Question

I’m attempting to convert the displayed value of a combobox by using its binding as a key to look for the value I would like to display. I can’t seem to get it to work.

The datacontext of my user control is MyObject.
MyObject has a property “MasterDrawerId”, which is the Id of “MyReferencedObject”.

Elsewhere in my application, accessible through a static property of my App.xaml.cs is a collection of “MyOtherObjects”. “MyReferencedObject” has a foreign key relationship with the Id of “MyOtherObject”.

My combobox is bound to the “MasterDrawerId”, which is what’s passed into the converter.
I then use that as a lookup for “MyReferencedObject” to get the foreign key Id of “MyOtherObject” in order to display the name of that object.

I know it seems confusing but it’s basically just using the property of the datacontext in order to do a lookup and display the name of another object in its place within a combobox.

This is my code:

masterSiteComboBox.DisplayMemberPath = "Name";
Binding binding = new Binding("MasterDrawerId");
binding.Mode = BindingMode.TwoWay;
binding.Converter = new DrwIdToSiteConverter();
masterSiteComboBox.SelectedItem = binding;
masterSiteComboBox.ItemsSource = ListOfMyOtherObjects;

Here is my converter code:

public class DrwIdToSiteConverter : IValueConverter
{
public DrwIdToSiteConverter()
{
}

    public virtual object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        XferSite site = new XferSite();

        foreach(XferUserDrawerPermissions perm in App.UserDrawerPermissions)
        {
            if (perm.DocumentTypeId.Match(value.ToString()))
            {
                site.Id = int.Parse(perm.SiteId);
                site.Name = perm.SiteName;
                break;
            }
        }

        return site;
    }

    public virtual object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value;
    }
}

I set a breakpoint at the first line of my “Convert” method of my converter and it never gets hit.

Answer 1

Instead of

masterSiteComboBox.SelectedItem = binding;

do

masterSiteComboBox.SetBinding(ComboBox.SelectedItemProperty, binding);