XAML Path Is Not Recognized

Question

I am working with a Transactions class:

Public Class Transactions
	....
	Public Property CurrentTransaction As Transaction
	Public Property Details as DataTable
	
End Class

The Details table has a "CategoryID" column. In the wpf for a Transaction I have:

<Window
	....
	<ComboBox
		x:Name="cbxCategories"
		DataContext="CurrentTransaction/Details.DefaultView"
		DisplayMemberPath="Name"
		HorizontalAlignment="Stretch"
		Margin="0,0,5,4"
		SelectedValue="{Binding Path=CategoryID}"
		SelectedValuePath="CategoryID" />
	....
</Window>

This gives a run-time error:

BindingExpression path error: 'CategoryID' property not found on 'object' ....

What is wrong with my binding?

Answer 1

We are currently investigating the issue and will provide an update soon. Thank you for your patience.

Answer 2

Path=CategoryID is being resolved against the current binding source, and that source is not the row/view object that exposes CategoryID.

The main issue is this line:

DataContext="CurrentTransaction/Details.DefaultView"

That sets a literal string, not a binding expression. In WPF, property paths for data binding must be used through a binding, for example Path="propertyName/propertyNameX" when traversing a hierarchy.

Use a real binding for the source, for example:

<ComboBox
    x:Name="cbxCategories"
    DataContext="{Binding CurrentTransaction/Details.DefaultView}"
    DisplayMemberPath="Name"
    HorizontalAlignment="Stretch"
    Margin="0,0,5,4"
    SelectedValue="{Binding CategoryID}"
    SelectedValuePath="CategoryID" />

Key points:

1. CurrentTransaction/Details.DefaultView must be inside {Binding ...}.
2. In WPF binding paths, / is used for source traversal in hierarchical data.
3. SelectedValue="{Binding CategoryID}" only works if the DataContext is an item that actually has a CategoryID property/column.

If the error continues, inspect the actual runtime binding source in Visual Studio:

• Start debugging.
• Open Debug > Windows > XAML Binding Failures.
• Check the Data Context, Binding Path, and Description columns to see what object WPF is using for CategoryID.

That will show whether the ComboBox is bound to the expected row/view object or to some other object that does not contain CategoryID.

---

References:

• PropertyPath XAML Syntax
• XAML data binding diagnostics