WPF ComboBox DropDown Placement

Question

I have a ContentControl comprised from left to right of a Button, partition and a ComboBox. I want the ComboBox dropdown to line up with the left side of the control as opp

Answer 1

I've done something similar before - I ended up deriving from ComboBox, getting the popup part of the control and using the CustomPopupPlacementCallback to position it. Something like this...

class MyComboBox : ComboBox
{
    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        var popup = (Popup)Template.FindName("PART_Popup", this);
        popup.Placement = PlacementMode.Custom;
        popup.CustomPopupPlacementCallback = placePopup;
    }

    private CustomPopupPlacement[] placePopup(Size popupSize, Size targetSize, Point offset)
    {
        var placements = new[] { new CustomPopupPlacement() };
        placements[0].Point = // position the drop-down here!
        return placements;
    }
}