RadMultiColumnComboBox: How can I prevent the ComboBox Editor from line breaking/word wrapping?

[ClausDC]

Please consider the attached image.

How can I prevent the editor from line breaking when the selected item in the combobox fills out the whole (or more) width of the combobox editor? I want it to keep the height of a single line and just scroll the text, like in a single line textbox.

[Martin Ivanov]

Hello Claus,

To achieve your requirement, you can replace the default items panel of the control. You can do this using the following approach:

private void RadMultiColumnComboBox_Loaded(object sender, RoutedEventArgs e)
{
	var mccb = (RadMultiColumnComboBox)sender;
	var itemsControl = mccb.FindChildByType<SearchAutoCompleteBoxesItemsControl>();
	itemsControl.ItemsPanel = this.Resources["stackPanelTemplate"] as ItemsPanelTemplate;
}

<Window.Resources>
        <ItemsPanelTemplate x:Key="stackPanelTemplate">
            <StackPanel />
        </ItemsPanelTemplate>
</Window.Resources>

I hope that helps.

Regards,
Martin Ivanov
Progress Telerik

[ClausDC]

Unfortunately, that doesn't work, the editor still gets wrapped. Probably because ultimately, the input box of the control is not a TextBox but an ItemsControl within a ScrollViewer. Even when forcing it in a single line, you still would need horizontal scrollbars which wouldn't fit at all.

It's just too different from a regular ComboBox.

We used regular RadComboBoxes before, which fit neatly into a "line". We wanted to see if we could relpace some with this control but the wrapping somewhat destroys the layout we had so far.

[Martin Ivanov]

You are right. It seems that the custom items control implementation is forcing the height to increase. One way to avoid this is to modify the ControlTemplate of SearchAutoCompleteBox element (part of the MultiColumnComboBox' template).This will allow you to remove the ScrollViewer and set a fixed height to the control. You can find this approach shown in the attached project. I hope it helps. Note that the customized template is based on the default Office_Black theme. To use it for another theme, you should extract the associated template and apply the needed changes. 

[ClausDC]

Actually I kind of found a solution: When setting the "SelectionBoxesVisibility" property to "Collapsed", the behavior of the control is pretty close to the desired behavior.

Unfortunately, the editor textbox (a RadWatermarkTextBox as I understand it after looking at the control templates) doesn't update to the selected item (through DisplayMemberPath), when the SelectedItem is changed through the data binding source. When changing it through the UI by typing or selection in the DropDown, it changes the displayed text correctly however.

It seems I can force it by subscribing to SelectionChanged/Loaded events and retrieving the RadWatermarkTextBox through FindChildByType and then setting the Text manually but this is kind of messy and not very elegant.

It would be nice if the RadWatermarkTextBox reacted to the changes in the data binding source.

[Martin Ivanov]

I've tested this and the textbox is updated correctly when you update the SelectedItem. Can you check the attached project and tell me if I am missing anything?

[ClausDC]

Yeah, I have to correct my initial assumption. It does update, however only when the contol is loaded in the VisualTree.

I was setting SelectedItem via binding before the control was loaded.  It appears that the text of the RadWatermarkTextBox doesn't initially get set. I solved this for now with the method described in my answer above by subscribing only to the Loaded event and setting the text of the RadWatermarkTextBox manually.

After that, it's not necessary to subscribe to SelectionChanged and updating the TextBox manually, like you wrote Martin.

Still, what remains is that the RadWatermarkTextBox should set its Text property to the initial value of SelectedItem, once it is loaded, I think.

[Martin Ivanov]

Thank you for the additional description. It turns out that this is an issue in the control. Basically, the text is updated manually on SelectedItem changed, however, if you set the selection item before the control was loaded, the textbox part is not yet loaded, so its text cannot be assigned. I have logged a new bug report in the Telerik feedback portal where you can track its status. You can also find your Telerik points updated.

To work this around, you can use your approach, or one of the following options. You can use the Loaded event in order to reset the SelectedItem setting of the control.

private void RadMultiColumnComboBox_Loaded(object sender, RoutedEventArgs e)
{
	var mccb = (RadMultiColumnComboBox)sender;            
	var selection = mccb.SelectedItem;
	mccb.SetCurrentValue(RadMultiColumnComboBox.SelectedItemProperty, null);
	mccb.SetCurrentValue(RadMultiColumnComboBox.SelectedItemProperty, selection);
}

Or you can ensure that the SelectedItem property of your view model is set after the InitializeComponent call of the view that hosts the RadMultiColumnComboBox control.