Simple Tri-State TreeView

Introduction

I had too many problems with the original code and decided to rewrite most of it.

Using the Code

"Refreshing" the treeview after a change is not needed any longer (but still works). The checkbox of a newly added node will appear automatically if you set its state with the function "SetState". Alternatively, you can display the checkboxes in their initial state with the functions "InitializeCBImages" (for all nodes) or "InitializeStates" (for a specific node collection).

BeforeCheck and AfterCheck are now triggered only for the node modified by the SetState function or a mouse click. Other changes (to parents and children state) trigger a new event: AutoCheck.

Here's the new code for the class:

public class TriStateCBTreeView : TreeView {

    // ~~~ fields ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    ImageList _ilStateImages;
    bool _bUseTriState;
    bool _bCheckBoxesVisible;
    bool _bPreventCheckEvent;

    // ~~~ constructor ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    /// <summary>
    /// Creates a new instance
    /// of this control.
    /// </summary>
    public TriStateCBTreeView()
        : base() {
        _ilStateImages = new ImageList();                            // first we create 
                                                                     // our state image
        CheckBoxState cbsState = CheckBoxState.UncheckedNormal;      // list and pre-init 
                                                                     // check state.

        for (int i = 0; i <= 2; i++) {                               // let's iterate each tri-state
            Bitmap bmpCheckBox = new Bitmap(16, 16);                 // creating a new 
                                                                     // checkbox bitmap
            Graphics gfxCheckBox = Graphics.FromImage(bmpCheckBox);  // and getting 
                                                                     // graphics object from
            switch (i)                                               // it...
            {
                case 0: cbsState = CheckBoxState.UncheckedNormal; break;
                case 1: cbsState = CheckBoxState.CheckedNormal; break;
                case 2: cbsState = CheckBoxState.MixedNormal; break;
            }
            CheckBoxRenderer.DrawCheckBox(gfxCheckBox, new Point(2, 2), cbsState);  // ...rendering
            gfxCheckBox.Save();                                         // the checkbox and
            _ilStateImages.Images.Add(bmpCheckBox);                     // adding to state image list.
        }

        _bUseTriState = true;
    }

    // ~~~ properties ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    /// <summary>
    /// Gets or sets to display
    /// checkboxes in the tree
    /// view.
    /// </summary>
    [Category("Appearance")]
    [Description("Sets tree view to display checkboxes or not.")]
    [DefaultValue(false)]
    public new bool CheckBoxes {
        get { return _bCheckBoxesVisible; }
        set {
            _bCheckBoxesVisible = value;
            base.CheckBoxes = _bCheckBoxesVisible;
            this.StateImageList = _bCheckBoxesVisible ? _ilStateImages : null;
        }
    }

    [Browsable(false)]
    public new ImageList StateImageList {
        get { return base.StateImageList; }
        set { base.StateImageList = value; }
    }

    /// <summary>
    /// Gets or sets to support
    /// tri-state in the checkboxes
    /// or not.
    /// </summary>
    [Category("Appearance")]
    [Description("Sets tree view to use tri-state checkboxes or not.")]
    [DefaultValue(true)]
    public bool CheckBoxesTriState {
        get { return _bUseTriState; }
        set { _bUseTriState = value; }
    }

    // ~~~ functions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    /// <summary>
    /// Changes nodes state.
    /// </summary>

