WinForm------TreeList修改节点图标和按钮样式

https://documentation.devexpress.com/#WindowsForms/DevExpressXtraTreeListTreeList_CustomDrawNodeButtontopic

private void treeList1_CustomDrawNodeImages(object sender, DevExpress.XtraTreeList.CustomDrawNodeImagesEventArgs e)
        {
            if (e.Node.Nodes.Count > 0)
            {
                if (e.Node.Expanded)
                {
                    e.SelectImageIndex = 2;
                    return;
                }
                e.SelectImageIndex = 1;
            }
            else
            {
                e.SelectImageIndex = 0;
            }
        }

private void treeList1_CustomDrawNodeButton(object sender, DevExpress.XtraTreeList.CustomDrawNodeButtonEventArgs e)
        {
            Rectangle rect = Rectangle.Inflate(e.Bounds, 0, -2);

            // painting background
            Brush backBrush = new LinearGradientBrush(rect, Color.Blue, Color.LightSkyBlue,
              LinearGradientMode.ForwardDiagonal);
            
            //填充指定矩形内部
            e.Graphics.FillRectangle(backBrush, rect);
            
            //绘画3D边框
            ControlPaint.DrawBorder3D(e.Graphics, rect, Border3DStyle.RaisedOuter);

            //要显示的图画
            string displayCharacter = e.Expanded ? "-" : "+";

            //水平,垂直居中
            StringFormat outCharacterFormat = new StringFormat();
            outCharacterFormat.Alignment = StringAlignment.Center;
            outCharacterFormat.LineAlignment = StringAlignment.Center;

            //绘画图标
            e.Graphics.DrawString(displayCharacter, new Font("Verdana", 8, FontStyle.Bold),
              new SolidBrush(Color.White), rect, outCharacterFormat);

            // 禁止默认的图标显示
            e.Handled = true;
        }