VBLikeCombo - A Visual Basic Style Combo Box

Download demo project - 22 Kb

Download source files - 5 Kb

Introduction

CgzCombo extends the CComboBox class to give ComboBox functionality similar to a Visual Basic combo box with the following features:

• Two "columns": 1 visible and 1 hidden "index column"
• Autoselect: from list box items. Based nearly entirely from example given by Chris Maunder
• Notification: Sends a CBN_CLOSEUP message to parent window when user makes a valid selection using the mouse *or* by typing and moving off control.
• Validation: will not let a user leave the control without a valid selection this is easy to modify if not appropriate for your app.
• Escape key: pressing escape within combo box resets it to value it had when it first got the focus.
• Note: you can easily modify to have both columns hidden and display a third text string. (which is why the stringlist is done the way it is) It's also quite easy to add more "columns".

The class name is CgzCombo.

How to use this control

(assuming you already have a combo box control in a project)

1. Copy gzcombo.h and gzcombo.cpp to your projects directory
2. In visual studio click on Project->Add to project -> Files and select the two files you just copied to your project directory.
3. Add the following line to the header file containing the definition of your CComboBox variable:
   #include "gzcombo.h"
4. In the same header file, change the type of your combo box variable from CComboBox to CgzCombo.
5. Handle ON_CBN_CLOSEUP in your app if you want to act immediately upon valid selection by user, otherwise...dont.

There are only 4 extra functions you call to interact with the control:

//Add items to the list (initialization) 

void AddRow(CString text, CString ID);
	
//Retrieve the "hidden column" value of the current selection

CString GetCurrentRowID();
	
//Clear combo box and associated string list

void Clear();

//Remove the current combo box item and associate string list item

void RemoveCurrentRow();

I have commented these functions quite liberally so that you should have no problem extending or modifying them.

This control grew out of the need to port applications written in Microsoft Access to Visual C++. Our Access apps made heavy use of combo boxes with a hidden ID field. Typically a user would select from a list of easy to read text but the app actually requires a index value for database lookup, etc.

The autoselect code was borrowed from Chris Maunder's autoselect example available at another source code site. I made a couple of modifications: I needed the combo to alert the parent window when a valid selection is made not only via mouse but if a user types in a partial string, an autoselect match is made and the user tabs out of the control.

I override the reflected ON_KILLFOCUS message within the control and send a ON_CLOSEUP message to the parent window if the selection is valid. I tried ON_SELENDOK but had many problems with the order of events. As well for some reason Microsoft docs state that it's preferrable to use ON_CLOSEUP.

I also modified Chris' example to watch for the escape key and if pressed while in the edit portion of the combo box will revert the edit box text back to the value it was at when the control first received focus. I did this because Access combo boxes allow you to do that and our clients are used to having this happen. (You would not believe how strongly people can feel about little details like this once they are used to them! <grin>)

The hidden column is a CStringList object. When you look at the code you will see that the visible text in the list box is stored in the list box as normal but also stored as a column in the string list with the ID being a second column in the string list. Why did I do it like this? Because sometimes I want to display a completely different value to the user but still store the original text and ID column. You can easily remove or add more "columns" if you like.

I use this control in dialog and FormView based projects. Developed in Visual studio 6, I'm not certain if it will compile in previous versions or not but it does compile cleanly under warning level 4.

Please email me at john@zerocentral.com if you find a bug, have a suggestion or question.

