Question

So I have this little problem making this to work:

1. I have silverlight client app that has custom usercontrol with tri-state checkbox with two-way binding

2. After user changes checkbox value, function underlying the property translates the value to integer:

      -1 nothing
       0 false
       1 true
   

3. After user saves data from dialog box, all data(complex object) is being serializes and sent over to webservice and stored in SQL db.

4. When client requests saved data back from webservice, it get back that object OK

5. When I try to bind that returned deserialized object(EA) back to checkbox like this:

          With cC
              Dim b As New Binding("AllowedTo.Create")
              b.Source = EA
              b.Mode = BindingMode.TwoWay
              .SetBinding(CheckBox.IsCheckedProperty, b)
          End With
   

it only works ok if the values are true or false, but if value is nothing, as the checkbox is tri-state, it should turn to that third state – undefined – with minus sign [-], but it dosent.
It just stays at false state – empty with no check, like it would be false.

What could be the problem?

Sorry for my english, its not my mother language

Answer 1

Don’t use an integer for this, use a Nullable Bool (Bool?). Two way binding works well, it converts:

• Checked == true
• Unchecked == false
• Indeterminate == null

Serialization isn’t a problem with nullable bools, in fact you don’t even have to check if the SQL field value is NULL, since it will be a valid state, and using a bool field in the SQL database will even reduce it’s size a bit 😉

If your database is set, and you can’t change it, write a converter to convert your integer to a nullable bool for the binding, shouldn’t take more then 2 minutes.