AutoCompleteBox.Populating Event


Occurs when the AutoCompleteBox is populating the drop-down with possible matches based on the Text property.

Namespace:  System.Windows.Controls
Assembly:  System.Windows.Controls.Input (in System.Windows.Controls.Input.dll)

public event PopulatingEventHandler Populating
<sdk:AutoCompleteBox Populating="eventhandler"/>

If the event is canceled, by setting the PopulatingEventArgs.Cancel property to true, the AutoCompleteBox will not automatically populate the selection adapter contained in the drop-down. In this case, if you want possible matches to appear, you must provide the logic for populating the drop-down.

For example, when you make a call to a Web service or other long-acting process, you typically use the following steps.

For more information about handling events, see Events Overview for Silverlight.

The following code example demonstrates how to handle the Populating event and populate the AutoCompleteBox manually. This code example sets the PopulatingEventArgs.Cancel property to true to stop auto-population and then calls PopulateComplete when the manual population operation is complete. This code example requires a reference to the System.Windows.Controls.Input assembly.

Run this sample

   <StackPanel x:Name="LayoutRoot" Background="White" Orientation="Horizontal">
    <TextBlock Text="News Topic:" HorizontalAlignment="Left"  VerticalAlignment="Center"/>
    <sdk:AutoCompleteBox VerticalAlignment="Center" HorizontalAlignment="Right" Height="30" 
        Width="100" MinimumPopulateDelay="200" MinimumPrefixLength="3" x:Name="myACB" Populating="AutoCompleteBox_Populating" />

    // Handle the Populating event, but cancel it. Make the call to the web service.
    private void AutoCompleteBox_Populating(object sender, PopulatingEventArgs e)
        e.Cancel = true;

    // Call the topic service at the live search site.
    WebClient wc;
    private void CallToWebService()
        wc = new WebClient();
        wc.DownloadStringAsync(new Uri
            ("" + myACB.SearchText +
        wc.DownloadStringCompleted +=
            new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);

    void wc_DownloadStringCompleted(object sender,
        DownloadStringCompletedEventArgs e)
        if (e.Error != null)

        List<string> data = new List<string>();
            JsonObject jso = ((JsonObject)JsonObject.Parse(e.Result))
                ["SearchSuggestion"] as JsonObject;
            string originalSearchString = jso["Query"];
            if (originalSearchString == myACB.SearchText)
                foreach (JsonObject suggestion in (JsonArray)jso["Section"])

                // Diplay the AutoCompleteBox drop down with any suggestions
                myACB.ItemsSource = data;
        catch { }


Supported in: 5, 4, 3

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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