Combobox selectionchanged event triggers without even changing the selection in the ComboBox

Question

Could you help me find the error in this one: The event triggers before even the windows form is loaded. I start to see the message Box and then I click OK,after that it loads the main screen.After that everything works perfectly, I wonder what triggers the ComboBox SelectionChanged Event before even loading the window.The FillComboBoxFamilyData(SegmentCode) just creates a dataset and puts the values int he ComboBox. Please Refer to this link for complete code.

Not able to make cascading comboboxes work

Any help would be highly appreciated.Thanks.

 <ComboBox Height="23" HorizontalAlignment="Left" Margin="35,26,0,0" Name="comboBox1" VerticalAlignment="Top" Width="205" ItemsSource="{Binding Source={StaticResource tblSegmentViewSource}}"  DisplayMemberPath="Segment Name" SelectedValuePath="Segment Code" SelectionChanged="comboBox1_SelectionChanged"/>
 <ComboBox Margin="304,26,395,93" Name="comboBox2" />


    private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

        MessageBox.Show(comboBox1.SelectedValue.ToString());
        SegmentCode = Convert.ToInt32(comboBox1.SelectedValue.ToString());
        FillComboBoxFamilyData(SegmentCode);

    }

Answer 1

At the moment the data will be loaded (attached by the binding), SelectionChanged will be fired. Therefore, you have to check in your event-handler if your app is ready and all the data is loaded and attached. If not, return the event-handler without doing anything. This behaviour is by design.

ItemsSource="{Binding Source={StaticResource tblSegmentViewSource}}"  

You can use the IsLoaded-property to detect, if the binding already has been evaluated. IsLoaded will not be true unless the databinding-engine has evaluated your xaml-bindings.

private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)     { 
   if(!IsLoaded){
      return;
   }
   .... your code here

Answer 2

You can add the following code to make select-change work when the drop-down list is expanded

       if (sender is ComboBox comboBox)
        {
            if (comboBox.IsDropDownOpen)
            {
                var comboBoxSelectedItem = comboBox.SelectedItem;
            }
        }

Answer 3

You can use IsLoaded property of the combo box to test whether it is loaded yet. This is the cleanest and easiest solution which I could find:

var comboBox = (ComboBox)sender;
if (!comboBox.IsLoaded)
{
    // This is when the combo box is not loaded yet and the event is called.
    return;
}

Answer 4

I had this same problem and I found out that setting the starting-selection-index of the combox using xaml will trigger the selectionchanged event when program is loading which causes the error.

To solve you can either set the selection-index to -1 (the default) OR change the current-selection-index of the combobox using code after the program has loaded.

Answer 5

I know this is an old question but I came across it twice trying to fix this in my project and had the same results as the OP. My list is populated after the IsLoaded is true. So, I figured I would post what I figured out for others. Just use the DropDowOpened event to set a bool to true. This way the SelectionChanged event won't fire until the user actually clicks on the dropdown.

private bool UserSeriesChange;
private void comboBox1_DropDownOpened(object sender, EventArgs e)
{
        UserSeriesChange = true;    
}

private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{ 
   if(!UserSeriesChange){
      return;
   }
   .... your code here