DrawTreeNodeEventArgs Class

Definition

Namespace:

System.Windows.Forms

Assembly:

System.Windows.Forms.dll

Provides data for the DrawNode event.

public ref class DrawTreeNodeEventArgs : EventArgs

public class DrawTreeNodeEventArgs : EventArgs

type DrawTreeNodeEventArgs = class
    inherit EventArgs

Public Class DrawTreeNodeEventArgs
Inherits EventArgs

Inheritance

Object

EventArgs

DrawTreeNodeEventArgs

Examples

The following code example demonstrates how to customize a TreeView control using owner drawing. The TreeView control in the example displays optional node tags alongside the standard node labels. Node tags are specified using the TreeNode.Tag property. The TreeView control also uses custom colors, including a custom highlight color.

You can customize most of the TreeView colors by setting color properties, but the selection highlight color is not available as a property. Additionally, the default selection highlight rectangle extends only around a node label. Owner drawing must be used to draw the node tags and to draw a customized highlight rectangle large enough to include a node tag.

In the example, a handler for the TreeView.DrawNode event draws the node tags and the custom selection highlight manually. Unselected nodes do not need customization. For these, the DrawDefault property is set to true so that they will be drawn by the operating system.

Additionally, a handler for the Control.MouseDown event provides hit-testing. By default, a node can be selected only by clicking the region around its label. The Control.MouseDown event handler selects a node that is clicked anywhere within this region or within the region around a node tag, if present.

#using <System.dll>
#using <System.Windows.Forms.dll>
#using <System.Drawing.dll>

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
public ref class TreeViewOwnerDraw: public Form
{
private:
   TreeView^ myTreeView;

   // Create a Font object for the node tags.
   System::Drawing::Font^ tagFont;

public:

   TreeViewOwnerDraw()
   {
      tagFont = gcnew System::Drawing::Font( "Helvetica",8,FontStyle::Bold );

      // Create and initialize the TreeView control.
      myTreeView = gcnew TreeView;
      myTreeView->Dock = DockStyle::Fill;
      myTreeView->BackColor = Color::Tan;
      myTreeView->CheckBoxes = true;
      
      // Add nodes to the TreeView control.
      TreeNode^ node;
      for ( int x = 1; x < 4; ++x )
      {
         // Add a root node to the TreeView control.
         node = myTreeView->Nodes->Add( String::Format( "Task {0}", x ) );
         for ( int y = 1; y < 4; ++y )
         {
            // Add a child node to the root node.
            node->Nodes->Add( String::Format( "Subtask {0}", y ) );
         }
      }
      myTreeView->ExpandAll();
      
      // Add tags containing alert messages to a few nodes 
      // and set the node background color to highlight them.
      myTreeView->Nodes[ 1 ]->Nodes[ 0 ]->Tag = "urgent!";
      myTreeView->Nodes[ 1 ]->Nodes[ 0 ]->BackColor = Color::Yellow;
      myTreeView->SelectedNode = myTreeView->Nodes[ 1 ]->Nodes[ 0 ];
      myTreeView->Nodes[ 2 ]->Nodes[ 1 ]->Tag = "urgent!";
      myTreeView->Nodes[ 2 ]->Nodes[ 1 ]->BackColor = Color::Yellow;
      
      // Configure the TreeView control for owner-draw and add
      // a handler for the DrawNode event.
      myTreeView->DrawMode = TreeViewDrawMode::OwnerDrawText;
      myTreeView->DrawNode += gcnew DrawTreeNodeEventHandler( this, &TreeViewOwnerDraw::myTreeView_DrawNode );
      
      // Add a handler for the MouseDown event so that a node can be 
      // selected by clicking the tag text as well as the node text.
      myTreeView->MouseDown += gcnew MouseEventHandler( this, &TreeViewOwnerDraw::myTreeView_MouseDown );
      
