TreeView.DrawNode Event 官方指南

https://msdn.microsoft.com/en-us/library/system.windows.forms.treeview.drawnode.aspx

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;    }}