ComboBox selection generating list for another comboBox question

mprice214

Hi all, I have the following code I'm trying to get working. When I change the selection in the comboBox in column1, I want the list generated if the selection was "Test1". However, it seems no list is generated. Any help would be appreciated. Thanks.

public class Units
{
public string Unit { get; set; }

    }


    private void column1DataGridViewTextBoxColumn\_SelectedIndexChanged(object sender, DataGridViewCellEventArgs e)
    {

        string strPrimary = column1DataGridViewTextBoxColumn.ToString();
        Debug.WriteLine(strPrimary);
        if (strPrimary == "Test1")
        {

            //Build a list 
            var dataSource = new List<Units>();
            dataSource.Add(new Units() { Unit = "blah1" });
            dataSource.Add(new Units() { Unit = "blah2" });
            dataSource.Add(new Units() { Unit = "blah3" });

            //Setup data binding 
            this.column2DataGridViewTextBoxColumn.DataSource = dataSource;
            this.column2DataGridViewTextBoxColumn.DisplayMember = "Unit";
            
        }
    }

William Winner

Wow...I'm really confused by your code. Is column1 a ComboBox column or a TextBox column? Because you named it column1DataGridView**TextBox**Column. But let's say that it actually is a ComboBox column. What is it that you think column1DataGridViewTextBoxColumn.ToString() does? It creates a string that gives you basic information about the object. So, for instance, I added a ComboBox column to a DataGridView. The ToString() method returns "DataGridViewComboBoxColumn { Name=Column1, Index=0 }". That's what you're checking to see if it equals "Test1". It never will. What you want to be checking is:

string strPrimary = (ComboBox)sender.SelectedText;

I'd say if you don't have this kind of basic understanding as to what these methods do, you really shouldn't be trying to mess with DataGridView's and Lists. Seriously, start out with a basic course on C#.

Henry Minute

Try replacing this line

string strPrimary = column1DataGridViewTextBoxColumn.ToString();

with

string strPrimary = dataGridView1\[e.ColumnIndex, e.RowIndex\].Value.ToString();

What you were getting before was something like "DataGridViewComboBoxColumn{something="ibbledibble"}", rather than "Test1". In other words the DataGridViewComboBoxColumn class ToString, rather than the content ToString

Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.” Why do programmers often confuse Halloween and Christmas? Because 31 Oct = 25 Dec.

William Winner

To add to this, you shouldn't have known that column1DataGridViewTextBoxColumn.ToString() wasn't giving you the right result because right after you made that called, you printed the result to the debugger. That didn't tell you anything? You couldn't tell right away that you weren't getting what you expected and that that was the problem?

mprice214

William, "Wow...I'm really confused by your code. Is column1 a ComboBox column or a TextBox column? Because you named it column1DataGridViewTextBoxColumn" As I'm just trying to get through the mechanics of this, I wasn't worried about changing the names, but rather leaving them as default (as I changed the column type to a comboBox through the IDE). That is noted for the next time I post something.

William Winner wrote:

That didn't tell you anything? You couldn't tell right away that you weren't getting what you expected and that that was the problem?

Yes. It told me that I wasn't doing something correctly. That is why I posted to get some help (sometimes kind and sometimes.....) on this forum. I didn't know where the problem was. I have made it through James Foxall's C# in 24 hours and also tons of internet tutorials. As you noted, I am not an expert and I am trying to do something way to complex for me and unfortunately I get stuck on the simple things. Unfortunately, I cannot afford a C# programmer for this project and have spent many hours away from family. Truth be told, I am a hands-on mechanical engineer trying to write software, which has proven to be painful, but also gratifying when things actually work. Not looking for sympathy here, but some courtesy would be appreciated. However, I do appreciate your suggestions, even though the wrapping wasn't too tasty.

mprice214

Henry Minute wrote:

What you were getting before was something like "DataGridViewComboBoxColumn{something="ibbledibble"}", rather than "Test1". In other words the DataGridViewComboBoxColumn class ToString, rather than the content ToString

I was getting that if I removed the following lines and put them under the form load method.

string strPrimary = column1DataGridViewTextBoxColumn.DisplayIndex.ToString();
Debug.WriteLine(strPrimary);

If I left it under

public void column1DataGridViewTextBoxColumn_SelectedIndexChanged(object sender, DataGridViewCellEventArgs e)

it didn't execute that when I changed the comboBox value. With that said, I understand your suggestion, but the SelectedIndexChanged method isn't being triggered for some reason.

