D'après mon expérience, vous ne pouvez habituellement pas. Soit vous dessinez l'objet vous-même, soit vous ne le faites pas. Si vous essayez de composer vos graphiques en plus de ceux dessinés par le contrôle, vous finirez avec des problèmes.
C'est un peu pénible car vous devez gérer des rectangles de mise au point, des surlignages de sélection et dessiner vous-même tous les glyphes. Du côté positif, Visual Styles peut être utilisé pour faire la plupart du travail.
Voici un peu de code qui vous permettra d'y arriver (c'est incomplet, car il utilise des méthodes non incluses, et il ne rend pas exactement ce que fait un treeview normal car il prend en charge les items et les colonnes remplis, mais devrait être une référence pratique)
protected virtual void OnDrawTreeNode(object sender, DrawTreeNodeEventArgs e)
{
string text = e.Node.Text;
Rectangle itemRect = e.Bounds;
if (e.Bounds.Height < 1 || e.Bounds.Width < 1)
return;
int cIndentBy = 19; // TODO - support Indent value
int cMargin = 6; // TODO - this is a bit random, it's slaved off the Indent in some way
int cTwoMargins = cMargin * 2;
int indent = (e.Node.Level * cIndentBy) + cMargin;
int iconLeft = indent; // Where to draw parentage lines & icon/checkbox
int textLeft = iconLeft + 16; // Where to draw text
Color leftColour = e.Node.BackColor;
Color textColour = e.Node.ForeColor;
if (Bitfield.IsBitSet(e.State, TreeNodeStates.Grayed))
textColour = Color.FromArgb(255,128,128,128);
// Grad-fill the background
Brush backBrush = new SolidBrush(leftColour);
e.Graphics.FillRectangle(backBrush, itemRect);
// Faint underline along the bottom of each item
Color separatorColor = ColourUtils.Mix(leftColour, Color.FromArgb(255,0,0,0), 0.02);
Pen separatorPen = new Pen(separatorColor);
e.Graphics.DrawLine(separatorPen, itemRect.Left, itemRect.Bottom-1, itemRect.Right, itemRect.Bottom-1);
// Bodged to use Button styles as Treeview styles not available on my laptop...
if (!HideSelection)
{
if (Bitfield.IsBitSet(e.State, TreeNodeStates.Selected) || Bitfield.IsBitSet(e.State, TreeNodeStates.Hot))
{
Rectangle selRect = new Rectangle(textLeft, itemRect.Top, itemRect.Right - textLeft, itemRect.Height);
VisualStyleRenderer renderer = new VisualStyleRenderer((ContainsFocus) ? VisualStyleElement.Button.PushButton.Hot
: VisualStyleElement.Button.PushButton.Normal);
renderer.DrawBackground(e.Graphics, selRect);
// Bodge to make VisualStyle look like Explorer selections - overdraw with alpha'd white rectangle to fade the colour a lot
Brush bodge = new SolidBrush(Color.FromArgb((Bitfield.IsBitSet(e.State, TreeNodeStates.Hot)) ? 224 : 128,255,255,255));
e.Graphics.FillRectangle(bodge, selRect);
}
}
Pen dotPen = new Pen(Color.FromArgb(128,128,128));
dotPen.DashStyle = DashStyle.Dot;
int midY = (itemRect.Top + itemRect.Bottom)/2;
// Draw parentage lines
if (ShowLines)
{
int x = cMargin * 2;
if (e.Node.Level == 0 && e.Node.PrevNode == null)
{
// The very first node in the tree has a half-height line
e.Graphics.DrawLine(dotPen, x, midY, x, itemRect.Bottom);
}
else
{
TreeNode testNode = e.Node; // Used to only draw lines to nodes with Next Siblings, as in normal TreeViews
for (int iLine = e.Node.Level; iLine >= 0; iLine--)
{
if (testNode.NextNode != null)
{
x = (iLine * cIndentBy) + (cMargin * 2);
e.Graphics.DrawLine(dotPen, x, itemRect.Top, x, itemRect.Bottom);
}
testNode = testNode.Parent;
}
x = (e.Node.Level * cIndentBy) + cTwoMargins;
e.Graphics.DrawLine(dotPen, x, itemRect.Top, x, midY);
}
e.Graphics.DrawLine(dotPen, iconLeft + cMargin, midY, iconLeft + cMargin + 10, midY);
}
// Draw Expand (plus/minus) icon if required
if (ShowPlusMinus && e.Node.Nodes.Count > 0)
{
// Use the VisualStyles renderer to use the proper OS-defined glyphs
Rectangle expandRect = new Rectangle(iconLeft-1, midY - 7, 16, 16);
VisualStyleElement element = (e.Node.IsExpanded) ? VisualStyleElement.TreeView.Glyph.Opened
: VisualStyleElement.TreeView.Glyph.Closed;
VisualStyleRenderer renderer = new VisualStyleRenderer(element);
renderer.DrawBackground(e.Graphics, expandRect);
}
// Draw the text, which is separated into columns by | characters
Point textStartPos = new Point(itemRect.Left + textLeft, itemRect.Top);
Point textPos = new Point(textStartPos.X, textStartPos.Y);
Font textFont = e.Node.NodeFont; // Get the font for the item, or failing that, for this control
if (textFont == null)
textFont = Font;
StringFormat drawFormat = new StringFormat();
drawFormat.Alignment = StringAlignment.Near;
drawFormat.LineAlignment = StringAlignment.Center;
drawFormat.FormatFlags = StringFormatFlags.NoWrap;
string [] columnTextList = text.Split('|');
for (int iCol = 0; iCol < columnTextList.GetLength(0); iCol++)
{
Rectangle textRect = new Rectangle(textPos.X, textPos.Y, itemRect.Right - textPos.X, itemRect.Bottom - textPos.Y);
if (mColumnImageList != null && mColumnImageList[iCol] != null)
{
// This column has an imagelist assigned, so we use the column text as an integer zero-based index
// into the imagelist to indicate the icon to display
int iImage = 0;
try
{
iImage = MathUtils.Clamp(Convert.ToInt32(columnTextList[iCol]), 0, mColumnImageList[iCol].Images.Count);
}
catch(Exception)
{
iImage = 0;
}
e.Graphics.DrawImageUnscaled(mColumnImageList[iCol].Images[iImage], textRect.Left, textRect.Top);
}
else
e.Graphics.DrawString(columnTextList[iCol], textFont, new SolidBrush(textColour), textRect, drawFormat);
textPos.X += mColumnWidthList[iCol];
}
// Draw Focussing box around the text
if (e.State == TreeNodeStates.Focused)
{
SizeF size = e.Graphics.MeasureString(text, textFont);
size.Width = (ClientRectangle.Width - 2) - textStartPos.X;
size.Height += 1;
Rectangle rect = new Rectangle(textStartPos, size.ToSize());
e.Graphics.DrawRectangle(dotPen, rect);
// ControlPaint.DrawFocusRectangle(e.Graphics, Rect);
}
}