Why Isn't My WPF ComboBox's SelectedItem/SelectedValue Binding Updating?

Binding a WPF ComboBox to a Custom List: Troubleshooting

WPF ComboBoxes readily bind to custom lists via Binding objects. However, SelectedItem or SelectedValue bindings sometimes fail to update correctly. This article addresses common causes and solutions.

Problem: ComboBox Binding Doesn't Update

Several factors can prevent your ComboBox binding from updating:

• Incorrect Property Paths: DisplayMemberPath and SelectedValuePath might not accurately reflect your custom list's property names.
• DataContext Issues: The ComboBox or its parent might lack a properly set DataContext pointing to the ViewModel containing your list.
• ViewModel Binding Problems: Problems within the custom list's ViewModel could hinder property updates.

Solutions:

1. Verify Property Paths: Double-check that DisplayMemberPath and SelectedValuePath precisely match your custom list's property names. For instance:

   <code class="language-xml"><ComboBox DisplayMemberPath="Name" ItemsSource="{Binding Path=PhonebookEntries}" SelectedValuePath="PhoneNumber"/></code>

2. Ensure Correct DataContext: Confirm that the DataContext for the ComboBox (or its ancestor) correctly points to the ViewModel holding your custom list.

3. Examine the ViewModel: Thoroughly review your custom list's ViewModel to ensure its properties update correctly. Implement INotifyPropertyChanged to signal UI updates when property values change.

Further Points:

• Use ReadOnlyCollection<T> for the PhonebookEntries property in your ViewModel to avoid potential binding conflicts with CollectionView.
• Alternatively, override the ToString() method in your custom list objects to define the displayed values in the ComboBox dropdown, eliminating the need for DisplayMemberPath.

This approach should resolve most ComboBox binding update issues. Remember to carefully check your property names and DataContext settings.

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