Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / System / Windows / Documents / UIElementPropertyUndoUnit.cs / 1305600 / UIElementPropertyUndoUnit.cs
//---------------------------------------------------------------------------- // // 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 } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. 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