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//---------------------------------------------------------------------------
//
// File: UIElementPropertyUndoUnit.cs
//
// Description: Undo unit for property sets on UIElement.
// It is created for:
// 1. FlowDirectionProperty sets on a TextEditor's UI scope element.
// 2. HorizontalAlignmentProperty sets on UIElement child of BlockUIContainer.
//
// History:
// 01/13/2006 : pjoshi - Branched from FlowDirectionUndoUnit.cs
//
//---------------------------------------------------------------------------
using System;
using System.Windows;
using MS.Internal;
using MS.Internal.Documents;
namespace System.Windows.Documents
{
// 1. Undo unit for FlowDirectionProperty sets on a TextEditor's UI scope element.
//
// The TextEditor lets users configure the FlowDirection of text dynamically
// even when running on TextBoxes (TextEditor.AcceptsRichContent == false).
// In this case, there's no TextElement to hang property values on, so we must
// resort to assigning values directly to the TextEditor's UiScope, which is
// not covered by the TextContainer's undo infrastructure.
//
// This class encapsulates an undo unit used to track FlowDirection changes on
// plain text documents.
//
// 2. Undo unit for HorizontalAlignmentProperty sets on UIElement child of BlockUIContainer.
//
// When applying TextAlignment property to BlockUIContainer elements in rich text documents,
// text alignment must be translated into HorizontalAlignment of its child UIElement.
// We must assign this property value directly to the embedded UIElement.
// Since TextEditor's undo mechanism for property changes on TextElements in the tree relies
// on the OnPropertyChanged event listener, it is unable to track this property change.
// Also, it is infeasible to have a OnPropertyChanged listener for all UIElements.
// So we resort to explicitly adding this special undo unit in such situation.
//
internal class UIElementPropertyUndoUnit : IUndoUnit
{
//------------------------------------------------------
//
// Constructors
//
//------------------------------------------------------
#region Constructors
// Create a new undo unit instance.
private UIElementPropertyUndoUnit(UIElement uiElement, DependencyProperty property, object oldValue)
{
_uiElement = uiElement;
_property = property;
_oldValue = oldValue;
}
#endregion Constructors
//------------------------------------------------------
//
// Public Methods
//
//------------------------------------------------------
#region Public Methods
// Called by the undo manager. Restores tree state to its condition
// when the unit was created.
public void Do()
{
if (_oldValue != DependencyProperty.UnsetValue)
{
_uiElement.SetValue(_property, _oldValue);
}
else
{
_uiElement.ClearValue(_property);
}
}
// Called by the undo manager.
public bool Merge(IUndoUnit unit)
{
Invariant.Assert(unit != null);
return false;
}
#endregion Public Methods
//------------------------------------------------------
//
// Internal Methods
//
//------------------------------------------------------
#region Internal Methods
// Note that following strongly typed overloads of Add are meant to restrict the usage of UIElementPropertyUndoUnit
// for tracking changes to only a limited set of properties of UIElements.
// In general, it is not safe to keep a reference to the original property value, however for enum types, it is safe to do so.
// Add a new UIElementPropertyUndoUnit to the undo stack for HorizontalAlignment property.
internal static void Add(ITextContainer textContainer, UIElement uiElement, DependencyProperty property, HorizontalAlignment newValue)
{
AddPrivate(textContainer, uiElement, property, newValue);
}
// Add a new UIElementPropertyUndoUnit to the undo stack for FlowDirection property.
internal static void Add(ITextContainer textContainer, UIElement uiElement, DependencyProperty property, FlowDirection newValue)
{
AddPrivate(textContainer, uiElement, property, newValue);
}
#endregion Internal Methods
//------------------------------------------------------
//
// Privte Methods
//
//------------------------------------------------------
#region Private Methods
// Private helper that adds a new UIElementPropertyUndoUnit to the undo stack.
private static void AddPrivate(ITextContainer textContainer, UIElement uiElement, DependencyProperty property, object newValue)
{
UndoManager undoManager = TextTreeUndo.GetOrClearUndoManager(textContainer);
if (undoManager == null)
{
return;
}
object currentValue = uiElement.ReadLocalValue(property);
if (currentValue is Expression)
{
// Can't undo when old value is an expression, so clear the stack.
if (undoManager.IsEnabled)
{
undoManager.Clear();
}
return;
}
if (currentValue.Equals(newValue))
{
// No property change.
return;
}
undoManager.Add(new UIElementPropertyUndoUnit(uiElement, property, currentValue));
}
#endregion Private Methods
//------------------------------------------------------
//
// Private Fields
//
//------------------------------------------------------
#region Private Fields
// UIElement associated with this undo unit.
private readonly UIElement _uiElement;
// DependencyProperty of the UIElement associated with this undo unit.
private readonly DependencyProperty _property;
// Original property value.
private readonly object _oldValue;
#endregion Private Fields
}
}
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