Henry Minute

This is how to get the SelectedIndexChanged event handler hooked up properly. Handle the EditingControlShowing event of your DataGridView. It's rather nifty.

	private void dataGridView1\_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
	{
		ComboBox cb = e.Control as ComboBox;

		if (cb != null)
		{
			// first remove event handler to keep from attaching multiple:
			cb.SelectedIndexChanged -= cb\_SelectedIndexChanged;
			// now attach the event handler
			cb.SelectedIndexChanged += cb\_SelectedIndexChanged;
		}
	}



	void cb\_SelectedIndexChanged(object sender, EventArgs e)
	{
		MessageBox.Show("Selected index changed");
	}

Simply substitute the correct control names/indexes to suit your application. Good luck! :) [Edit] You can refine this slightly to enable handling SelectedIndexChanged events for more than one ComboBoxColumn.

private void dataGridView1\_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
   ComboBox cb;

   switch (dataGrid.CurrentCell.ColumnIndex)
   {
       case 0:  // use the index for your comboboxcolumn
           cb = e.Control as ComboBox;
           if (cb != null)
           {
           // first remove event handler to keep from attaching multiple:
           cb.SelectedIndexChanged -= cb\_SelectedIndexChanged;
           // now attach the event handler
           cb.SelectedIndexChanged += cb\_SelectedIndexChanged;
           }
           break;
      case 3: // use the index for your second combo
           cb = e.Control as ComboBox;
           if (cb != null)
           {
           // first remove event handler to keep from attaching multiple:
           cb.SelectedIndexChanged -= cb\_SecondSelectedIndexChanged;
           // now attach the event handler
           cb.SelectedIndexChanged += cb\_SecondSelectedIndexChanged;
           }
           break;
   }

[/Edit] Hope this helps. :)

Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.” Why do programmers often confuse Halloween and Christmas? Because 31 Oct = 25 Dec.

modified on Tuesday, May 18, 2010 2:53 PM

mprice214 · modified on Tuesday, May 18, 2010 2:53 PM

Check out my picture on my profile. There is a reason I put that picture on there. That is about how I feel at the moment (and others) :| It seems you are instantiating ComboBox cb. I am confused on a couple of things here. If I have already changed a column type to a comboBox via the IDE, how does it tie in here? Should I be using the DataPropertyName under "Data" in the IDE or (Name) under "Design" in the IDE when referring. I have a generic question about binding, but I'll post a new message for that.

William Winner

It would have solved some issues if we knew that you were never getting to the SelectedIndexChanged code. I assumed that you had already handle the EditControlShowing event and added the event handler for the SelectedIndexChanged event. Henry gave you code to do this, but I can try to explain what is happening since you seemed a bit confused about it. When you create the DataGridView, you can specify columns and specify which column within a table or a datasource that that column is linked to. You can also set up what type of control the column is edited with. You can choose a simple TextBox, or you can have other types, for instance the ComboBox type. When the user clicks within a cell, the DataGridView then checks that column to see what type of control to use to allow the user to edit the cell. This is called the EditControl. If the column type was selected to be a ComboBox, then it will use a ComboBox that the DataGridView created to allow the user to edit the value. It creates the control once and then re-uses it. The EditControlShowing event is set off when the control is actually shown. This ComboBox is just a standard ComboBox and has all of the same events and properties as a standard ComboBox. One of the arguments passed during this event is e.Control. This is the control that is being used. It won't always be a ComboBox...it will be whatever type of control that is being used for that column. So, when that control is passed, you then need to add a handler to whichever event you are interested in...in this case, the SelectedIndexChanged event. You also want to make sure to remove the handler afterwards so that it doesn't get called more than once. In Henry's case, he removed it before adding a new one which is perfectly reasonable since the user could change the selection more than once without the EditControl changing. This may be a bit rambly, but I hope it helps with your understanding of what's happening. I wish you luck with this, but I'm still going to say that an internet course without feedback and online tutorials isn't going to get you far. Your company may not be able to afford a programmer, and it may not fit the timetable for this particular project, but I would suggest finding an entry level course on programming at your community college or state university. You can generally do that pretty cheaply and having an instructor that you can ask questions of can help a ton.

Henry Minute

OK I have looked at your picture and I have to say that I am surprised that you can even reach the keyboard, still let's press on. The

ComboBox cb = e.Control as ComboBox;

line is not instantiating a new ComboBox, it is declaring a variable of the ComboBox type (on the left hand side of the '=') and making it reference (point to) the ComboBox in the cell that you are currently editing. The event that is being handled is the EditingControlShowing event and the DataGridViewEditingControlShowingEventArgs passed to it contain a reference to the editing control being used (e.Control). Because the column we are talking about is a DataGridViewComboBoxColumn, when you start to edit one of its cells, the DataGridView control pops up a real live ComboBox for you to do the edit with (hence the as ComboBox part). (If it were a DataGridViewTextBoxColumn the DGV would give you a TextBox or if it was a DataGridViewCheckBoxColumn the DGV would give you a CheckBox.) So the line is saying to the compiler "Please reserve enough space to hold a reference to a ComboBox which I'll be calling 'cb' and put a copy of the pointer from e.Control in there. Thank you!" (please note that it is a very polite line). Basically it just makes it easier to refer to cb.SelectedIndexChanged for example, rather than:

	private void dataGridView1\_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
	{
		if ((ComboBox)e.Control != null)
		{
			// first remove event handler to keep from attaching multiple:
			((ComboBox)e.Control).SelectedIndexChanged -= cb\_SelectedIndexChanged;
			// now attach the event handler
			((ComboBox)e.Control).SelectedIndexChanged += cb\_SelectedIndexChanged;
		}
	}

which we would have to do otherwise. I hope that you'll agree that the first version is easier to read than this one. If it helps, think of cb as being a 'magic' PhotoCopy of the ComboBox from the cell you are editing. It is magic because any thing you do to the copy also happens to the original. So when the code says to hook up column1DataGridViewTextBoxColumn_SelectedIndexChanged to the copy it is also hooking it up to the real one in your DataGridView When dataGridView1_EditingControlShowing ends, cb is thrown

mprice214

Crystal clear. I appreciate you taking the time. Maybe we could trade CAD work for software. :-D

mprice214

Thanks William. I always knew you software guys have big hearts. I have three small children and I think my wife might go crazy if I do that now, but it may be worth the risk... :laugh: I suggested to Henry that I should trade CAD work for software..... :laugh: Anyway, I'll be working on this later and will let you know how it goes, but both you and Henry have made things very clear.

mprice214

Almost there.....maybe. I'm having object type issues: I've cleaned things up and have the following:

private void column1DataGridViewComboBox_SelectedIndexChanged(object sender, DataGridViewCellEventArgs e)
{

        string strPrimary = dataGridView1\[e.ColumnIndex, e.RowIndex\].Value.ToString();
        Debug.WriteLine(strPrimary);
        if (strPrimary == "Test1")
        {

            //Build a list 
            var dataSource = new List<Units>();
            dataSource.Add(new Units() { Unit = "blah1" });
            dataSource.Add(new Units() { Unit = "blah2" });
            dataSource.Add(new Units() { Unit = "blah3" });

            //Setup data binding 
            this.column2DataGridViewComboBox.DataSource = dataSource;
            this.column2DataGridViewComboBox.DisplayMember = "Unit";

