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Tri-State TreeView Control

, 2 Nov 2005 CPL
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A TreeView control with tri-state checkboxes.


Microsoft provides a TreeView control in the .NET framework, but as usual it doesn't expose all the functionality that the underlying common control provides. It has the possibility to display check-boxes but they can't be tri-state check boxes.

This control adds tri-state check boxes and the necessary handling methods to check/uncheck all sub-items if the user clicks on a node, as well as displays a grey-checked check box for the parent if the siblings have differing check/uncheck states.


A tri-state TreeView is a tree view control that displays check boxes next to the tree nodes. If you click on a check box, it checks (or unchecks) the check box and all sub-nodes.

If the nodes on the same level as the clicked node have differing check states the parent node's check box is grey-checked as well as its parent's and so on.

If you click on a grey-checked check box it unchecks that node and all its subnodes.

How to use the control

Add TriStateTreeView.cs to your project and then simply drop the TriStateTreeView control on a form and use it as a regular TreeView control. The only difference is when you want to access the checked state of a node. Instead of using the treeNode.Checked property you call triStateTreeView.GetChecked(treeNode) resp. triStateTreeView.SetChecked(treeNode, checkState). Instead of a bool these methods take a CheckState.

For example, the following code snippet checks the state of all the top level nodes:

foreach (TreeNode node in m_treeView.Nodes)
  if (m_treeView.GetChecked(node) == 

How does it work?

The control derives from TreeView and sets the ImageList and SelectedImageList properties for the base control. It overrides the OnClick and OnKeyDown methods.

In the OnKeyDown method, we check if the pressed key is a space, and if it is we change the state of the selected node.

The OnClick method is a little trickier. We have to use the TVM_HITTEST Win32 API message to determine if the user clicked on the icon or on the item. If the user clicked on the icon we change the state of the selected node.


This control doesn't support displaying both check boxes and icons. If you need this functionality you have to call additional Win32 API methods. The common control tree view control supports having multiple image lists, but this functionality isn't exposed in .NET.


The control makes use of the Skybound.VisualStyle assembly from By commenting out the lines that reference that assembly it will easily work without it. Another way of making the control aware of visual styles is described here.

The demo project consists of an assembly that contains the TriStateTreeView, a demo project and a NUnit test assembly with some tests for the control.


  • 26 March 2004 - First version.
  • 28 October 2005 - Added support for visual styles and Before/AfterCheck.


This article, along with any associated source code and files, is licensed under The Common Public License Version 1.0 (CPL)


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Comments and Discussions

Generalcheck box can't be displayed Pinmemberjustanumber29-Jul-07 7:21 
GeneralRe: check box can't be displayed PinmemberCodeForFun20-Sep-07 8:49 
GeneralRe: check box can't be displayed Pinmemberzz_lsl20-Dec-10 4:40 
GeneralOnBeforeCheck [modified] Pinmembermjelten19-Jul-07 23:23 
QuestionReset all to unchecked? PinmemberJim Baldwin24-Jun-07 20:30 
QuestionHow to add multiple images on same tree node? Pinmembersushantya6-Mar-07 20:39 
GeneralTri-State TreeView in Pocket Project PinmemberSilas Pereira27-Feb-07 2:08 
QuestionHow do I get what is checked? PinmemberJoppeG26-Feb-07 22:33 
Im making a Database access program and like this tri-state method for sorting the tables. Im getting this to sort the tables as thay should, how ever. When I try to call what boxes are checked there is no output. from the ArrayList.
Right now I have a peace of code that is run when Connect/Refresh button is pushed.
It looks like this.

public void scThreeCheckedChoises()
ArrayList ChkList = new ArrayList();
ChkList = dcTriStateTreeView2.GetCheckedTagData();
string test = System.String.Concat(ChkList.ToArray());
string ChkStr = "";
foreach (string s in ChkList)
ChkStr = s;

I want it to a singel string row as it should talk to the SQL server what tables to select.
I get nothing out at all, shouldnt I use .GetCheckedData to retrive the checked alternativs in treeview? Would be grate If anyone could help.
AnswerArrayList Bug? PinmemberJoppeG28-Feb-07 1:55 
GeneralSolved problem PinmemberJoppeG28-Feb-07 5:07 
GeneralRe: Solved problem Pinmemberjonmach18-Nov-07 8:38 
QuestionRight-To-Left Problem Pinmembermorali2k2-Sep-06 3:58 
GeneralSimplified tree-state TreeView PinmemberLaurent Muller22-Aug-06 5:35 
GeneralRe: Simplified tree-state TreeView PinmemberUncleRedz1-Nov-06 5:18 
GeneralRe: Simplified tree-state TreeView Pinmemberbarclay19-Dec-06 12:44 
GeneralRe: Simplified tree-state TreeView Pinmemberhamlet_13-Feb-07 1:38 
GeneralRe: Simplified tree-state TreeView PinmemberMartin Welker4-Jun-07 13:17 
GeneralRe: Simplified tree-state TreeView Pinmembercwalex24-Jul-07 12:26 
GeneralRe: Simplified tree-state TreeView PinmemberMAEI28-Sep-07 9:25 
GeneralRe: Simplified tree-state TreeView PinmemberLaurent Muller1-Oct-07 5:08 
GeneralRe: Simplified tree-state TreeView (do not set Checkboxes to True) PinmemberDial@Technet30-Oct-07 5:30 
GeneralRe: Simplified tree-state TreeView Pinmemberjcachat16-Nov-07 7:55 
GeneralRe: Simplified tree-state TreeView Pinmemberluisxvarg12-Jan-10 0:38 
GeneralSuggestion about using StateImageList Pinmemberlukasz_sw21-Feb-06 13:06 
GeneralImplementing an icon Pinmemberdevnet24730-Jan-06 20:54 

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