70-502 Microsoft Certification

Now that I have almost completed the Microsoft 70-502 WPF certification book I started trying to schedule the exam at Prometric but 70-502 is not in their list of exams. This was a bit disconcerting considering that the top Google result for "70-502 Certification" is a Microsoft page that in no way suggests this certification has been retired.

After much research I discovered that the 70-502 certificate has been replaced by MCTS (Exam 70-511): Windows Applications Development with Microsoft .NET Framework 4. This is made even more confusing by the fact that the terms "WPF" and "Windows Presentation Foundation" are conspicuously missing from the title of the certification.

I guess their attitude is they don't have to try hard. Accommodating their incompetence is just part of what it takes to get certified.

I ordered the new book from Amazon. I hope they don't retire this certificate before I'm done reading it.

Changing a binding in code

If you have ever tried to modify a binding in code like this DetailsQty.Binding.StringFormat = "0" you have probably seen the following error...

Binding cannot be changed after it has been used

Previously I discovered this problem with styles and the solution there is to create a new style based on the original one, modify it, then assign it back to the UIElement replacing the original one. Not elegant, but it works.

Dim Style As System.Windows.Style
Style = New System.Windows.Style(GetType(TextBox), DetailsQty.EditingElementStyle)
Style.Setters.Add(New Setter(TextBox.TagProperty, "8N"))
DetailsQty.EditingElementStyle = Style

Unfortunately there is no Binding constructor that takes an existing binding object so we are going to have to work harder. The Binding class does have a Clone method but it is private and we would have to use reflection to call it. I don't want to do that. I wrote a Clone method for bindings. It's very simple. The only tricky bit is that Source, RelativeSource and ElementName are mutually exclusive so I only copy them if they have values.

    Public Shared Function CloneBinding(OldBinding As Binding) As Binding
        Dim NewBinding = New Binding
        If OldBinding.Source IsNot Nothing Then NewBinding.Source = OldBinding.Source
        NewBinding.AsyncState = OldBinding.AsyncState
        NewBinding.BindingGroupName = OldBinding.BindingGroupName
        NewBinding.BindsDirectlyToSource = OldBinding.BindsDirectlyToSource
        NewBinding.Converter = OldBinding.Converter
        NewBinding.ConverterCulture = OldBinding.ConverterCulture
        NewBinding.ConverterParameter = OldBinding.ConverterParameter
        If OldBinding.ElementName IsNot Nothing Then NewBinding.ElementName = OldBinding.ElementName
        NewBinding.FallbackValue = OldBinding.FallbackValue
        NewBinding.IsAsync = OldBinding.IsAsync
        NewBinding.Mode = OldBinding.Mode
        NewBinding.NotifyOnSourceUpdated = OldBinding.NotifyOnSourceUpdated
        NewBinding.NotifyOnTargetUpdated = OldBinding.NotifyOnTargetUpdated
        NewBinding.NotifyOnValidationError = OldBinding.NotifyOnValidationError
        NewBinding.Path = OldBinding.Path
        If OldBinding.RelativeSource IsNot Nothing Then NewBinding.RelativeSource = OldBinding.RelativeSource
        NewBinding.StringFormat = OldBinding.StringFormat
        NewBinding.TargetNullValue = OldBinding.TargetNullValue
        NewBinding.UpdateSourceExceptionFilter = OldBinding.UpdateSourceExceptionFilter
        NewBinding.UpdateSourceTrigger = OldBinding.UpdateSourceTrigger
        NewBinding.ValidatesOnDataErrors = OldBinding.ValidatesOnDataErrors
        NewBinding.ValidatesOnExceptions = OldBinding.ValidatesOnExceptions
        NewBinding.XPath = OldBinding.XPath

        Return NewBinding
    End Function

Now changing an active binding in code is much easier. To change the FormatString on a DataGridTextColumn called DetailsQty we would use this code...

Dim Binding As Binding
Binding = CloneBinding(DetailsQty.Binding)
Binding.StringFormat = "0"
DetailsQty.Binding = Binding