[ACCEPTED]-How to prevent/cancel a combobox's value change in c#?-combobox

Save the ComboBox's SelectedIndex when to 2 box if first entered, and then restore it's 1 value when you need to cancel the change.

cbx_Example.Enter += cbx_Example_Enter;
cbx_Example.SelectionChangeCommitted += cbx_Example_SelectionChangeCommitted;

...

private int prevExampleIndex = 0;
private void cbx_Example_Enter(object sender, EventArgs e)
{
    prevExampleIndex = cbx_Example.SelectedIndex;
}

private void cbx_Example_SelectionChangeCommitted(object sender, EventArgs e)
{
    // some custom flag to determine Edit mode
    if (mode == FormModes.EDIT) 
    {
        cbx_Example.SelectedIndex = prevExampleIndex;
    }
}

Here is the simplest fix:-

        bool isSelectionHandled = true;

        void CmbBx_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (isSelectionHandled)
            {
                MessageBoxResult result = MessageBox.Show("Do you wish to continue selection change?", this.Title, MessageBoxButton.YesNo, MessageBoxImage.Question);
                if (result == MessageBoxResult.No)
                {
                    ComboBox combo = (ComboBox)sender;
                    isSelectionHandled = false;
                    if (e.RemovedItems.Count > 0)
                        combo.SelectedItem = e.RemovedItems[0];
                    return;
                }
            }
            isSelectionHandled = true;
        }

0

Save the current value on the Enter event. Implement 6 the BeforeValueChange logic in the ValueChanged event, before the actual 5 ValueChanged logic. If the user cancels, set the stored 4 value and don't continue in the method (return).

If 3 you're going to use this system a lot, I'd 2 suggest inheriting ComboBox and implementing 1 your BeforeValuechange event there.

The Validating event can be used for this 1 scenario
http://msdn.microsoft.com/en-us/library/system.windows.forms.control.validating.aspx

You don't get an appropriate event by default. You 2 could cache the previous value and set it 1 back to that if the user wants to cancel.

How about using the Validating / Validated 3 events?
It works well, if the event happening 2 on LostFocus instead of Change is ok with 1 you.

Otherwise, how about

public void Combobox_ValueChanged(object sender, EventArgs e) {
    if (!AskUserIfHeIsSureHeWantsToChangeTheValue())
    {
        // Set previous value
        return;
    }

    // perform rest of onChange code
}

You could use a message filter to intercept clicks and 6 key presses, which would allow you to prevent 5 the combo box's normal behaviour. But I 4 think you'd be better off disabling the 3 combo box when the user makes a change, and 2 require them to either save or revert their 1 changes.

You can't really prevent it, but you can 2 change it back to the old value if certain 1 requirements aren't met:

private SomeObject = selectedSomeObject=null;

private void cbxTemplates_SelectionChangeCommitted(object sender, EventArgs e)
{
  if (!(sender is ComboBox cb)) return;
  if (!(cb.SelectedItem is SomeObject tem)) return;
  if (MessageBox.Show("You sure?", "??.",
        MessageBoxButtons.OKCancel) != DialogResult.OK)
    cb.SelectedItem = selectedSomeObject;
  else
  {
    selectedSomeObject = tem;
  }
}