      // Initialize the form and add the TreeView control to it.
      this->ClientSize = System::Drawing::Size( 292, 273 );
      this->Controls->Add( myTreeView );
   }

protected:
   // Clean up any resources being used.        
   ~TreeViewOwnerDraw()
   {
      if ( tagFont != nullptr )
      {
         delete tagFont;
      }
   }

   // Draws a node.
private:
   void myTreeView_DrawNode( Object^ sender, DrawTreeNodeEventArgs^ e )
   {
      // Draw the background and node text for a selected node.
      if ( (e->State & TreeNodeStates::Selected) != (TreeNodeStates)0 )
      {
         // Draw the background of the selected node. The NodeBounds
         // method makes the highlight rectangle large enough to
         // include the text of a node tag, if one is present.
         e->Graphics->FillRectangle( Brushes::Green, NodeBounds( e->Node ) );

         // Retrieve the node font. If the node font has not been set,
         // use the TreeView font.
         System::Drawing::Font^ nodeFont = e->Node->NodeFont;
         if ( nodeFont == nullptr )
                  nodeFont = (dynamic_cast<TreeView^>(sender))->Font;

         // Draw the node text.
         e->Graphics->DrawString( e->Node->Text, nodeFont, Brushes::White, Rectangle::Inflate( e->Bounds, 2, 0 ) );
      }
      // Use the default background and node text.
      else
      {
         e->DrawDefault = true;
      }

      // If a node tag is present, draw its string representation 
      // to the right of the label text.
      if ( e->Node->Tag != nullptr )
      {
         e->Graphics->DrawString( e->Node->Tag->ToString(), tagFont, Brushes::Yellow, (float)e->Bounds.Right + 2, (float)e->Bounds.Top );
      }

      
      // If the node has focus, draw the focus rectangle large, making
      // it large enough to include the text of the node tag, if present.
      if ( (e->State & TreeNodeStates::Focused) != (TreeNodeStates)0 )
      {
         Pen^ focusPen = gcnew Pen( Color::Black );
         try
         {
            focusPen->DashStyle = System::Drawing::Drawing2D::DashStyle::Dot;
            Rectangle focusBounds = NodeBounds( e->Node );
            focusBounds.Size = System::Drawing::Size( focusBounds.Width - 1, focusBounds.Height - 1 );
            e->Graphics->DrawRectangle( focusPen, focusBounds );
         }
         finally
         {
            if ( focusPen )
               delete safe_cast<IDisposable^>(focusPen);
         }

      }
   }

   // Selects a node that is clicked on its label or tag text.
   void myTreeView_MouseDown( Object^ /*sender*/, MouseEventArgs^ e )
   {
      TreeNode^ clickedNode = myTreeView->GetNodeAt( e->X, e->Y );
      if ( NodeBounds( clickedNode ).Contains( e->X, e->Y ) )
      {
         myTreeView->SelectedNode = clickedNode;
      }
   }

   // Returns the bounds of the specified node, including the region 
   // occupied by the node label and any node tag displayed.
   Rectangle NodeBounds( TreeNode^ node )
   {
      // Set the return value to the normal node bounds.
      Rectangle bounds = node->Bounds;
      if ( node->Tag != nullptr )
      {
         // Retrieve a Graphics object from the TreeView handle
         // and use it to calculate the display width of the tag.
         Graphics^ g = myTreeView->CreateGraphics();
         int tagWidth = (int)g->MeasureString( node->Tag->ToString(), tagFont ).Width + 6;
         
         // Adjust the node bounds using the calculated value.
         bounds.Offset( tagWidth / 2, 0 );
         bounds = Rectangle::Inflate( bounds, tagWidth / 2, 0 );
         g->~Graphics();
      }

      return bounds;
   }
};

[STAThreadAttribute]
int main()
{
   Application::Run( gcnew TreeViewOwnerDraw );
}

using System;
using System.Drawing;
using System.Windows.Forms;

public class TreeViewOwnerDraw : Form
{
    private TreeView myTreeView;

