeviceType dt in dg.deviceTypes)
        {
            foreach (DeviceInstance di in dt.deviceInstances)
            {

            }
        }
    }

I would like the TreeView to look something like this:

DeviceGroup1

 --> DeviceType1
      --DeviceInstance1
      --DeviceInstance2
 --> DeviceType2
      --DeviceInstance1

DeviceGroup2

 --> DeviceType1
      --DeviceInstance1
 --> DeviceType2

Answer 1

Ok this is where the HierarchicalDataTemplate will save you. The trick is you will need to use two different hierarchical templates, since you have a three-level hierarchy here. I have constructed a simple UserControl to illustrate. First, here is some code-behind creating model data similar to what you have:

public partial class ThreeLevelTreeView : UserControl
{
    public ArrayList DeviceGroups { get; private set; }

    public ThreeLevelTreeView()
    {
        DeviceInstance inst1 = new DeviceInstance() { Name = "Instance1" };
        DeviceInstance inst2 = new DeviceInstance() { Name = "Instance2" };
        DeviceInstance inst3 = new DeviceInstance() { Name = "Instance3" };
        DeviceInstance inst4 = new DeviceInstance() { Name = "Instance4" };

        DeviceType type1 = new DeviceType() { Name = "Type1", DeviceInstances = new ArrayList() { inst1, inst2 } };
        DeviceType type2 = new DeviceType() { Name = "Type2", DeviceInstances = new ArrayList() { inst3 } };
        DeviceType type3 = new DeviceType() { Name = "Type3", DeviceInstances = new ArrayList() { inst4 } };
        DeviceType type4 = new DeviceType() { Name = "Type4" };

        DeviceGroup group1 = new DeviceGroup() { Name = "Group1", DeviceTypes = new ArrayList() { type1, type2 } };
        DeviceGroup group2 = new DeviceGroup() { Name = "Group2", DeviceTypes = new ArrayList() { type3, type4 } };

        DeviceGroups = new ArrayList() { group1, group2 };

        InitializeComponent();
    }
}

public class DeviceGroup
{
    public string Name { get; set; }
    public ArrayList DeviceTypes { get; set; }
}

public class DeviceType
{
    public string Name { get; set; }
    public ArrayList DeviceInstances { get; set; }
}

public class DeviceInstance
{
    public string Name { get; set; }
}

Nothing difficult here, but note that you should use ObservableCollection instead of ArrayList if you want to add and remove from your collections dynamically. Now let’s look at the XAML for this control:

<UserControl x:Class="TestWpfApplication.ThreeLevelTreeView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TestWpfApplication"
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<TreeView ItemsSource="{Binding DeviceGroups}">
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate ItemsSource="{Binding DeviceTypes}">
            <HierarchicalDataTemplate.ItemTemplate>
                <HierarchicalDataTemplate ItemsSource="{Binding DeviceInstances}">
                    <TextBlock Text="{Binding Name}"/>
                </HierarchicalDataTemplate>
            </HierarchicalDataTemplate.ItemTemplate>
            <TextBlock Text="{Binding Name}"/>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

And here is the result:

alt text http://img684.imageshack.us/img684/6281/threeleveltreeview.png