ComboBox SelectedIndexChanged event: how to get the previously selected index?

Question

I have a user control which has a ComboBox and a SelectedIndexChanged event handler. In the event handler, I need to be able to tell what was the previously selected index.

Answer 1

I had a similar issue to this in which I set all my combo boxes to "autocomplete" using

ComboBox.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
ComboBox.AutoCompleteSource = AutoCompleteSource.ListItems;

I looped through and set all their lostFocus Events:

foreach(Control control in this.Controls)
{
    if(control is ComboBox)
   {
        ((ComboBox)control).LostFocus += ComboBox_LostFocus;
   }
}

and had a dictionary object to hold old values

public Dictionary comboBoxOldValues = new Dictionary();

then finally ensure the value exists or set to old index, then save to the dictionary

private void ComboBox_LostFocus(object sender, EventArgs e)
{
    ComboBox comboBox = (ComboBox)sender;

    if (comboBox.DataSource is List)
    {
        if (((List)comboBox.DataSource).Count(x => x.YourValueMember == (YourValueMemberType)comboBox.SelectedValue) == 0)
        {
            if (comboBoxOldValues.Keys.Count(x => x == comboBox.Name) > 0)
            {
                comboBox.SelectedIndex = comboBoxOldValues[comboBox.Name];
            }
            else
                comboBox.SelectedIndex = -1;
        }
    }            

    if (comboBoxOldValues.Keys.Count(x => x == comboBox.Name) > 0)
    {
        comboBoxOldValues[comboBox.Name] = comboBox.SelectedIndex;
    }
    else
        comboBoxOldValues.Add(comboBox.Name,  comboBox.SelectedIndex);

    if (comboBox.SelectedIndex == -1)
        comboBox.Text = string.Empty;
}