More changes to the handling of invalid visual lines.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@3835 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/FoldingSection.cs

@@ -7,6 +7,7 @@
 
 using System;
 using ICSharpCode.AvalonEdit.Document;
+using System.Windows.Threading;
 
 namespace ICSharpCode.AvalonEdit.Gui
 {
@@ -40,7 +41,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 							collapsedSection = null;
 						}
 					}
-					manager.textView.Redraw();
+					manager.textView.Redraw(this, DispatcherPriority.Normal);
 				}
 			}
 		}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/NoReadOnlySections.cs

@@ -12,6 +12,9 @@ using System.Collections.Generic;
 
 namespace ICSharpCode.AvalonEdit.Gui
 {
+	/// <summary>
+	/// <see cref="IReadOnlySectionProvider"/> that has no read-only sections; all text is editable.
+	/// </summary>
 	sealed class NoReadOnlySections : IReadOnlySectionProvider
 	{
 		public static readonly NoReadOnlySections Instance = new NoReadOnlySections();

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/SelectionMouseHandler.cs

@@ -23,8 +23,43 @@ namespace ICSharpCode.AvalonEdit.Gui
 	/// </summary>
 	sealed class SelectionMouseHandler
 	{
+		#region enum SelectionMode
+		enum SelectionMode
+		{
+			/// <summary>
+			/// no selection (no mouse button down)
+			/// </summary>
+			None,
+			/// <summary>
+			/// left mouse button down on selection, might be normal click
+			/// or might be drag'n'drop
+			/// </summary>
+			PossibleDragStart,
+			/// <summary>
+			/// dragging text
+			/// </summary>
+			Drag,
+			/// <summary>
+			/// normal selection (click+drag)
+			/// </summary>
+			Normal,
+			/// <summary>
+			/// whole-word selection (double click+drag)
+			/// </summary>
+			WholeWord
+		}
+		#endregion
+		
+		// TODO: allow disabling text drag'n'drop
+		const bool AllowTextDragDrop = true;
+		
 		readonly TextArea textArea;
 		
+		SelectionMode mode;
+		AnchorSegment startWord;
+		Point possibleDragStartMousePos;
+		
+		#region Constructor + Attach + Detach
 		public SelectionMouseHandler(TextArea textArea)
 		{
 			this.textArea = textArea;
@@ -47,6 +82,26 @@ namespace ICSharpCode.AvalonEdit.Gui
 			}
 		}
 		
+		public void Detach()
+		{
+			mode = SelectionMode.None;
+			textArea.MouseLeftButtonDown -= textArea_MouseLeftButtonDown;
+			textArea.MouseMove -= textArea_MouseMove;
+			textArea.MouseLeftButtonUp -= textArea_MouseLeftButtonUp;
+			textArea.QueryCursor -= textArea_QueryCursor;
+			if (AllowTextDragDrop) {
+				textArea.AllowDrop = false;
+				textArea.GiveFeedback -= textArea_GiveFeedback;
+				textArea.QueryContinueDrag -= textArea_QueryContinueDrag;
+				textArea.DragEnter -= textArea_DragEnter;
+				textArea.DragOver -=  textArea_DragOver;
+				textArea.DragLeave -= textArea_DragLeave;
+				textArea.Drop -= textArea_Drop;
+			}
+		}
+		#endregion
+		
+		#region Dropping text
 		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes")]
 		void textArea_DragEnter(object sender, DragEventArgs e)
 		{
@@ -131,22 +186,60 @@ namespace ICSharpCode.AvalonEdit.Gui
 				           }));
 		}
 		
-		public void Detach()
+		void textArea_GiveFeedback(object sender, GiveFeedbackEventArgs e)
 		{
-			mode = SelectionMode.None;
-			textArea.MouseLeftButtonDown -= textArea_MouseLeftButtonDown;
-			textArea.MouseMove -= textArea_MouseMove;
-			textArea.MouseLeftButtonUp -= textArea_MouseLeftButtonUp;
-			textArea.QueryCursor -= textArea_QueryCursor;
-			if (AllowTextDragDrop) {
-				textArea.GiveFeedback -= textArea_GiveFeedback;
-				textArea.QueryContinueDrag -= textArea_QueryContinueDrag;
+			e.UseDefaultCursors = true;
+			e.Handled = true;
 		}
+		
+		void textArea_QueryContinueDrag(object sender, QueryContinueDragEventArgs e)
+		{
+			if (e.EscapePressed) {
+				e.Action = DragAction.Cancel;
+			} else if ((e.KeyStates & DragDropKeyStates.LeftMouseButton) != DragDropKeyStates.LeftMouseButton) {
+				e.Action = DragAction.Drop;
+			} else {
+				e.Action = DragAction.Continue;
 			}
+			e.Handled = true;
+		}
+		#endregion
 		
