TreeView.ExpandAll Method

The ExpandAll method expands all the TreeNode objects, including all the child tree nodes, that are in the TreeView control.

Note:
The state of a TreeNode persists. For example, suppose that you call the ExpandAll method, and then the individual root tree nodes are collapsed. The child tree nodes have not been collapsed, and will appear in their previously-expanded state when the root tree nodes are expanded again. Calling the CollapseAll method ensures that all the tree nodes appear in the collapsed state.

The following code example expands all the tree nodes in a TreeView control when a CheckBox is checked, and collapses the FirstNode when the CheckBox is cleared. This example requires that you have a Form with a CheckBox, and a TreeView control with a TreeNodeCollection that has several TreeNode objects (preferably with three or more levels).

private void myCheckBox_CheckedChanged(object sender, System.EventArgs e)
{
   // If the check box is checked, expand all the tree nodes. 
   if (myCheckBox.Checked == true)
   {
      myTreeView.ExpandAll();
   }
   else
   {
      // If the check box is not cheked, collapse the first tree node.
      myTreeView.Nodes[0].FirstNode.Collapse();
      MessageBox.Show("The first and last  node of CutomerList root node is collapsed");
   }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

.NET Compact Framework

Reference