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ComboBox with Dictionary and ClearSelection

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Dario Concilio
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Dario Concilio asked on 27 Sep 2016, 07:39 AM


I'm creating a ComboBox that contains a Dictionary<byte,string> (for ex.) and ClearSelectionbuttonVisibility = Visible.

It's all ok, but if I click on "Clear Selection", it gives me ad error (that I attached).

I had to declare my property SelectedItem as KeyValuePair<byte, string>.

Now, I think that the reason's error is that KeyValuePair<byte,string> is not nullable, then?

How can I do use Dictionary in this context?

<!--My ComboBox for Dictionary-->
<telerik:RadComboBox ItemsSource="{Binding MyItems}"
                     SelectedItem="{Binding SelectedItem,Mode=TwoWay}"
                     Style="{StaticResource FieldLongComboBoxStyle}"/>
<Style x:Key="FieldBaseComboBoxStyle" TargetType="telerik:RadComboBox" BasedOn="{StaticResource RadComboBoxStyle}">
    <Setter Property="Margin" Value="5"/>
    <Setter Property="ClearSelectionButtonVisibility" Value="Visible"/>
    <Setter Property="ClearSelectionButtonContent" Value="Clear selection"/>
    <Setter Property="TextSearchMode" Value="StartsWith"/>
    <Setter Property="EmptyText" Value="Valore non selezionato"/>
    <Setter Property="HorizontalAlignment" Value="Left"/>
        <DataTrigger Binding="{Binding CantUpdateModel}" Value="True">
            <Setter Property="IsReadOnly" Value="True"/>
            <Setter Property="IsEditable" Value="False"/>
            <Setter Property="IsHitTestVisible" Value="False"/>
            <Setter Property="FontWeight" Value="Bold"/>
        <DataTrigger Binding="{Binding CantUpdateModel}" Value="False">
            <Setter Property="IsReadOnly" Value="False"/>
            <Setter Property="IsEditable" Value="True"/>
            <Setter Property="IsHitTestVisible" Value="True"/>
            <Setter Property="FontWeight" Value="Normal"/>

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Telerik team
answered on 29 Sep 2016, 07:24 AM
Hi Dario,

The observed by you behavior is an expected one and could be observed with the native WPF ComboBox as well - if you simply clear the current SelectedItem the validation will be observed. When the selection is cleared the SelectedIndex is set to -1 and the SelectedItem is cleared - as you are binding to KeyValuePair the value cannot be converted as expected and the validation is visualized.

What we could suggest you is to use a converter for changing the cleared null value to a KeyValuePair. Check the attached sample that demonstrates that approach.

Hope this helps.

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Dario Concilio
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