Is it possible to get a popup to ignore MenuDropAlignment in a WPF / Touch app?

I wrote a custom popup that solve this problem: you can set the ForceAlignment dependency property and open it with the "Open" method, or you can directly call "OpenLeft" and "OpenRight" methods.

Public Class CustomPopupInherits Primitives.PopupPrivate Shared moFI As Reflection.FieldInfo = GetType(SystemParameters).GetField("_menuDropAlignment", Reflection.BindingFlags.NonPublic + Reflection.BindingFlags.Static)Public Enum enuForceAlignment    None = 0    Left    RightEnd EnumPublic Property ForceAlignment As enuForceAlignment    Get        Return GetValue(ForceAlignmentProperty)    End Get    Set(ByVal value As enuForceAlignment)        SetValue(ForceAlignmentProperty, value)    End SetEnd PropertyPublic Shared ReadOnly ForceAlignmentProperty As DependencyProperty = _                       DependencyProperty.Register("ForceAlignment", _                       GetType(enuForceAlignment), GetType(CustomPopup), _                       New FrameworkPropertyMetadata(enuForceAlignment.None))Public Sub Open()    Select Case ForceAlignment        Case enuForceAlignment.Left            OpenLeft()        Case enuForceAlignment.Right            OpenRight()        Case Else            IsOpen = True    End SelectEnd SubPublic Sub OpenRight()    _Open(False)End SubPublic Sub OpenLeft()    _Open(True)End SubPrivate Sub _Open(paMenuDropAlignment As Boolean)    If SystemParameters.MenuDropAlignment <> paMenuDropAlignment Then        moFI.SetValue(Nothing, paMenuDropAlignment)        IsOpen = True        moFI.SetValue(Nothing, Not paMenuDropAlignment)    Else        IsOpen = True    End IfEnd SubEnd Class

Set it to regular mode for your whole application:

FieldInfo fi = typeof(SystemParameters).GetField("_menuDropAlignment",   BindingFlags.NonPublic | BindingFlags.Static);fi.SetValue(null, false);

SystemParameters.MenuDropAlignment is used in a single method:

System.Windows.Controls.Primitives.Popup.GetPointCombination()

This private method has logic that depends upon the value of Popup.Placement, which is of type PlacementMode:

public enum PlacementMode{    Absolute,    Relative,    Bottom,    Center,    Right,    AbsolutePoint,    RelativePoint,    Mouse,    MousePoint,    Left,    Top,    Custom}

In GetPointCombination(), it only checks the MenuDropAlignment when the PlacementMode is Relative, AbsolutePoint, RelativePoint, or MousePoint. If you can use one of the other PlacementModes then you won't be subject to the MenuDropAlignment check.

If you use PlacementMode.Custom, then you'll also want to set the Popup.CustomPopupPlacementCallback to a valid method in order to provide your popup's CustomPopupPlacement[] coordinates.

Source: Reflector