AutoCompleteBox.MinimumPrefixLength Property


Gets or sets the minimum number of characters required to be entered in the text box before the AutoCompleteBox displays possible matches.

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

public int MinimumPrefixLength { get; set; }
<sdk:AutoCompleteBox MinimumPrefixLength="int"/>

Property Value

Type: System.Int32
The minimum number of characters to be entered in the text box before the AutoCompleteBox displays possible matches. The default is 1.

Population of the AutoCompleteBox does not occur until the conditions specified by the MinimumPrefixLength and the MinimumPopulateDelay property values are met. You can use the MinimumPrefixLength property to delay the population request when manually populating the selector control.

If you set MinimumPrefixLength to -1, the AutoCompleteBox will not provide possible matches. There is no maximum value, but setting MinimumPrefixLength to value that is too large will prevent the AutoCompleteBox from providing possible matches as well.

The following code example demonstrates how to use the MinimumPopulateDelay and MinimumPrefixLength properties together with handling the Populating event to 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

    // 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 { }

   <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" />


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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