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;

}

}