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 Populating As PopulatingEventHandler
<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 Sub AutoCompleteBox_Populating(ByVal sender As Object, ByVal e As PopulatingEventArgs)
        e.Cancel = True
    End Sub

    ' Call the topic service at the live search site. 
    Private wc As WebClient
    Private Sub CallToWebService()
        wc = New WebClient()
        wc.DownloadStringAsync(New Uri("" & _
            myACB.SearchText & "&sources=news"))
        AddHandler wc.DownloadStringCompleted, AddressOf wc_DownloadStringCompleted
    End Sub

    Private Sub wc_DownloadStringCompleted(ByVal sender As Object, _
            ByVal e As DownloadStringCompletedEventArgs)
        If e.[Error] IsNot Nothing Then
            Exit Sub
        End If

        Dim data As New List(Of String)()
            Dim jso As JsonObject = TryCast(DirectCast(JsonObject.Parse(e.Result),  _
                JsonObject)("SearchSuggestion"), JsonObject)
            Dim originalSearchString As String = jso("Query")
            If originalSearchString = myACB.SearchText Then
                For Each suggestion As JsonObject In DirectCast(jso("Section"), JsonArray)

                ' Diplay the AutoCompleteBox drop down with any suggestions 
                myACB.ItemsSource = data
            End If
        End Try
    End Sub
End Class


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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