The following error is thrown when the dropdown of the control is opened: Cannot find governing FrameworkElement or FrameworkContentElement for target element. ... ; target element is 'GridViewItemsSourceProvider; target property is 'ItemsSource' (type 'Object')

If the combobox is placed inside a RadGridView, the error is thrown each time the dropdown is opened (after a commit action).

It would be usefull to have a Property on the RadMultiColumnComboBox which represents the inputted searchtext. This Property should be TwoWay-Bindable.

A usecase for it could be to programmatically manipulate the searchtext.
For example setting it to NULL on LostFocus:

private void mccb_LostFocus(object sender, RoutedEventArgs e)
{
    this.mccb.ChildrenOfType<RadWatermarkTextBox>().First().Text = string.Empty;
}

Instead of hacking around with the visualTree etc. one could simply bind the property. This would also be MVVM compliant.

Proposed Name for the Property "SearchText".

The Validation.ErrorTemplate attached property is not set. To workaround this, you can use the following resource.

<ControlTemplate x:Key="ValidationTooltipTemplate">
    <Grid SnapsToDevicePixels="True" VerticalAlignment="Top">
        <Border Background="Transparent" HorizontalAlignment="Right" VerticalAlignment="Top" Width="3" Height="3"/>
        <AdornedElementPlaceholder x:Name="Holder"/>
        <Border BorderBrush="{StaticResource ValidationTooltipOuterBorder}" BorderThickness="1" CornerRadius="{StaticResource ValidationTooltip_CornerRadius}"/>
        <Path Data="M2,1 L6,1 6,5 Z" Fill="{StaticResource ValidationInnerTick}" Width="7" Height="7" HorizontalAlignment="Right" VerticalAlignment="Top"/>
        <Path Data="M0,0 L2,0 7,5 7,7 Z" Fill="{StaticResource ValidationOuterTick}" Width="7" Height="7" HorizontalAlignment="Right" VerticalAlignment="Top"/>
        <ToolTipService.ToolTip>
            <ToolTip x:Name="PART_ToolTip"
                DataContext="{Binding RelativeSource={RelativeSource Mode=Self}, Path=PlacementTarget.DataContext}"
                Template="{StaticResource ErrorTooltipTemplate}"
                Placement="Right"/>
        </ToolTipService.ToolTip>
    </Grid>
</ControlTemplate>

<Style TargetType="telerik:RadMultiColumnComboBox" BasedOn="{StaticResource RadMultiColumnComboBoxStyle}">
    <Setter Property="Validation.ErrorTemplate" Value="{StaticResource ValidationTooltipTemplate}" />
</Style>

If set the AutoCompleteMode property in a Style Setter, and exception is thrown.

To work this around set the property directly on the control.
<telerik:RadMultiColumnComboBox AutoCompleteMode="Search" />

The RadMultiColumnComboBox has a separate keyboard functionality executed when the watermark textbox (the search box) is focused and the dropdown is open. Basically, you can navigate through the rows of the gridview part and select them using the keyboard. 

Currently, this functionality is private. Introduce an API that allows you to customize the keyboard navigation. Consider something similar to the KeyboardCommandProvider of RadGridView.

Hello Telerik,

Exception is thrown after typing in the autocompletebox and selecting an item right after that. 

Thanks in advance.

The event should fire when the DropDownContentManager gets initialized.

To work this around use the InitializeSelectionBridge event. The DropDownContentManager is initialized when this event fires.

the display of the drop-down part of the multicolumncombobox is different from the RAD combo box. There is an extra line between the content of the combo box and the drop-down button in the office 2016 theme at least. This should not be there to be consistent with the other combo boxes.

Stefan

Hello,

when selecting more items and dropdown positioning is down and input filed has fixed width, the dropdown covers the input field.

It should move down to the bottom edge of input field.