.net - DateTimePicker automatically move to next datepart

Question

Currently, when using the datetimepicker, after you enter the month you have to either hit the right arrow or the "/" for it to move to the day. Is there a property that I can set or a way to know that the month is done and move to the day and move to the year after the user is done with the day? This is the same behavior with applications written in the old FoxPro/Clipper days.

Answer 1

As @Wael Dalloul says, there is no property to do what you want. After a lot of fiddling and Spy++ work, I came upon the following solution:

1. Inheriting from System.Windows.Forms.DateTimePicker, and declaring private fields for flags:

   public class DPDateTimePicker : DateTimePicker
   {
       private bool selectionComplete = false;
       private bool numberKeyPressed = false;
   

2. Defining constants and structs for Win API:

       private const int WM_KEYUP = 0x0101;
       private const int WM_KEYDOWN = 0x0100;
       private const int WM_REFLECT = 0x2000;
       private const int WM_NOTIFY = 0x004e;
   
       [StructLayout(LayoutKind.Sequential)]
       private struct NMHDR
       {
          public IntPtr hwndFrom;
          public IntPtr idFrom;
          public int Code;
       }    
   

   It's also necessary to include a using statement for System.Runtime.InteropServices in order to use Win API.

3. Override OnKeyDown and set or clear a flag based on if the key pressed was a number (and clear the second flag below).

   protected override void OnKeyDown(KeyEventArgs e)
   {
       numberKeyPressed = (e.Modifiers == Keys.None && ((e.KeyCode >= Keys.D0 && e.KeyCode <= Keys.D9) || (e.KeyCode != Keys.Back && e.KeyCode >= Keys.NumPad0 && e.KeyCode <= Keys.NumPad9)));
       selectionComplete = false;
       base.OnKeyDown(e);
   }
   

4. Override WndProc and trap the WM_REFLECT+WM_NOTIFY message, extract the NMHDR from lParam, then set another flag if the code is -759 (this event is triggered after one of the fields is completely filled in with the keyboard and a date is selected).

   protected override void WndProc(ref Message m)
   {
       if (m.Msg == WM_REFLECT + WM_NOTIFY)
       {
           var hdr = (NMHDR)m.GetLParam(typeof(NMHDR));
           if (hdr.Code == -759) //date chosen (by keyboard)
               selectionComplete = true;
       }
       base.WndProc(ref m);
   }
   

5. Override OnKeyUp and if both flags are set and the key pressed was a number, manually call base.WndProc with a WM_KEYDOWN followed by a WM_KEYUP with Keys.Right, then clear your flags. You can set the lParam of these messages to 0 and not worry about it, and HWnd is of course this.Handle.

   protected override void OnKeyUp(KeyEventArgs e)
   {
       base.OnKeyUp(e);
       if (numberKeyPressed && selectionComplete &&
           (e.Modifiers == Keys.None && ((e.KeyCode >= Keys.D0 && e.KeyCode <= Keys.D9) || (e.KeyCode != Keys.Back && e.KeyCode >= Keys.NumPad0 && e.KeyCode <= Keys.NumPad9))))
       {
           Message m = new Message();
           m.HWnd = this.Handle;
           m.LParam = IntPtr.Zero;
           m.WParam = new IntPtr((int)Keys.Right); //right arrow key
           m.Msg = WM_KEYDOWN;
           base.WndProc(ref m);
           m.Msg = WM_KEYUP;
           base.WndProc(ref m);
           numberKeyPressed = false;
           selectionComplete = false;
       }
   }
   

Apologies for the lack of blank lines in the code, but it wouldn't display right with the blank lines, so I took them out. Trust me, this is the more readable version.