-		// TODO: allow disabling text drag'n'drop
-		const bool AllowTextDragDrop = true;
+		#region Start Drag
+		void StartDrag()
+		{
+			// prevent nested StartDrag calls
+			mode = SelectionMode.Drag;
+			
+			// mouse capture and Drag'n'Drop doesn't mix
+			textArea.ReleaseMouseCapture();
+			
+			string text = textArea.Selection.GetText(textArea.Document);
+			DataObject dataObject = new DataObject();
+			dataObject.SetText(text);
+			
+			DragDropEffects allowedEffects = DragDropEffects.All;
+			List<AnchorSegment> deleteOnMove;
+			deleteOnMove = textArea.Selection.Segments.Select(s => new AnchorSegment(textArea.Document, s)).ToList();
+			
+			Debug.WriteLine("DoDragDrop with allowedEffects=" + allowedEffects);
+			DragDropEffects resultEffect = DragDrop.DoDragDrop(textArea, dataObject, allowedEffects);
+			Debug.WriteLine("DoDragDrop done, resultEffect=" + resultEffect);
+			
+			if (deleteOnMove != null && resultEffect == DragDropEffects.Move) {
+				textArea.Document.BeginUpdate();
+				try {
+					foreach (ISegment s in deleteOnMove) {
+						textArea.Document.Remove(s.Offset, s.Length);
+					}
+				} finally {
+					textArea.Document.EndUpdate();
+				}
+			}
+		}
+		#endregion
 		
+		#region QueryCursor
 		// provide the IBeam Cursor for the text area
 		void textArea_QueryCursor(object sender, QueryCursorEventArgs e)
 		{
@@ -171,7 +264,9 @@ namespace ICSharpCode.AvalonEdit.Gui
 				}
 			}
 		}
+		#endregion
 		
+		#region ContainsOffset helper methods
 		static bool SelectionContains(Selection selection, int offset)
 		{
 			if (selection.IsEmpty)
@@ -194,36 +289,9 @@ namespace ICSharpCode.AvalonEdit.Gui
 			int end = start + segment.Length;
 			return offset >= start && offset <= end;
 		}
+		#endregion
 		
-		enum SelectionMode
-		{
-			/// <summary>
-			/// no selection (no mouse button down)
-			/// </summary>
-			None,
-			/// <summary>
-			/// left mouse button down on selection, might be normal click
-			/// or might be drag'n'drop
-			/// </summary>
-			PossibleDragStart,
-			/// <summary>
-			/// dragging text
-			/// </summary>
-			Drag,
-			/// <summary>
-			/// normal selection (click+drag)
-			/// </summary>
-			Normal,
-			/// <summary>
-			/// whole-word selection (double click+drag)
-			/// </summary>
-			WholeWord
-		}
-		
-		SelectionMode mode;
-		AnchorSegment startWord;
-		Point possibleDragStartMousePos;
-		
+		#region LeftButtonDown
 		void textArea_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
 		{
 			mode = SelectionMode.None;
@@ -279,7 +347,9 @@ namespace ICSharpCode.AvalonEdit.Gui
 			}
 			e.Handled = true;
 		}
+		#endregion
 		
+		#region Mouse Position <-> Text coordinates
 		SimpleSegment GetWordAtMousePosition(MouseEventArgs e)
 		{
 			TextView textView = textArea.TextView;
@@ -308,16 +378,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 			}
 		}
 		
