Change ComboBox Popup border colour

Question

I would like to be able to change the ComboBox Popup border colour without having to override the whole template is there a simple clean way to achieve this.

Thank you for any assistance.

Answer 1

You could refer to the method below to see if it is what you need.
Xaml:

 <Grid>  
        <ComboBox Name="cb" Loaded="cb_Loaded" Height="50" Width="100" >  
            <ComboBoxItem>Item1</ComboBoxItem>  
            <ComboBoxItem>Item2</ComboBoxItem>  
            <ComboBoxItem>Item3</ComboBoxItem>  
        </ComboBox>  
    </Grid>  

Codebehind:

 private T FindVisualChildByName<T>(DependencyObject parent, string name) where T : DependencyObject  
        {  
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)  
            {  
                var child = VisualTreeHelper.GetChild(parent, i);  
                string controlName = child.GetValue(Control.NameProperty) as string;  
                if (controlName == name)  
                {  
                    return child as T;  
                }  
                else  
                {  
                    T result = FindVisualChildByName<T>(child, name);  
                    if (result != null)  
                        return result;  
                }  
            }  
            return null;  
        }  

        private void cb_Loaded(object sender, RoutedEventArgs e)  
        {  

            Popup popup = FindVisualChildByName<Popup>((sender as DependencyObject), "PART_Popup");  
            Border border = FindVisualChildByName<Border>(popup.Child, "DropDownBorder");  
            border.BorderBrush = Brushes.Red;  
        }  

The result:

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