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Multi-Column ComboBox

, 1 Jul 2003
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Implementation of an OwnerDraw MultiColumn ComboBox

Introduction

After submersing myself into the Internet in the endless search of a MultiColumn ComboBox, and trying for 2 years to develop one (in VB6), I have finally got something half-way decent. Some thanks goes out to Carlos H. Perez whose code has shown me how to do some very interesting things! There is not one routine though that has been "copied" from any Project out there, everything has been re-written (mainly because I wanted to learn) and optimized as best I knew how.

Background

The Multi-Column ComboBox is an Owner Drawn control derived from the System.Windows.Forms.ComboBox. However, the control does not use the standard "Items" array within the normal ComboBox. This is where this control excels. Since I was writing my own Control Suite, I needed a way for every Control that had a need for a Collection of Items to be universal among all Controls. Also, I hated Microsoft for taking away Keys from the Collection Classes...so I wrote my own using ideas from the CollectionGen utility. The Collections used within the ComboBox (and also the ListView shown above) are Strongly-Typed and very fast, this enables a fast lookup on the Control using either the Index or the Key of any Item.

One of the harder things to figure out was the HorizontalExtent of the drop-down List. When Items exceed the Horizontal Extent, the Horizontal Scrollbar should appear. I did not find anything anywhere on how to do this, so I did some hacking and came up with a very easy method using the CreateParams property of the control. By setting the WS_HSCROLL style bit, it gives the Control the ability (not the functionality) to have a Horizontal Scrollbar. The tough part is determining how much of a HorizontalExtent to give the drop-down list! I was able to set the HExtent by Overriding the OnDropDown Event of the ComboBox.

Calculating the Horizontal Extent

The Control needed an auto-magic way of Calculating the Horizontal Extent. Since I hate relying on Users to do the "right thing" (or other programmers in this case), I decided to make the Control "smart" enough to handle things where someone leaves off. When adding a ListColumn object to the Control (the Control NEEDS at least 1 ListColumn in order to Display data), if the programmer omits the "Width" Property, the Width will remain at "-1". By leaving the Column with a Width of -1, that Column's Width will be auto-magically calculated based on the Widest Text in that particular Column. If the Column is set to "Visible = False", then it's width will not be added into the Extent.

Using the code

The Control uses a very simple Object Model. It basically works the same way as the ListView does in "Details" mode. First, the ListColumns are added, then the ListItems are added. The ListItem Object supports a ListSubItems Collection which is used to access the other Columns within the Control (again, exactly like the ListView).

'Load the Form
Private Sub FormLoad(ByVal sender As Object, 
    ByVal e As System.EventArgs) Handles MyBase.Load
  With cboBase
    .ListColumns.Add("State ID") 'The Column's Width 
                                 'will be Automatically Calculated
    .ListColumns.Add("State Name") 
				
    For i As Integer = 0 To 19
      .ListItems.Add("Item" & i.ToString, "Item " & i.ToString)
      .ListItems(i).ListSubItems.Add("Item" & i.ToString & ":SubItem 0")
    Next i
  End With
End Sub
		

Points of Interest

Unfortunately, this control does not support DataBinding.  There is one thing that may be very Interesting though.  The Control has a Special Event "FocusChanging".  I needed an Event in one of my interfaces that told me which Direction the User was Tabbing through the Controls.  This allowed me to control which Tab got focus on a TabbedDialog control so that Data Entry would be a lot easier.  When the Event is Raised, it tells which Direction the User has Tabbed.  If you want to Handle that Event, and set Focus to another Control, simply tell the EventArgs that you Handled it (i.e. e.Handled = True). 

Private Sub cboBox3_FocusChanging(ByVal Sender As Object, 
       ByVal e As CodeSamples.Controls.FocusChangeEventArgs) 
       Handles cboBox3.FocusChanging
  If (e.Direction = CodeSamples.Controls.FocusDirection.Forward) Then
    e.Handled = True
    cboBox1.Focus()
  ElseIf (e.Direction = CodeSamples.Controls.FocusDirection.Backward) Then
    e.Handled = True
    cboBox4.Focus()
  End If
End Sub		
		

The other Point of Interest, is that the Control fully supports AutoTyping!  It will only allow Items to be Selected that are in the List.  The Good news is that in VS.NET 2003, Microsoft has FINALLY got the "e.Handled" Property of the "KeyPressEvents" working!  This makes it so that the AutoTyping feature does not flicker anymore!  I have also tried in the past to be able to set a Property so the Developer could choose which Column was Displayed in the Text area.  However, due to some weird functionality of the CombBox (and Inheriting from it), this will have to come when I re-write the entire ComboBox from scratch LOL!

