Textbox custom onPaint

Question

I'm trying to create a custom onPaint for my textbox, it is working... it is working But when I try to type something, a textbox is rendering above the textbox.

This is my constructor:

public TextBox()
{
  Font = new Font("Segoe UI", 11F, FontStyle.Regular, GraphicsUnit.Point, ((byte)(0)));
  BackColor = Color.White;
  BorderColor = Color.Gray;
  BorderStyle = BorderStyle.None;
  SetStyle(ControlStyles.UserPaint, true);
}

And the onPaint:

protected override void OnPaint(PaintEventArgs e)
{
  Graphics g = e.Graphics;
  g.FillRectangle(backgroundBrush, 0, 0, this.Width, this.Height);

  SizeF fontSize = g.MeasureString(Text, Font);
  g.DrawString(Text, Font, new SolidBrush(ForeColor), new PointF(5, 5), cFormat);

  g.DrawRectangle(borderPen, borderPen.Width / 2, borderPen.Width / 2,
                  this.Width - borderPen.Width, this.Height - borderPen.Width);
}

Answer 1

If you just want a custom TextBox with some custom border (width and color), I have 2 solutions here:

1. Using ControlPaint, this will allow you to draw border with some style and color but can't use Brush to draw more variously (like a HatchBrush can do):

   public class CustomTextBox : TextBox
   {
       [DllImport("user32")]
       private static extern IntPtr GetWindowDC(IntPtr hwnd);
       struct RECT
       {
         public int left, top, right, bottom;
       }
       struct NCCALSIZE_PARAMS
       {
         public RECT newWindow;
         public RECT oldWindow;
         public RECT clientWindow;
         IntPtr windowPos;
       }            
       float clientPadding = 2;  
       float actualBorderWidth = 4;
       Color borderColor = Color.Red;      
       protected override void WndProc(ref Message m)
       {
         //We have to change the clientsize to make room for borders
         //if not, the border is limited in how thick it is.
         if (m.Msg == 0x83) //WM_NCCALCSIZE   
         {
           if (m.WParam == IntPtr.Zero)
           {
               RECT rect = (RECT)Marshal.PtrToStructure(m.LParam, typeof(RECT));
               rect.left += clientPadding;
               rect.right -= clientPadding;
               rect.top += clientPadding;
               rect.bottom -= clientPadding;
               Marshal.StructureToPtr(rect, m.LParam, false);
           }
           else
           {
               NCCALSIZE_PARAMS rects = (NCCALSIZE_PARAMS)Marshal.PtrToStructure(m.LParam, typeof(NCCALSIZE_PARAMS));
               rects.newWindow.left += clientPadding;
               rects.newWindow.right -= clientPadding;
               rects.newWindow.top += clientPadding;
               rects.newWindow.bottom -= clientPadding;
               Marshal.StructureToPtr(rects, m.LParam, false);
           }
         }
         if (m.Msg == 0x85) //WM_NCPAINT    
         {         
            IntPtr wDC = GetWindowDC(Handle);
            using(Graphics g = Graphics.FromHdc(wDC)){                                                      
              ControlPaint.DrawBorder(g, new Rectangle(0,0,Size.Width, Size.Height), borderColor, actualBorderWidth, ButtonBorderStyle.Solid,
            borderColor, actualBorderWidth, ButtonBorderStyle.Solid, borderColor, actualBorderWidth, ButtonBorderStyle.Solid,
            borderColor, actualBorderWidth, ButtonBorderStyle.Solid); 
            }   
            return;          
         }
         base.WndProc(ref m);
       }
   }
   

   Here is the textbox snapshot:

   

2. using FillRegion method of a Graphics to paint the border with various kinds of Brush, here I use HatchBrush:

   public class CustomTextBox : TextBox
   {
     [DllImport("user32")]
     private static extern IntPtr GetWindowDC(IntPtr hwnd);
     struct RECT
     {
       public int left, top, right, bottom;
     }
     struct NCCALSIZE_PARAMS
     {
       public RECT newWindow;
       public RECT oldWindow;
       public RECT clientWindow;
       IntPtr windowPos;
     }         
     int clientPadding = 2;   
     int actualBorderWidth = 4;     
     protected override void WndProc(ref Message m)
     {
         //We have to change the clientsize to make room for borders
         //if not, the border is limited in how thick it is.
         if (m.Msg == 0x83) //WM_NCCALCSIZE   
         {
           if (m.WParam == IntPtr.Zero)
           {
               RECT rect = (RECT)Marshal.PtrToStructure(m.LParam, typeof(RECT));
               rect.left += clientPadding;
               rect.right -= clientPadding;
               rect.top += clientPadding;
               rect.bottom -= clientPadding;
               Marshal.StructureToPtr(rect, m.LParam, false);
           }
           else
           {
               NCCALSIZE_PARAMS rects = (NCCALSIZE_PARAMS)Marshal.PtrToStructure(m.LParam, typeof(NCCALSIZE_PARAMS));
               rects.newWindow.left += clientPadding;
               rects.newWindow.right -= clientPadding;
               rects.newWindow.top += clientPadding;
               rects.newWindow.bottom -= clientPadding;
               Marshal.StructureToPtr(rects, m.LParam, false);
           }
         }
         if (m.Msg == 0x85) //WM_NCPAINT
         {                 
           IntPtr wDC = GetWindowDC(Handle);
           using(Graphics g = Graphics.FromHdc(wDC)){                                                
             Rectangle rect = new Rectangle(0,0,Width,Height);
             Rectangle inner = new Rectangle(0, 0, Width, Height);
             inner.Offset(actualBorderWidth + 2, actualBorderWidth + 2);
             inner.Width -= 2 * actualBorderWidth + 4;
             inner.Height -= 2 * actualBorderWidth + 4;
             Region r = new Region(rect);
             r.Xor(inner);
             using (System.Drawing.Drawing2D.HatchBrush brush = new System.Drawing.Drawing2D.HatchBrush(System.Drawing.Drawing2D.HatchStyle.SmallCheckerBoard, Color.Green, Color.Red))
             {                    
               g.FillRegion(brush, r);
             }
           }
           return;
         }
         base.WndProc(ref m);
     }
   }
   

   Here is the textbox snapshot: