C# Discussion Boards - CodeProject

9-Jul-07 21:36

Hello all,

I have a form and a few comboboxes in it. When the user drops down a combobox and selects a different item, I wish to execute a piece of code, which involves a alot of database transactions. I am handling the SelectedIndexChanged(object sender, EventArgs e) event of the combobox. But this method gets called even if the user has selected the same item, which was previously selected. Am I handling the wrong event or is there anything more I need to do?

Nobody can give you wiser advice than yourself. - Cicero

Muhammad Gouda9-Jul-07 21:49

Muhammad Gouda

9-Jul-07 21:49

brahmma wrote:
Am I handling the wrong event

Ofcourse, you are handling the right event.
All you need is a simple if statement block like this

if(comb.SelectedIndex !== currentSelection)
{
/// All your code goes here
/// Where currentSelection is a user defined variable which must be
/// member of your Form class
}

Does this help

Mohamed Gouda
Egypt

Rajesh R Subramanian9-Jul-07 21:53

9-Jul-07 21:53

Hello there,

Thank you very much for your inputs. I don't get it. Isn't the handler supposed to check it? The name of the handler is SelectedIndexChanged and why in the hell should I check if it is changed or not? Why does this event handler even exist? Shouldn't this event be triggered only when the selected index of the particular combobox is changed? Oh crap! Is this the way C# works? I think I am going back to MFC.

Nobody can give you wiser advice than yourself. - Cicero

Urs Enzler9-Jul-07 22:38

Urs Enzler

9-Jul-07 22:38

Unfortunately, there are a lot of PropertyChanged events in C# that are fired whenever a value is set whether a the value really changed or not.

And it is very annoying!

But going back to MFC isn't really an option for me Smile | :)

-^-^-^-^-^-
no risk no funk

Rajesh R Subramanian9-Jul-07 23:34

9-Jul-07 23:34

Urs Enzler wrote:
Unfortunately, there are a lot of PropertyChanged events in C# that are fired whenever a value is set whether a the value really changed or not.

And it is very annoying!

I'm annoyed too! But, I think I must get used to it rather than bitching about it Smile | :)

Nobody can give you wiser advice than yourself. - Cicero

Rajesh R Subramanian9-Jul-07 23:43

9-Jul-07 23:43

Mohammed Gouda wrote:
if(comb.SelectedIndex !== currentSelection)

What is that currentSelection here? Am I supposed to maintain a static variable where I store this information?

Nobody can give you wiser advice than yourself. - Cicero

Muhammad Gouda10-Jul-07 0:45

Muhammad Gouda

10-Jul-07 0:45

brahmma wrote:
Am I supposed to maintain a static variable where I store this information?

Yes, that is what I mean

Mohamed Gouda
Egypt

Rajesh R Subramanian10-Jul-07 0:52

10-Jul-07 0:52

Then why do we have an OnSelectedIndexChanged event handler? Doesn't that suck?

Nobody can give you wiser advice than yourself. - Cicero

Martin#9-Jul-07 21:55

9-Jul-07 21:55

Hello,

You are write!
Also the SelectedValueChanged has this behavior. It doesn't check for current setting! Frown | :(

Maybe the TextChanged helps you here. (I know that it could be multible text in the Items!)

All the best,

Martin

Rajesh R Subramanian9-Jul-07 22:00

9-Jul-07 22:00

Martin# wrote:
Maybe the TextChanged helps you here.

No, that has the same behavior too.

Nobody can give you wiser advice than yourself. - Cicero

Martin#9-Jul-07 22:02

9-Jul-07 22:02

brahmma wrote:
No, that has the same behavior too.

Really?
I just tested it!
Selected same Item and event was not fired.

All the best,

Martin

Rajesh R Subramanian9-Jul-07 22:08

9-Jul-07 22:08

Thanks for pointing it out. I had two projects open, and got confused between both. But I think I may run into trouble, because the combobox item text might be changed dynamically depending on a table updation in the database. Somehow, this problem is fixed for now. Thanks a bunch again.

Nobody can give you wiser advice than yourself. - Cicero

Rajesh R Subramanian9-Jul-07 23:45

9-Jul-07 23:45

Martin# wrote:
I know that it could be multible text in the Items!

Exactly! What can I do in case I have multiple items with the same text in the ComboBox? Hmmm | :|

Nobody can give you wiser advice than yourself. - Cicero

Martin#9-Jul-07 23:56

9-Jul-07 23:56

Hello,

brahmma wrote:
What can I do in case I have multiple items with the same text in the ComboBox?

The question is what do you want it to do.

All the best,

Martin

Rajesh R Subramanian10-Jul-07 0:00

10-Jul-07 0:00

Hmm... I want to execute a piece of code whenever the user changes his selection in a combobox. But the TextChanged handler may not work if I have duplicate items in the combobox. And the SelectedIndexChanged will be called even if the user selects the same item again, which sucks. So, do I need to check manually if the user has selected a different item every time and then execute my code? If yes, then why do we have event handlers?

Nobody can give you wiser advice than yourself. - Cicero

Martin#10-Jul-07 0:19

10-Jul-07 0:19

Hello,

brahmma wrote:
And the SelectedIndexChanged will be called even if the user selects the same item again, which sucks

So true!

brahmma wrote:
So, do I need to check manually if the user has selected a different item every time and then execute my code?

I think in your special case, yes!

brahmma wrote:
If yes, then why do we have event handlers?

I guess this statetment comes out of frustration.

An other possibility is, you do what MS was not willed todo:
inherit your own combobox, like this:

public class SpecialComboBox : System.Windows.Forms.ComboBox
{
    private bool init = true;
    private int oldIndex = 0;

    public SpecialComboBox()
    {
    }

    protected override void OnSelectedIndexChanged(EventArgs e)
    {
        if((oldIndex!=this.SelectedIndex)|| init)
        {
            init=false;
            oldIndex = SelectedIndex;

            base.OnSelectedIndexChanged (e);
        }
    }
}

This should do it!

All the best,

Martin

Muhammad Gouda10-Jul-07 0:51

Muhammad Gouda

10-Jul-07 0:51

Very good idea to create your own control that enhances performance of the vendor. I will vote 5 for your message Martin.
My greetings Smile | :)

Mohamed Gouda
Egypt

Martin#10-Jul-07 1:13

10-Jul-07 1:13

Thank you!

All the best,

Martin

Rajesh R Subramanian10-Jul-07 0:51

Re: Problem with SelectedIndexChanged method [modified]

10-Jul-07 0:51

Imagine an ERP package under development with some 300 forms (to which I have access). There are 500+ combo boxes. Now, I have to inherit my own combobox and then... Thanks, Microsoft. Hmmm | :|

Nobody can give you wiser advice than yourself. - Cicero

Martin#10-Jul-07 1:12