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Welcome to the wpf.lazycombobox wiki!

To use this control, add the assembly to your project. In VisualStudio open the designer of your respective XAML file and either drag the control from the panel or add the <u:LazyComboBox DisplayMemberPath="CompanyName" LookupAction="{Binding Filter}" SelectedItem="{Binding SelectedEntry}" /> tag in XAML.

There are multiple modes of operation:

Binding to a list of complex objects

You can use the following XAML code to lazy-load a list of objects: <u:LazyComboBox DisplayMemberPath="CompanyName" LookupAction="{Binding Filter}" SelectedItem="{Binding SelectedEntry}" />. Note that you DON'T have to supply a ItemsSource which minimizes the amount of data to have to eager-load.

DisplayMemberPath defines the property to display when the control does not have input-focus, and also defines the property to search for, when the user starts to type text into the LazyComboBox.

LookupAction defines the method invoked by the LazyComboBox to populate the list, when the user starts typing or opens the dropdown. See below for details.

SelectedItem is bound 2-way and initially gets the currently selected value. The LazyComboBox will use the DisplayMemberPath (or a fallback to DisplayColumnAttribute of the value's Type, then ToString()) to extract the display-text to show.

Binding to text, where the user can choose from a predefined text, or enter his own

The XAML code <u:LazyComboBox Text="{Binding TextEntry}" ItemsSource="{Binding TextEntries}" /> binds to a static list of texts, and supplies the entered or chosen text via the Text property. Alternatively to supplying a static ItemsSource, you could also use LookupAction, as above.

Binding to a property of a complex object

The XAML code <u:LazyComboBox DisplayMemberPath="DisplayName" SelectedValuePath="Id" IsEditable="False" SelectedValue="{Binding Gender}" ItemsSource="{Binding GenderTypes}" /> for example will take a specific property of the currently selected item (SelectedItem) and extract it's value (based on SelectedValuePath) to SelectedValue. If you assign SelectedValue a new value, LazyComboBox will try to locate the corresponding list-entry by checking the SelectedValuePath of each entry, until it's value matches the SelectedValue.

The LookupAction

Specify a property in your ViewModel: public Action<LookupContext> Filter { get; }. Create the delegate method and assign it to filter in your ViewModel's ctor.

The delegate has the following signature void OnFilter(LookupContext ctx). The passed LookupContext holds the information required for your implementation to fetch the corresponding records. Please note that this action usually will NOT run in the UI thread! You should also check for the supplied CancellationToken to abort any running lookup. Cancellation will be invoked, when the user refines his search-phrase.

FAQ

How can I block the user from being able to enter text?

Set the IsEditable property to False

SelectedItem is reset to NULL, when the dropdown is opened

this occurs if the LazyComboBox cannot find (by using .Equals()) a match within the ItemsSource (either assigned directly or supplied by the LookupAction). Make sure you have overwritten .Equals() in your class.