    // Create a Font object for the node tags.
    Font tagFont = new Font("Helvetica", 8, FontStyle.Bold);

    public TreeViewOwnerDraw()
    {
        // Create and initialize the TreeView control.
        myTreeView = new TreeView();
        myTreeView.Dock = DockStyle.Fill;
        myTreeView.BackColor = Color.Tan;
        myTreeView.CheckBoxes = true;

        // Add nodes to the TreeView control.
        TreeNode node;
        for (int x = 1; x < 4; ++x)
        {
            // Add a root node to the TreeView control.
            node = myTreeView.Nodes.Add(String.Format("Task {0}", x));
            for (int y = 1; y < 4; ++y)
            {
                // Add a child node to the root node.
                node.Nodes.Add(String.Format("Subtask {0}", y));
            }
        }
        myTreeView.ExpandAll();

        // Add tags containing alert messages to a few nodes 
        // and set the node background color to highlight them.
        myTreeView.Nodes[1].Nodes[0].Tag = "urgent!";
        myTreeView.Nodes[1].Nodes[0].BackColor = Color.Yellow;
        myTreeView.SelectedNode = myTreeView.Nodes[1].Nodes[0];
        myTreeView.Nodes[2].Nodes[1].Tag = "urgent!";
        myTreeView.Nodes[2].Nodes[1].BackColor = Color.Yellow;

        // Configure the TreeView control for owner-draw and add
        // a handler for the DrawNode event.
        myTreeView.DrawMode = TreeViewDrawMode.OwnerDrawText;
        myTreeView.DrawNode += 
            new DrawTreeNodeEventHandler(myTreeView_DrawNode);

        // Add a handler for the MouseDown event so that a node can be 
        // selected by clicking the tag text as well as the node text.
        myTreeView.MouseDown += new MouseEventHandler(myTreeView_MouseDown);

        // Initialize the form and add the TreeView control to it.
        this.ClientSize = new Size(292, 273);
        this.Controls.Add(myTreeView);
    }

    // Clean up any resources being used.        
    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            tagFont.Dispose();
        }
        base.Dispose(disposing);
    }

    [STAThreadAttribute()]
    static void Main() 
    {
        Application.Run(new TreeViewOwnerDraw());
    }

    // Draws a node.
    private void myTreeView_DrawNode(
        object sender, DrawTreeNodeEventArgs e)
    {
        // Draw the background and node text for a selected node.
        if ((e.State & TreeNodeStates.Selected) != 0)
        {
            // Draw the background of the selected node. The NodeBounds
            // method makes the highlight rectangle large enough to
            // include the text of a node tag, if one is present.
            e.Graphics.FillRectangle(Brushes.Green, NodeBounds(e.Node));

            // Retrieve the node font. If the node font has not been set,
            // use the TreeView font.
            Font nodeFont = e.Node.NodeFont;
            if (nodeFont == null) nodeFont = ((TreeView)sender).Font;

            // Draw the node text.
            e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White,
                Rectangle.Inflate(e.Bounds, 2, 0));
        }

        // Use the default background and node text.
        else 
        {
            e.DrawDefault = true;
        }

        // If a node tag is present, draw its string representation 
        // to the right of the label text.
        if (e.Node.Tag != null)
        {
            e.Graphics.DrawString(e.Node.Tag.ToString(), tagFont,
                Brushes.Yellow, e.Bounds.Right + 2, e.Bounds.Top);
        }

        // If the node has focus, draw the focus rectangle large, making
        // it large enough to include the text of the node tag, if present.
        if ((e.State & TreeNodeStates.Focused) != 0)
        {
            using (Pen focusPen = new Pen(Color.Black))
            {
                focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
                Rectangle focusBounds = NodeBounds(e.Node);
                focusBounds.Size = new Size(focusBounds.Width - 1, 
                focusBounds.Height - 1);
                e.Graphics.DrawRectangle(focusPen, focusBounds);
            }
        }
    }

    // Selects a node that is clicked on its label or tag text.
    private void myTreeView_MouseDown(object sender, MouseEventArgs e)
    {
        TreeNode clickedNode = myTreeView.GetNodeAt(e.X, e.Y);
        if (NodeBounds(clickedNode).Contains(e.X, e.Y))
        {
            myTreeView.SelectedNode = clickedNode;
        }
    }

