How can I override an event method for a combobox control used in my Windows App?

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  Hi,
  
  Here's an example of how to achieve what you want for the down key. For the up key things are similar.
  
  

  1	public partial class Form1 : Form
  2	{
  3	public Form1()
  4	{
  5	InitializeComponent();
  6
  7	for (int i = 0; i < 10; i++)
  8	this.comboBox1.Items.Add(i);
  9
  10	this.comboBox1.KeyDown += new KeyEventHandler(comboBox1_KeyDown);
  11	}
  12
  13	void comboBox1_KeyDown(object sender, KeyEventArgs e)
  14	{
  15	ComboBox c = sender as ComboBox;
  16	if (e.KeyCode == Keys.Down && c.SelectedIndex == c.Items.Count - 1)
  17	{
  18	c.SelectedIndex = 0;
  19	c.SelectAll();
  20	e.SuppressKeyPress = true;
  21	}
  22	}
  23	}

  
  Hope this helps,
  -Tudor
  

  ---

  19 years old student http://www.tudoralex.com

  • Proposed as answer by Tudor Alexandru Thursday, June 19, 2008 10:39 AM
  • Edited by Tudor Alexandru Thursday, June 19, 2008 10:40 AM ----

  Thursday, June 19, 2008 10:38 AM
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  Hi Tudor,
           Thanks for your reply. I already build the logic to perform the required task in KeyDown event. Below is  the code I've wrote for on combo box.
  
  private void cboFactorLevel_KeyDown(object sender, KeyEventArgs e)
          {
              if (cboFactorLevel.Items.Count == 0) return;
              switch (e.KeyValue)
              {
                  case 38:
                      if (cboFactorLevel.SelectedItem == null || cboFactorLevel.SelectedItem.Index == 0)
                      {
                          cboFactorLevel.SelectedItem = cboFactorLevel.Items[cboFactorLevel.Items.Count - 1];
                      }
                      else if (cboFactorLevel.SelectedItem.Index > 0)
                      {
                          cboFactorLevel.SelectedItem = cboFactorLevel.Items[cboFactorLevel.SelectedItem.Index - 1];
                      }
                      break;
  
                  case 40:
                      if (cboFactorLevel.SelectedItem == null || cboFactorLevel.SelectedItem.Index == cboFactorLevel.Items.Count - 1)
                      {
                          cboFactorLevel.SelectedItem = cboFactorLevel.Items[0];
                      }
                      else if (cboFactorLevel.SelectedItem.Index < cboFactorLevel.Items.Count - 1)
                      {
                          cboFactorLevel.SelectedItem = cboFactorLevel.Items[cboFactorLevel.SelectedItem.Index + 1];
                      }
  
                      break;
  
                  default:
                      break;
              }
          }
  
  Now I have plenty of combo boxes in my windows application which forces me to write the same above code for all the combos I have. I tried to override the combobox control by using the below code. Unfortunately it is not working. I created a new class by inheriting the combobox control. Just look the code below. I hope you'll understand it better.
  
  
  public class ComboBox : System.Windows.Forms.ComboBox
      {
          public ComboBox()
          {
             
          }
          protected override void OnKeyDown(System.Windows.Forms.KeyEventArgs e)
          {
              if (this.Items.Count == 0) return;
              switch (e.KeyValue)
              {
                  case 38:
                      if (this.SelectedItem == null || this.SelectedItem.Index == 0)
                      {
                          this.SelectedItem = this.Items[this.Items.Count - 1];
                      }
                      else if (this.SelectedItem.Index > 0)
                      {
                          this.SelectedItem = this.Items[this.SelectedItem.Index - 1];
                      }
                      break;
  
                  case 40:
                      if (this.SelectedItem == null || this.SelectedItem.Index == this.Items.Count - 1)
                      {
                          this.SelectedItem = this.Items[0];
                      }
                      else if (this.SelectedItem.Index < this.Items.Count - 1)
                      {
                          this.SelectedItem = this.Items[this.SelectedItem.Index + 1];
                      }
  
                      break;
  
                  default:
                      break;
              }
              base.OnKeyDown(e);
          }
      }
  
  I think you can guide me better.
  
  Once again thanks for your reply.
  
  With regards,
  SreeRam.
  

  ---

  a dedicated learner

  Thursday, June 19, 2008 10:49 AM
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  Hi again,
  
  Well by combining what I have in my post with what you have in yours, here's a version of the modified combo box:
  
  

  public class ModComboBox : System.Windows.Forms.ComboBox

  {

  public ModComboBox() {}

  protected override void OnKeyDown(System.Windows.Forms.KeyEventArgs e)

  {

  if (this.Items.Count == 0) return;

  if (e.KeyCode == Keys.Down)

  if (this.SelectedIndex == this.Items.Count - 1)

  {

  this.SelectedIndex = 0;

  this.SelectAll();

  e.SuppressKeyPress = true;

  }

  if (e.KeyCode == Keys.Up)

  if (this.SelectedIndex == 0)

  {

  this.SelectedIndex = this.Items.Count - 1;

  this.SelectAll();

  e.SuppressKeyPress = true;

  }

  }

  }

  
  Hope this helps,
  -Tudor
  

  ---

  19 years old student http://www.tudoralex.com

  • Proposed as answer by Tudor Alexandru Thursday, June 19, 2008 1:52 PM
  • Marked as answer by SreeRamaSaran Mullapudi Friday, June 20, 2008 7:22 AM

  Thursday, June 19, 2008 1:51 PM
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  Thanks Mr. Tudor
               Could I use a partial class instead of using a brand new class for the above purpose to avoid initialization of this new class? If yes plz let me know how could i achieve it? I tried the previous code you suggested me and it's working fine. But It doesn't support the designer. To use this we have to add the controls programatically. I got another thought that if I use the same control without inheriting the combobox control it looks fine and it saves the time. For that purpose I want to use the partial class and just override the onkeydown event method. I tried it but it doesn't work. Could plz tell me how it will be achieved? If you suggest me any article to accomplish this I am ready to learn anything to get the job done.
  
  awaiting for your reply.
  
  Thanks a lot.
  
  With regards,
  SreeRam.
  

  ---

  a dedicated learner

  Friday, June 20, 2008 7:31 AM
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  For questions and discussions regarding client application development using Windows Forms controls and features, please see http://forums.microsoft.com/msdn/ShowForum.aspx?ForumID=8&SiteID=1
  

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  http://www.peterRitchie.com/blog

  Friday, June 20, 2008 1:52 PM