How to control 2 ComboBoxes with a Custom Event?

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Hi all,
I have two comboboxes like cbCountry and cbCity. I use BindingSource to fill them with a relational way. When cbCountry.SelectedIndex = -1 , cbCity's SelectedIndex property gets to -1 by using KeyDown event. There is no problem for this steps. But, although cbCountry and cbCity's SelectedIndex property = -1, user can select an item on cbCity without selecting any on cbCountry. So, I want to create a custom event to check cbCity's SelectedIndex property like that;

When cbCity's SelectedIndex property changed, the event look at if cbCountry.SelectedIndex = 1 or not. If cbCountry.SelectedIndex = -1, this event makes cbCity's SelectedIndex property -1 as well. Actually I have used a custom event for a combobox, but for this situation I need to use two comboboxes in one event I have to check cbCountry.SelectedIndex and to change cbCity's SelectedIndex property in this event.

So, how can I do that with an event like below that I use to control one Combobox control? At this example that controls only cbCity's KeyDown property and if the key equal to Delete, it makes cbCity's SelectedIndex property -1.

C#

internal void SetSingleComboboxIndex(object sender, KeyEventArgs e)
    {
        if (e.KeyCode == Keys.Delete)
           ((ComboBox)sender).SelectedIndex = -1;
    }


    internal void ClearSingleCombobox(ComboBox cb)
    {
           cb.KeyDown += new System.Windows.Forms.KeyEventHandler(SetSingleComboboxIndex);
    }

Posted 2-Aug-11 22:48pm

H.Johnson

Updated 2-Aug-11 22:55pm

Herman<T>.Instance

v2

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Herman<T>.Instance · Answer 1 · 2011-08-02T22:56:00

Solution 1

you should be able to retrieve the ID of the comboBox in method SetSingleComboboxIndex.

If that ID = cbCountry and the selectedIndex = -1, set cbCity.Enabled to false; else to true;

Posted 2-Aug-11 22:56pm

Herman<T>.Instance

Sergey Alexandrovich Kryukov · Answer 2 · 2011-08-02T23:11:00

The whole idea of "deselecting" seems quite weird to me; I did not really understand its purpose. However, I can see a different problems.

1) If the method ClearSingleCombobox is called repeatedly (as I would assume looking at the name of this method), you are in trouble. In this case every time you "clear", you're adding the same method to the event's invocation list. It can cause a really good memory leak at best.

2) Both methods you show don't have to be instance methods, they can be static as "this" parameter is unused because of cb. For performance reasons, if a method can be static it should be static. For example, Microsoft FxCop (recommended) will not pass this code.

—SA