    // Returns the bounds of the specified node, including the region 
    // occupied by the node label and any node tag displayed.
    private Rectangle NodeBounds(TreeNode node)
    {
        // Set the return value to the normal node bounds.
        Rectangle bounds = node.Bounds;
        if (node.Tag != null)
        {
            // Retrieve a Graphics object from the TreeView handle
            // and use it to calculate the display width of the tag.
            Graphics g = myTreeView.CreateGraphics(); 
            int tagWidth = (int)g.MeasureString
                (node.Tag.ToString(), tagFont).Width + 6;

            // Adjust the node bounds using the calculated value.
            bounds.Offset(tagWidth/2, 0);
            bounds = Rectangle.Inflate(bounds, tagWidth/2, 0);
            g.Dispose();
         }
        
        return bounds;
    }
}

Imports System.Drawing
Imports System.Windows.Forms

Public Class TreeViewOwnerDraw
    Inherits Form

    Private WithEvents myTreeView As TreeView
    
    ' Create a Font object for the node tags.
    Private tagFont As New Font("Helvetica", 8, FontStyle.Bold)
    
    Public Sub New()

        ' Create and initialize the TreeView control.
        myTreeView = New TreeView()
        myTreeView.Dock = DockStyle.Fill
        myTreeView.BackColor = Color.Tan
        myTreeView.CheckBoxes = True
        
        ' Add nodes to the TreeView control.
        Dim node As TreeNode
        Dim x As Integer
        For x = 1 To 3

            ' Add a root node to the TreeView control.
            node = myTreeView.Nodes.Add(String.Format("Task {0}", x))
            Dim y As Integer
            For y = 1 To 3 

                ' Add a child node to the root node.
                node.Nodes.Add(String.Format("Subtask {0}", y))
            Next y
        Next x
        myTreeView.ExpandAll()
        
        ' Add tags containing alert messages to a few nodes 
        ' and set the node background color to highlight them.
        myTreeView.Nodes(1).Nodes(0).Tag = "urgent!"
        myTreeView.Nodes(1).Nodes(0).BackColor = Color.Yellow
        myTreeView.SelectedNode = myTreeView.Nodes(1).Nodes(0)
        myTreeView.Nodes(2).Nodes(1).Tag = "urgent!"
        myTreeView.Nodes(2).Nodes(1).BackColor = Color.Yellow
        
        ' Configure the TreeView control for owner-draw.
        myTreeView.DrawMode = TreeViewDrawMode.OwnerDrawText

        ' Add a handler for the MouseDown event so that a node can be 
        ' selected by clicking the tag text as well as the node text.
        AddHandler myTreeView.MouseDown, AddressOf myTreeView_MouseDown
        
        ' Initialize the form and add the TreeView control to it.
        Me.ClientSize = New Size(292, 273)
        Me.Controls.Add(myTreeView)
    End Sub
    
    <STAThreadAttribute()> _
    Shared Sub Main()
        Application.Run(New TreeViewOwnerDraw())
    End Sub
    
    ' Draws a node.
    Private Sub myTreeView_DrawNode(ByVal sender As Object, _
        ByVal e As DrawTreeNodeEventArgs) Handles myTreeView.DrawNode

        ' Draw the background and node text for a selected node.
        If (e.State And TreeNodeStates.Selected) <> 0 Then

            ' Draw the background of the selected node. The NodeBounds
            ' method makes the highlight rectangle large enough to
            ' include the text of a node tag, if one is present.
            e.Graphics.FillRectangle(Brushes.Green, NodeBounds(e.Node))

            ' Retrieve the node font. If the node font has not been set,
            ' use the TreeView font.
            Dim nodeFont As Font = e.Node.NodeFont
            If nodeFont Is Nothing Then
                nodeFont = CType(sender, TreeView).Font
            End If