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My vote of 1 Howard Richards 23:10 29 Jan '09   Java-level UI design Sign In·View Thread·PermaLink combo box code net123 3:05 1 Mar '08   i require the code for accessing one field from the database and displaying it in the combo box.on click and also the steps Sign In·View Thread·PermaLink 1.71/5 (4 votes) Re: combo box code John C 7:27 1 Mar '08   That doesn't sound like anything related to this article, perhaps you should google for an answer or ask in the general forums. When everyone is a hero no one is a hero. Sign In·View Thread·PermaLink 2.00/5 (1 vote) problem help please feritu 0:40 24 Nov '06   I am adding files and changing control name as you said but actually nothing changes in my dialog box combos!!,and also no errors,do you have an idea?Thanks.:( Sign In·View Thread·PermaLink 1.00/5 (1 vote) Re: problem help please feritu 4:18 24 Nov '06   i made a mistake somewhere and i found it thanks for the code Sign In·View Thread·PermaLink 5.00/5 (1 vote) Combo Box in SDI application Aditya Rao 3:05 5 Aug '05   hi    i want to display a combo box in SDI application where the view class is derived from CFormView so that i am able to use the features of a dialog based application but everytime am trying to add a string in the combo box i get an exception when i execute the program. can anyone help me. i have written the code for writing to the combo box in the OnCreate function of the view class. thanks aditya Sign In·View Thread·PermaLink Nope Klaus Probst 14:49 6 Feb '02   I'm sure you are confusing the Access combo with its VB brother. The VB ones have no such functionality, unless XP suddenly bestowed it upon them. But anyways, it's cool ___________ Klaus [www.vbbox.com] Sign In·View Thread·PermaLink Re: Nope J Cardinal 15:03 6 Feb '02   Access-like combo? I've never used VB, I made an assumption that they were the same. Come to think of it, the road to hell is probably paved equally with assumptions as with good intentions. Ground Zero Tech-Works http://www.ayanova.com Sign In·View Thread·PermaLink Searching in the ComboBox by Index Bernhard 23:25 18 Nov '01   Hi.. i am using your ComboBox and it is a big help, but i never used the hidden column. Now i did want to use it, but i have got a single problem: i would like to search for an item in the combo box, but the key would be the index. First i thought that it would be easy.. but now i am stuck (i've never used CStringList and the more i now em the more i hate the MFC - Container Classes): int CgzCombo::SearchRowID (LPCSTR s_ID) { POSITION pos = 0; int i = 0; CString s_back; pos = plist[1]->Find (s_ID); //the problem here is that i should find the index i of the position pos return i; } i hope somebody could help me.. and thanks in advance bernhard ""Politicians and diapers have one thing in common. They should both be changed regularly and for the same reason." Sign In·View Thread·PermaLink Re: Searching in the ComboBox by Index J Cardinal 15:12 6 Feb '02   Sorry, I didn't see your post until just now. It was quite some time ago that I posted this article and I've since added a *lot* of functions to it. Yes stringlists are wierd at first and are quite obviously missing the function that you mentioned. It completely escapes me why they didn't include it, but it gives us something to do. Once they start to make sense though they have many uses, I particularly like CObjectList as well and have found many perfect fits for it. Here is the code that I use to select an item in the combo based on the hidden ID column, it's straight out of an active project so a bit rough but it should give you or anyone else interested the basic idea. ----------- //Select a string in combo based on id value bool CgzCombo::Select(CString ID) { //finds row that matches ID and selects it //as the displayed item //I could not find a simpler way to do this //because stringlist objects dont appear to have // a function that returns and index of a given // item. They do return POSITION types but according // to the docs that is not to be considered an index // value in any way. //this function does not generate an On_closeup message //as the other selection functions do because I use it //for displaying an initial record from a database //and no change has been made to the actual record so I //don't want to process it that way. //assert on an empty ID string if in debug mode _ASSERTE(!ID.IsEmpty()); //handle an empty ID string in release mode if(ID.IsEmpty()) return false; int x; POSITION pos; //if the list is empty, return if(plist[1].IsEmpty()==TRUE) return false; //set x to the number of items in the list x=plist[1].GetCount(); //bail if there is nothing in the list if(x==0) return false; //iterate through the list comparing the id //string at each y index location to the passed ID value //upon a match we know that y is the index value in the //combo box that matches the ID value passed to this function //CHANGE: changed y for(int y=0;y { //will assert if invalid id attempted pos=plist[1].FindIndex(y); _ASSERTE(pos!=NULL); if(pos==NULL) return false; if(ID==plist[1].GetAt(pos)) { SetCurSel(y);//found a match, set the combo to it return true; } } //default to top of list //Added 05/26/00 3.34 pm SetCurSel(0); return false; } -------- Ground Zero Tech-Works http://www.ayanova.com Sign In·View Thread·PermaLink Thank you for your reply.. Bernhard 21:17 10 Feb '02   J Cardinal wrote: Once they start to make sense though they have many uses, I particularly like CObjectList as well and have found many perfect fits for it. exactly the "POSITION" var was the thing that made me sick of the mfc containers and forced me to use the stl - containers.. and after some time messing around with them i have to admit that i like em.. but thanks for your reply... i've tackled the problem and solved it a little bit differently.. and now it works well bernhard Sometimes I think the surest sign for intelligent life elsewhere in the universe is that none of them ever tried to contact us. Sign In·View Thread·PermaLink Setting the Current Item Giles 7:16 26 Sep '01   What do you think the best way is to preselect a particular item? Giles Sign In·View Thread·PermaLink Re: Setting the Current Item BugZ RevengE 15:37 4 Feb '02   just use the .SetCurSel(n) function of the class... because the gzCombo class is is derived from the ComboBox class you can use any function from the ComboBox class in it... so: gzCombo.SetCurSel(0) will select the first object in your combo box gzCombo.SetCurSel(1) will select the second... and so on just dont forget to start your count at 0 not 1... very common in c programming... ----------- Why Me? Sign In·View Thread·PermaLink Re: Setting the Current Item J Cardinal 15:10 6 Feb '02   I think what you might be looking for is in my response to Bernard. I guess I should update this article, we've changed and expanded on it quite a bit since then. - John Ground Zero Tech-Works http://www.ayanova.com Sign In·View Thread·PermaLink Memory Leak!!! Mike Wild 0:43 6 Apr '00   In the d'ctor delete[] pList is missing!!!! Mike Wil Sign In·View Thread·PermaLink Re: Memory Leak!!! JCardinal 6:07 6 Apr '00   Yes it's a big hairy bug! I have sent an update in which replaces the CgzCombo destructor with this: CgzCombo::~CgzCombo() { delete[] plist; } Thanks for spotting that Mike! Sign In·View Thread·PermaLink 2.00/5 (2 votes)

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