    protected void SetParentState(TreeNode tNode) {
        TreeNode ParentNode = tNode.Parent;
        if (ParentNode != null) {
            try {
                if (tNode.StateImageIndex == 2) {                   // if the current node has 
                                                                    // a mixed state
                    ParentNode.Checked = false;                     // then its parent is set to 
                                                                    // the same state
                    ParentNode.StateImageIndex = 2;
                    return;
                }
                int CheckedCount = 0;
                int UnCheckedCount = 0;
                foreach (TreeNode ChildNode in ParentNode.Nodes) {  // we count the checked 
                                                                    // and unchecked states
                    if (ChildNode.StateImageIndex <= 0)             // of each node at 
                                                                    // the current level
                        UnCheckedCount++;
                    else if (ChildNode.StateImageIndex == 1)
                        CheckedCount++;
                    if (ChildNode.StateImageIndex == 2 ||           // if one node has a 
                                                                    // mixed state or there
                       (CheckedCount > 0 && UnCheckedCount > 0)) {  // are checked and 
                                                                    // unchecked states, then
                        ParentNode.Checked = false;                 // the parent node is set to 
                                                                    // a mixed state
                        ParentNode.StateImageIndex = 2;
                        return;
                    }
                }
                if (UnCheckedCount > 0) {
                    ParentNode.Checked = false;
                    ParentNode.StateImageIndex = 0;
                }
                else if (CheckedCount > 0) {
                    ParentNode.Checked = true;
                    ParentNode.StateImageIndex = 1;
                }
            }
            finally {
                SetParentState(ParentNode);                         // the parent node becomes 
                                                                    // the current node
            }
        }
    }
    protected void SetChildrenState(TreeNode tNode, bool RootNode) {
        if (!RootNode) {
            tNode.Checked = (tNode.Parent.StateImageIndex == 1);    // the child state 
                                                                    // is inherited
            tNode.StateImageIndex = tNode.Parent.StateImageIndex;   // from the parent state
        }
        foreach (TreeNode ChildNode in tNode.Nodes)
            SetChildrenState(ChildNode, false);
    }
    public void SetState(TreeNode tNode, int NewState) {
        if (NewState < 0 || NewState > 2)
            NewState = 0;
        tNode.Checked = (NewState == 1);
        if (tNode.Checked == (NewState == 1)) {                     // we verify if the checked 
                                                                    // state has
            tNode.StateImageIndex = NewState;                       // not been cancelled in a 
                                                                    // BeforeCheck event

            _bPreventCheckEvent = true;

            SetParentState(tNode);
            SetChildrenState(tNode, true);

            _bPreventCheckEvent = false;
        }
    }

    /// <summary>
    /// Initializes the nodes state.
    /// </summary>

    public void InitializeStates(TreeNodeCollection tNodes) {
        foreach (TreeNode tnCurrent in tNodes) {                   // set tree state image
            if (tnCurrent.StateImageIndex == -1) {                 // to each child node...
                _bPreventCheckEvent = true;

                if (tnCurrent.Parent != null) {
                    tnCurrent.Checked = tnCurrent.Parent.Checked;
                    tnCurrent.StateImageIndex = tnCurrent.Parent.StateImageIndex;
                }
                else
                    tnCurrent.StateImageIndex = tnCurrent.Checked ? 1 : 0;

                _bPreventCheckEvent = false;
            }
            InitializeStates(tnCurrent.Nodes);
        }
    }
    public void InitializeCBImages() {
        if (!CheckBoxes)                        // nothing to do here if
            return;                             // checkboxes are hidden.

        base.CheckBoxes = false;                // hide normal checkboxes...

        InitializeStates(this.Nodes);
    }

    /// <summary>
    /// Refreshes this control.
    /// </summary>

    public override void Refresh() {
        base.Refresh();

        InitializeCBImages();
    }

    // ~~~ events ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    protected override void OnLayout(LayoutEventArgs levent) {
        base.OnLayout(levent);

        InitializeCBImages();
    }

    protected override void OnAfterExpand(TreeViewEventArgs e) {
        if (CheckBoxes)
            InitializeStates(e.Node.Nodes);

        base.OnAfterExpand(e);
    }

    public delegate void AutoCheckEventHandler(object sender, TreeViewEventArgs e);
    public event AutoCheckEventHandler AutoCheck;

    protected override void OnBeforeCheck(TreeViewCancelEventArgs e) {
        if (_bPreventCheckEvent)
            return;

        base.OnBeforeCheck(e);
    }

    protected override void OnAfterCheck(TreeViewEventArgs e) {
        if (_bPreventCheckEvent) {
            if (AutoCheck != null)
                AutoCheck(this, e);
            return;
        }

        base.OnAfterCheck(e);
    }

    protected override void OnNodeMouseClick(TreeNodeMouseClickEventArgs e) {
        base.OnNodeMouseClick(e);

        int iSpacing = ImageList == null ? 0 : 20;      // if user clicked area
        if (e.X > e.Node.Bounds.Left - iSpacing ||       // *not* used by the state
            e.X < e.Node.Bounds.Left - (iSpacing + 14) ||    // image we can leave here.
            e.Button != MouseButtons.Left) {
            return;
        }

        SetState(e.Node, e.Node.Checked ? 0 : 1);
    }
}

History

• 05/03/2012: First submission