Using expander in treeview

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Basically I need something with expander control.
I have a main expander. Under it it has many sections. What I want is to put the sections in a treeview. Each section also has its own expander. The main expander controls all. Which means if it collapses, all sections should be collapsed, vice versa.

The changeling part is that I want to set the background. I want the background of the expanders are different. When sections expand, the background of the sections are different from the main expander.

What I have tried:

I tried to use template to customize the expanders, but not sure how to trigger the background with the styles. I can't find the similar example online. Need help.

Posted 25-Nov-17 2:34am

Member 12658724

Updated 22-Mar-18 2:19am

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Graeme_Grant 25-Nov-17 8:43am

Have you looked at the TreeView template? They're already expanders, you only need to style them. You can see the template here: TreeView Styles and Templates | Microsoft Docs[^]

Member 12658724 25-Nov-17 10:18am

Did you mean I have to style the ToggleButton? When I click it the style will be changed by some trigger?

Graeme_Grant 25-Nov-17 11:06am

You have total control over the look and feel to achieve what you want. I do just that in the WpfFileExplorer sample in this article: Working with JSON in C# & VB[^]

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Clifford Nelson · Answer 1 · 2018-03-22T02:20:00

You can use the VisualTreeHelper:

private static IEnumerable<T> FindVisualChildren<T>(DependencyObject root) where T : DependencyObject
 {
     if (root != null)
         for (int i = 0; i < VisualTreeHelper.GetChildrenCount(root); i++)
         {
             DependencyObject child = VisualTreeHelper.GetChild(root, i);
             if (child is T) yield return (T)child;
             foreach (T childOfChild in FindVisualChildren<T>(child))
                 yield return childOfChild;
         }
 }

use the following

var treeItems = FindVisualChildren<treeviewitem> (this),ToList();
treeItems.ForEach(I => i.IsExpanded = false);