        }
    }



    private void dataGridView1\_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
    {
        ComboBox cb = e.Control as ComboBox;

        if (cb != null)
        {
            // first remove event handler to keep from attaching multiple:
            cb.SelectedIndexChanged -= column1DataGridViewComboBox\_SelectedIndexChanged;
            // now attach the event handler
            cb.SelectedIndexChanged += column1DataGridViewComboBox\_SelectedIndexChanged;
        }
    }

I get "No overload for 'column1DataGridViewComboBox_SelectedIndexChanged' matches delegate 'System.EventHandler'" However, as you probably know, I can change

private void column1DataGridViewComboBox_SelectedIndexChanged(object sender, DataGridViewCellEventArgs e)

to

private void column1DataGridViewComboBox_SelectedIndexChanged(object sender, EventArgs e)

which fixes that. But I need the DataGridViewCellEventArgs class to access the ColumnIndex and RowIndex properties. Thoughts?

Henry Minute

For the SelectedIndexChanged handler, you don't need the Column and Row because each time the handler gets called it is called by the relevant ComboBox. Therefore you can get at the ComboBox by Casting the sender parameter. Here we go again. :-D

private void column1DataGridViewComboBox\_SelectedIndexChanged(object sender, EventArgs e)
{
    ComboBox cb = sender as ComboBox;
    string someString = cb.SelectedItem;
    // OR
    int cbIndex = cb.SelectedIndex;  // and so on
}

or, to do it the longer, more difficult to read way

private void column1DataGridViewComboBox\_SelectedIndexChanged(object sender, EventArgs e)
{
    string someString = ((ComboBox)sender).SelectedItem;
    // OR
    int cbIndex = ((ComboBox)sender).SelectedIndex;  // and so on
}

Good luck! :)

Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.” Why do programmers often confuse Halloween and Christmas? Because 31 Oct = 25 Dec.

mprice214

Wait, let me take my earplugs out....Oh yes, now I think I can see :-D

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
ComboBox cb = e.Control as ComboBox;
if (cb != null)
{
// first remove event handler to keep from attaching multiple:
cb.SelectedIndexChanged -= column1DataGridViewComboBox_SelectedIndexChanged;
// now attach the event handler
cb.SelectedIndexChanged += column1DataGridViewComboBox_SelectedIndexChanged;
}

Since DataGridViewEditingControlShowingEventArgs is handling the EditingControlShowing event and will be passing the arguments to the SelectedIndexChanged event handle, the SelectedIndexChanged event cannot have a handling class that is trying to control the same thing at the same time (in this case the ComboBox). Do you concur?

Henry Minute

mprice214 wrote:

Since DataGridViewEditingControlShowingEventArgs is handling the EditingControlShowing event and will be passing the arguments to the SelectedIndexChanged event handle

I think that you have slightly misunderstood what is happening here. The EditingControlShowing handler does not pass any arguments, it simply tells the ComboBox where to find the code to execute when its SelectedIndex changes and regardless of whatever else is going on it will fire off that code when the index does change. Of course it may not execute it instantly, not even modern computers can really do more than one thing at a time. It has just occurred to me that you are actually asking about the '-=' and '+=' bits. They are like that because the SelectedIndexChanged contains a list of methods that it should execute. If we used the '+=' line only, then each time we did so another instance of the column1DataGridViewComboBox_SelectedIndexChanged would be added to the list meaning that it would execute once after the first time, twice after the second, three times...... You get the idea. So we first '-=' it to remove the handler from the list, before adding it again. Of course we could test to see if it was there already NOTE** this is not real code

if (!cb.SelectedIndexChanged.List.Contains(column1DataGridViewComboBox_SelectedIndexChanged))
{
cb.SelectedIndexChanged += column1DataGridViewComboBox_SelectedIndexChanged;
}

oops forgot to close the tag. but the '-=' then '+=' method is quicker. Hope that this helps. :)

Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.” Why do programmers often confuse Halloween and Christmas? Because 31 Oct = 25 Dec.

modified on Wednesday, May 19, 2010 10:31 AM

mprice214 · modified on Wednesday, May 19, 2010 10:31 AM

Henry Minute wrote:

I think that you have slightly misunderstood what is happening here.

