Thanks to Microsoft Support, the mystery is solved.

If the Form containing the TreeView is instantiated in the add-in startup function as below, the icons appear!

public partial class ThisApplication
{
Form1 frm;

private void ThisApplication_Startup(object sender, System.EventArgs e)
{
frm = new Form1();
frm.Show();

}

BUT, if instantiated with the class, as below:

public partial class ThisApplication
{
Form1 frm = new Form1();

private void ThisApplication_Startup(object sender, System.EventArgs e)
{
frm.Show();

}

Then they do NOT appear. Furthermore, if "VisualStyles" (new with XP) are disabled, the icons work in both instances.

-Allen

Thanks to Microsoft Support, the mystery is solved.

If the Form containing the TreeView is instantiated in the add-in startup function as below, the icons appear!

public partial class ThisApplication
{
Form1 frm;

private void ThisApplication_Startup(object sender, System.EventArgs e)
{
frm = new Form1();
frm.Show();

}

BUT, if instantiated with the class, as below:

public partial class ThisApplication
{
Form1 frm = new Form1();

private void ThisApplication_Startup(object sender, System.EventArgs e)
{
frm.Show();

}

Then they do NOT appear. Furthermore, if "VisualStyles" (new with XP) are disabled, the icons work in both instances.

-Allen

Ohhh!!

The example code I found everywhere didn't fit my problem.

but these words helpd so I called Application.EnableVisualStyles(). BEFORE creating the form containing the treeview


Application.EnableVisualStyles(); // << Must come first
theAuxTreeForm = new FormTreeMap; // Form that contains the treeview
////Application.EnableVisualStyles(); // << no icons images in the tree if only enabled here
theMainForm= new FormMain;
Application.Run(theMainForm);