            ' Draw the node text.
            e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White, _
                e.Bounds.Left - 2, e.Bounds.Top)

        ' Use the default background and node text.
        Else
            e.DrawDefault = True
        End If

        ' If a node tag is present, draw its string representation 
        ' to the right of the label text.
        If (e.Node.Tag IsNot Nothing) Then
            e.Graphics.DrawString(e.Node.Tag.ToString(), tagFont, _
                Brushes.Yellow, e.Bounds.Right + 2, e.Bounds.Top)
        End If

        ' If the node has focus, draw the focus rectangle large, making
        ' it large enough to include the text of the node tag, if present.
        If (e.State And TreeNodeStates.Focused) <> 0 Then
            Dim focusPen As New Pen(Color.Black)
            Try
                focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot
                Dim focusBounds As Rectangle = NodeBounds(e.Node)
                focusBounds.Size = New Size(focusBounds.Width - 1, _
                    focusBounds.Height - 1)
                e.Graphics.DrawRectangle(focusPen, focusBounds)
            Finally
                focusPen.Dispose()
            End Try
        End If

    End Sub

    ' Selects a node that is clicked on its label or tag text.
    Private Sub myTreeView_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs)
        Dim clickedNode As TreeNode = myTreeView.GetNodeAt(e.X, e.Y)
        If NodeBounds(clickedNode).Contains(e.X, e.Y) Then
            myTreeView.SelectedNode = clickedNode
        End If
    End Sub

    ' Returns the bounds of the specified node, including the region 
    ' occupied by the node label and any node tag displayed.
    Private Function NodeBounds(ByVal node As TreeNode) As Rectangle

        ' Set the return value to the normal node bounds.
        Dim bounds As Rectangle = node.Bounds
        If (node.Tag IsNot Nothing) Then

            ' Retrieve a Graphics object from the TreeView handle
            ' and use it to calculate the display width of the tag.
            Dim g As Graphics = myTreeView.CreateGraphics()
            Dim tagWidth As Integer = CInt(g.MeasureString( _
                node.Tag.ToString(), tagFont).Width) + 6

            ' Adjust the node bounds using the calculated value.
            bounds.Offset(tagWidth \ 2, 0)
            bounds = Rectangle.Inflate(bounds, tagWidth \ 2, 0)
            g.Dispose()
        End If
        Return bounds
    End Function 'NodeBounds

End Class

Remarks

Use the DrawNode event to customize the appearance of nodes in a TreeView control using owner drawing.

The DrawNode event is raised by a TreeView control when its TreeView.DrawMode property is set to TreeViewDrawMode.OwnerDrawAll or TreeViewDrawMode.OwnerDrawText and a node is displayed or updated. The DrawTreeNodeEventArgs passed to the event handler contains information about the node to draw as well as providing methods to help you draw the node.

Use the State or Node properties to retrieve information about the node to draw. Use the Graphics property to do the actual drawing within the area specified by the Bounds property. To make the operating system draw a node that does not need to be owner drawn, set the DrawDefault property to true.

When the TreeView.DrawMode property is set to TreeViewDrawMode.OwnerDrawText, the area indicated by the Bounds property includes the label portion of the node only. When the TreeView.DrawMode property is set to TreeViewDrawMode.OwnerDrawAll, the Bounds area includes the entire node, including the area typically used for icons, checkboxes, plus and minus signs, and lines connecting the nodes.

Constructors

DrawTreeNodeEventArgs(Graphics, TreeNode, Rectangle, TreeNodeStates)

Initializes a new instance of the DrawTreeNodeEventArgs class.

Properties

Bounds	Gets the size and location of the TreeNode to draw.
DrawDefault	Gets or sets a value indicating whether the TreeNode should be drawn by the operating system rather than being owner drawn.
Graphics	Gets the Graphics object used to draw the TreeNode.
Node	Gets the TreeNode to draw.
State	Gets the current state of the TreeNode to draw.

Methods

Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• TreeView
• DrawMode
• DrawNode
• TreeViewDrawMode