SelectedValueChanged fires even when the value is not changed?

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I have a combobox with the event SelectedValueChanged associated with a method. I have found how odd it works when I select the old value (the value displayed as its Text property). It raises the event and calls the method!

I'm using a combobox with DropDownStyle = DropDownList, AutoCompleteMode = SuggestAppend and AutoCompleteSource = ListItems. How do I prevent this from happening? I don't want it that way!

It doesn't seem to conform to the name of the event "SelectedValueChanged" that means if the selected value doesn't change, nothing will happen! Thank you so much!

Posted 9-Apr-11 10:45am

King Boy

Updated 9-Apr-11 14:45pm

Nish Nishant

v3

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Sergey Alexandrovich Kryukov 9-Apr-11 20:31pm

Tag it: WPF, WinForms, what?
--SA

Nish Nishant 9-Apr-11 20:45pm

Pretty sure he means Winforms. I've improved his post to add that tag!

Sergey Alexandrovich Kryukov 9-Apr-11 20:34pm

I never faced any abnormality in such cases.
Make a minimal code to show the problem and post it. Don't post the code of your application. Please make a special demo to focus just on the problem.
--SA

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Nish Nishant · Accepted Answer · 2011-04-09T14:43:00

Solution 1

Yeah, that is standard behavior with the ComboBox (in Winforms). Once you drop down the control, then even if you select the same item that was previously selected, SelectedValueChanged will fire! I reckon you'd have to keep a currentSelectedValue and then compare against that each time it fires.

(Note that it's same for SelectedIndexChanged as well)

[Edit]
---------

Just wanted to add that this assumes you are using a databound combobox. I have not checked this behavior with a non-databound combobox with manually added items.

Posted 9-Apr-11 14:43pm

Nish Nishant

Updated 9-Apr-11 14:48pm

v2

Comments

[no name] 10-Apr-11 0:37am

Thank you! :)

Sergey Alexandrovich Kryukov 10-Apr-11 1:11am

Very good, you explained how it works, all correct, my 5. In my answer, I added motivation of it and a simple practical advice what OP can do about it, please see.
--SA

Wendelius 10-Apr-11 2:01am

Well explained, my 5.

Shahin Khorshidnia 10-Apr-11 2:22am

+5

Michel [mjbohn] 10-Apr-11 4:35am

my 5

Espen Harlinn 10-Apr-11 6:33am

Nice reply, my 5

Henry Minute · Accepted Answer · 2011-04-09T14:46:00

Solution 2

If you read the MSDN page[^] for SelectedValue property you will see that the 'value' it is referring to is the value of the ValueMember property. So it may not actually be the event that you need if you are not using data binding.

This doesn't explain the problems you are seeing, of course but it mat be that you should be using the SelecetedIndexChanged event.

Posted 9-Apr-11 14:46pm

Henry Minute

Comments

[no name] 10-Apr-11 0:39am

Thank you! What a helpful suggestion! I should try it! Thank you so much!

Sergey Alexandrovich Kryukov 10-Apr-11 1:12am

Correct, a 5. I actually explained it and what OP can do about it.
--SA

Wendelius 10-Apr-11 2:01am

Good explanation, my 5

Espen Harlinn 10-Apr-11 6:34am

Nice link, my 5

Sergey Alexandrovich Kryukov · Accepted Answer · 2011-04-09T19:10:00

Solution 3

OK, Nishant explained how it works. I just want to add couple of practical notes.

Actually selection is not fired if you simply move selection of the list box. It is fired when you confirm the selection by Enter or dbl-click, so it actually shown in the edit box part of the combo. It is quite reasonable to fire this event of confirmation, no matter is that new or old value.

You can easily get the effect you need: in the event handler, remember old value and compare new value with the old one. If they are the same — do nothing, exit the handler immediately. As simple as that.

—SA

Posted 9-Apr-11 19:10pm

Sergey Alexandrovich Kryukov

Comments

[no name] 10-Apr-11 1:37am

With my programming skill, I could think of that solution with comparing old value to the new. But I have not only combobox but about dozens of such comboboxes. That means I need a corresponding number of variable or an array to store all old values. It makes me crazy! So I want another solution! I also tried with "SelectedIndexChanged" but it did the same as "SelectedValueChanged"!
I have found that the appropriate solution for me is using "TextChanged". It can really help me!
Thank you!

Sergey Alexandrovich Kryukov 10-Apr-11 1:59am

What's the difference, 1 combo box or 90000? No difference. Do it just once, created a class based on ComboBox, and use you derived class instead of. Big deal!
--SA

[no name] 10-Apr-11 1:42am

Oh no, it only helps me when changing to new value by selecting from dropdown list but when pressing any key (with autocompletemode) it doesn't fire! Maybe I should use it with one of SelectedValueChanged or SelectedIndexChanged!

Sergey Alexandrovich Kryukov 10-Apr-11 2:00am

If you concerned about selected index in first place, handle this event. I don't see what could be a problem...
--SA

Wendelius 10-Apr-11 2:02am

Good addition, my 5

Sergey Alexandrovich Kryukov 10-Apr-11 2:09am

Thank you, Mika.
--SA

[no name] 10-Apr-11 2:53am

Thank you SA! Your suggestion of "creating a new class based on combobox.." is so great!
But as I said, I have my own solution with TextChanged and SelectedValueChanged working together to make what I want. The following code has been tested:
bool valuechanged= false;
private void ontextchanged(object sender, EventArgs e)
{
valuechanged = true;
}
private void onvaluechanged(object sender, EventArgs e)
{
if(!valuechanged) return;
MessageBox.Show("Value change!";
valuechanged = false;
}
It works well without needing to store any old values!
Thank you!

Sergey Alexandrovich Kryukov 10-Apr-11 14:20pm

If fact you still store different field -- value changed, a different variant.
If's fine as soon as it works for you.
Thanks for accepting this Answer.
--SA

Espen Harlinn 10-Apr-11 6:36am

Great reply - showed how to go about creating a nice and simple solution, 5+++

Sergey Alexandrovich Kryukov 10-Apr-11 14:20pm

Thank you, Espen.
--SA