Deborah's Developer MindScape

This post describes how to populate a WinForms TreeView control from an XML file assuming you are targeting the .NET Framework Version 3.5.

The XML file used in this example looks like this:

<States>
  <State name="California">
    <Regions>
      <Region name="San Luis Obispo">
        <Area name="Santa Maria" />
        <Area name="Seaside" />
      </Region>
      <Region name="Silicon Valley">
        <Area name="San Jose"/>
        <Area name="Sunnyvale"/>
      </Region>
    </Regions>
  </State>
  <State name="Wisconsin">
    <Regions>
      <Region name="Milwaukee">
        <Area name ="Mukwanago"/>
        <Area name="Germantown"/>
      </Region>
      <Region name="Fox Valley">
        <Area name="Oshkosh" />
        <Area name="Appleton" />
      </Region>    
    </Regions>
  </State>
</States>

The TreeView will display the following:

State
— Region
—— Area

The code is provided here in VB and C# and then described in detail below.

NOTE: Be sure to set a reference to System.Core and System.Xml.Linq

In C#:

XElement doc  = XElement.Load("testXML.xml");

TreeNode stateNode;
TreeNode regionNode;
foreach (XElement state  in doc.Descendants("State"))
{
    stateNode = treeView1.Nodes.Add(state.Attribute("name").Value);
    foreach (XElement region in state.Descendants("Region"))
    {
        regionNode =
            stateNode.Nodes.Add(region.Attribute("name").Value);
        foreach (XElement area in region.Descendants("Area"))
        {
            regionNode.Nodes.Add(area.Attribute("name").Value);
        }
    }
}

In VB:

Dim doc As XElement = XElement.Load("testXML.xml")

Dim stateNode As TreeNode
Dim regionNode As TreeNode
For Each state As XElement In doc…<State>
    stateNode = TreeView1.Nodes.Add(state.@name)
    For Each region As XElement In state…<Region>
        regionNode = stateNode.Nodes.Add(region.@name)
        For Each area As XElement In region…<Area>
            regionNode.Nodes.Add(area.@name)
        Next
    Next
Next

In both cases, the XML is first retrieved from a file. An in-memory XML string could be used instead.

Three for/each loops are used, one for each level of the TreeView hierarchy.

The states are processed first. A node is added for each state name.

The regions are processed next. A node is added under the state for each region name.

Finally, the areas are processed. A node is added under the region for each area name.

Notice that the VB code leverages XML literals. The C# code uses XElements (which also work in VB).

Enjoy!