Nella mia esperienza di solito non è possibile. O disegni tu stesso l'elemento o non lo fai. Se provi a comporre la tua grafica sopra quella disegnata dal controllo, finirai con glitch.
E 'un po' di dolore, perché si deve gestire i rettangoli di attivazione, mette in evidenza di selezione e disegno tutti i glifi da soli.
Sul lato positivo, Visual Styles può essere usato per fare la maggior parte del lavoro.
Ecco un codice che ti consente di ottenere il massimo da lì (è incompleto, in quanto utilizza alcuni metodi non inclusi e non rende esattamente ciò che fa una normale vista ad albero perché supporta gli elementi grad e le colonne riempiti, ma dovrebbe essere un utile riferimento)
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);
}
}