Treeview控件失去焦点，将选择的节点设置为高亮显示

1. 修改TreeView的属性
   

   this.treeView1.HideSelection = false;
   this.treeView1.DrawMode = TreeViewDrawMode.OwnerDrawText;

2. 添加treeView1_DrawNode事件

   private void treeView1_DrawNode(object sender, DrawTreeNodeEventArgs e)
   {
     e.DrawDefault = true;//由操作系统绘制节点，默认值为false
   }

   private void treeView1_DrawNode(object sender, DrawTreeNodeEventArgs e)
   {
       if ((e.State & TreeNodeStates.Selected) != 0)
       {
           e.Graphics.FillRectangle(Brushes.DodgerBlue, e.Node.Bounds);
   
           Font nodeFont = e.Node.NodeFont;
           if (nodeFont == null) nodeFont = ((TreeView)sender).Font;
           e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White, Rectangle.Inflate(e.Bounds, 2, 0));
       }
       else
       {
           e.DrawDefault = true;
       }
   
       if ((e.State & TreeNodeStates.Focused) != 0)
       {
           using (Pen focusPen = new Pen(Color.White))
           {
               focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
               Rectangle focusBounds = e.Node.Bounds;
               focusBounds.Size = new Size(focusBounds.Width - 1,
               focusBounds.Height - 1);
               e.Graphics.DrawRectangle(focusPen, focusBounds);
           }
       }
   }