That's a surprise. :^) Got it, but also SelectedIndexChanged cannot access the control via DataGridViewCellEventArgs because the control is accessed via EditingControlShowing with the DataGridViewEditingControlShowingEventArgs class, correct?

Henry Minute

Ah now I understand.

mprice214 wrote:

also SelectedIndexChanged cannot access the control via DataGridViewCellEventArgs because the control is accessed via EditingControlShowing with the DataGridViewEditingControlShowingEventArgs class, correct?

No, that is not quite right. The reason is that each event handler has its own, internally defined, set of parameters, that you have to adhere to. Most event handlers have the object sender (in fact I can't think of one off the top of my head that doesn't) after that most also have some form of EventArgs and if the internal definition says it has to have a plain old EventArgs, then it will only work with EventArgs. If the definition says it should have an DataGridViewCellEventArgs then it will only work if you declare it with one of those. SelectedIndexChanged has an EventArgs because it doesn't need to pass any additional information. You know who sent it from the sender parameter. The fact that the event has fired means that the SelectedIndex of the sender has changed and that is all the information you need to make use of it DataGridViewEditingControlShowingEventArgs holds additional information about where in the DataGridView (Column, Row) the event was fired from.

Henry Minute Do not read medical books! You could die of a misprint. - Mark Twain Girl: (staring) "Why do you need an icy cucumber?" “I want to report a fraud. The government is lying to us all.” Why do programmers often confuse Halloween and Christmas? Because 31 Oct = 25 Dec.

mprice214

I understand. As I continue, I'm sure it will more embedded.

mprice214

Guess who. I have the following:

private void column1DataGridViewComboBox_SelectedIndexChanged(object sender, EventArgs e)
{

        ComboBox cb = sender as ComboBox;

     
        string strPrimary = cb.SelectedItem.ToString();
        Debug.WriteLine(strPrimary);

        var dataSource = new List<Units>();

        switch (strPrimary)
        {
            case "1":
                
            //Build a list 
            
            dataSource.Add(new Units() { Unit = "blah1" });
            dataSource.Add(new Units() { Unit = "blah2" });
            dataSource.Add(new Units() { Unit = "blah3" });

            //Setup data binding 
            this.column2DataGridViewComboBox.DataSource = dataSource;
            this.column2DataGridViewComboBox.DisplayMember = "Unit";

            break;

            case "2":

            //Build a list 
            dataSource.Add(new Units() { Unit = "blah4" });
            dataSource.Add(new Units() { Unit = "blah5" });
            dataSource.Add(new Units() { Unit = "blah6" });

            //Setup data binding 
            this.column2DataGridViewComboBox.DataSource = dataSource;
            this.column2DataGridViewComboBox.DisplayMember = "Unit";

            break;

            case "3":

            //Build a list 
            dataSource.Add(new Units() { Unit = "blah7" });
            dataSource.Add(new Units() { Unit = "blah8" });
            dataSource.Add(new Units() { Unit = "blah9" });

            //Setup data binding 
            this.column2DataGridViewComboBox.DataSource = dataSource;
            this.column2DataGridViewComboBox.DisplayMember = "Unit";

            break;

        }
    }

Well, the problem of course as you know is that ComboBox cb points to the second comboBox once I select it. In fact, once I select a value on the first comboBox and then select the second comboBox to select a value, debug.writeline gives me "WindowsFormsApplication1.Form1+Units" (although the 2nd comboBox does get populated with the appropriate list based upon the selection of the first comboBox). If I use an integer instead of strPrimary and set it as cb.SelectedIndex, what I actually get from debug is the index of the selection of the list of the second comboBox (eg if blah5 is selected, I get an integer = 1) followed by an integer