History

License

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About the Author

Tim McCurdy
Web Developer
United States United States
No Biography provided

Comments and Discussions

 
QuestionBehave like normal ComboBox PinmemberMember 111199757-Oct-14 3:42 
QuestionThanks Pinmemberphalin27-Aug-14 18:20 
GeneralItem Highlight FINALLY fixed! PinmemberTim McCurdy10-Feb-11 4:05 
GeneralRe: Item Highlight FINALLY fixed! PinmemberMember 766080210-Feb-11 20:43 
Generalitem cant highlight while control change PinmemberMember 76608029-Feb-11 20:22 
GeneralRe: item cant highlight while control change PinmemberTim McCurdy10-Feb-11 4:05 
GeneralUnable to Select and Item PinmemberDaniel St.3-Oct-07 12:02 
GeneralRe: Unable to Select and Item PinmemberImdabaum3-Dec-10 9:24 
GeneralRe: Unable to Select and Item PinmemberTim McCurdy3-Dec-10 15:50 
Generalaspx PinmemberWrongWayRookieNew18-Dec-06 12:39 
GeneralRe: aspx PinmemberTim McCurdy18-Dec-06 15:34 
Generalwhen I use bounding from datatable. Pinmemberphob12-Sep-06 18:34 
GeneralTypo? in DrawGradient method in Painting.vb PinmemberSBendBuckeye5-Jul-06 14:22 
GeneralRe: Typo? in DrawGradient method in Painting.vb PinmemberTim McCurdy7-Jul-06 7:15 
GeneralDuplicate enumeration values PinmemberSBendBuckeye5-Jul-06 13:15 
GeneralRe: Duplicate enumeration values PinmemberTim McCurdy7-Jul-06 7:13 
GeneralMouse Over Highlight PinmemberAPM Consulting21-May-06 6:26 
GeneralRe: Mouse Over Highlight PinmemberTim McCurdy31-May-06 11:20 
GeneralRe: Mouse Over Highlight PinmemberAPM Consulting9-Jun-06 9:25 
GeneralRe: Mouse Over Highlight Pinmember_Thurein_24-Jul-06 1:35 
GeneralRe: Mouse Over Highlight PinmemberAPM Consulting27-Jul-06 10:32 
GeneralText in ComboBox PinmemberWu ZhiYuan4-Jan-06 16:02 
GeneralRe: Text in ComboBox PinmemberTim McCurdy4-Jan-06 16:33 
NewsAdvanced list box and combo box Pinmemberbrett5630-Nov-05 5:40 
GeneralRe: Advanced list box and combo box Pinmemberdarkbyte2316-Mar-07 17:39 
QuestionHow to customise this coding with Macromedia Dreamweaver 2004 MX Pinmembermoraji23-Nov-05 17:53 
GeneralHandling the Index Property PinmemberGenoJoeInOhio18-Aug-05 16:55 
GeneralRe: Handling the Index Property PinmemberTim McCurdy20-Aug-05 7:52 
GeneralNew Version PinmemberTim McCurdy27-May-05 3:18 
GeneralDisplay from MultiColumn PinmemberOceania24-May-05 11:59 
GeneralRe: Display from MultiColumn PinmemberOceania25-May-05 11:38 
GeneralNeed some help.. I am new.. Pinmemberkekinlim24-Jan-05 22:35 
GeneralNew Version Available PinmemberTim McCurdy25-Nov-04 4:28 
GeneralRe: New Version Available PinmemberHet210921-Jan-05 19:58 
GeneralVietNamese ComboBox Auto DropDown and Auto Focus Item when typing PinmemberHaiNguyenJC20-Nov-04 18:00 
Questionheaders ? Pinmemberfdrebola5-Aug-04 22:37 
AnswerRe: headers ? Pinmembermikasa25-Nov-04 3:53 
GeneralExpanding the drop down list view PinmemberSupaHoopsa19-Jul-04 23:38 
GeneralRe: Expanding the drop down list view Pinmemberjatabar9-Sep-04 14:00 
QuestionImages? Pinmemberatomiton16-Jul-04 11:41 
AnswerRe: Images? Pinmembermikasa2-Nov-04 9:08 
QuestionHow about c# Pinsusslewisv30-Mar-04 7:18 
AnswerRe: How about c# Pinmembersukesh.g26-May-04 19:24 
GeneralHelp - Remove Item PinmemberxvFaithvx11-Feb-04 2:57 
GeneralRe: Help - Remove Item Pinmembermikasa18-Feb-04 9:58 
GeneralRe: Help - Remove Item PinsussAnonymous18-Feb-04 10:06 
GeneralRe: Help - Remove Item Pinmembersukesh.g19-Mar-04 23:24 
GeneralRe: Help - Remove Item PinmemberTim McCurdy25-Nov-04 4:30 
Generalhiya, intresting concept BUT PinmemberRBlyth23-Jan-04 1:42 
GeneralRe: hiya, intresting concept BUT Pinmembermikasa24-Jan-04 9:06 

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