-		void SetCaretOffsetToMousePosition(MouseEventArgs e)
-		{
-			int visualColumn;
-			int offset = GetOffsetFromMousePosition(e, out visualColumn);
-			if (offset >= 0) {
-				textArea.Caret.Position = new TextViewPosition(textArea.Document.GetLocation(offset), visualColumn);
-				textArea.Caret.DesiredXPos = double.NaN;
-			}
-		}
-		
 		int GetOffsetFromMousePosition(MouseEventArgs e, out int visualColumn)
 		{
 			return GetOffsetFromMousePosition(e.GetPosition(textArea.TextView), out visualColumn);
@@ -342,7 +402,9 @@ namespace ICSharpCode.AvalonEdit.Gui
 			}
 			return -1;
 		}
+		#endregion
 		
+		#region MouseMove
 		void textArea_MouseMove(object sender, MouseEventArgs e)
 		{
 			if (e.Handled)
@@ -365,6 +427,18 @@ namespace ICSharpCode.AvalonEdit.Gui
 				}
 			}
 		}
+		#endregion
+		
+		#region ExtendSelection
+		void SetCaretOffsetToMousePosition(MouseEventArgs e)
+		{
+			int visualColumn;
+			int offset = GetOffsetFromMousePosition(e, out visualColumn);
+			if (offset >= 0) {
+				textArea.Caret.Position = new TextViewPosition(textArea.Document.GetLocation(offset), visualColumn);
+				textArea.Caret.DesiredXPos = double.NaN;
+			}
+		}
 		
 		void ExtendSelectionToMouse(MouseEventArgs e)
 		{
@@ -379,7 +453,9 @@ namespace ICSharpCode.AvalonEdit.Gui
 				}
 			}
 		}
+		#endregion
 		
+		#region MouseLeftButtonUp
 		void textArea_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
 		{
 			if (mode == SelectionMode.None || e.Handled)
@@ -395,55 +471,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 			mode = SelectionMode.None;
 			textArea.ReleaseMouseCapture();
 		}
-		
-		void StartDrag()
-		{
-			// prevent nested StartDrag calls
-			mode = SelectionMode.Drag;
-			
-			// mouse capture and Drag'n'Drop doesn't mix
-			textArea.ReleaseMouseCapture();
-			
-			string text = textArea.Selection.GetText(textArea.Document);
-			DataObject dataObject = new DataObject();
-			dataObject.SetText(text);
-			
-			DragDropEffects allowedEffects = DragDropEffects.All;
-			List<AnchorSegment> deleteOnMove;
-			deleteOnMove = textArea.Selection.Segments.Select(s => new AnchorSegment(textArea.Document, s)).ToList();
-			
-			Debug.WriteLine("DoDragDrop with allowedEffects=" + allowedEffects);
-			DragDropEffects resultEffect = DragDrop.DoDragDrop(textArea, dataObject, allowedEffects);
-			Debug.WriteLine("DoDragDrop done, resultEffect=" + resultEffect);
-			
-			if (deleteOnMove != null && resultEffect == DragDropEffects.Move) {
-				textArea.Document.BeginUpdate();
-				try {
-					foreach (ISegment s in deleteOnMove) {
-						textArea.Document.Remove(s.Offset, s.Length);
-					}
-				} finally {
-					textArea.Document.EndUpdate();
-				}
-			}
-		}
-
-		void textArea_GiveFeedback(object sender, GiveFeedbackEventArgs e)
-		{
-			e.UseDefaultCursors = true;
-			e.Handled = true;
-		}
-		
-		void textArea_QueryContinueDrag(object sender, QueryContinueDragEventArgs e)
-		{
-			if (e.EscapePressed) {
-				e.Action = DragAction.Cancel;
-			} else if ((e.KeyStates & DragDropKeyStates.LeftMouseButton) != DragDropKeyStates.LeftMouseButton) {
-				e.Action = DragAction.Drop;
-			} else {
-				e.Action = DragAction.Continue;
-			}
-			e.Handled = true;
-		}
+		#endregion
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/TextArea.cs

@@ -8,6 +8,7 @@
 using System;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
+using System.Linq;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Controls.Primitives;
@@ -126,6 +127,7 @@ namespace ICSharpCode.AvalonEdit
 		}
 		#endregion
 		
+		#region Caret handling on document changes
 		bool IWeakEventListener.ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
 		{
 			if (managerType == typeof(TextDocumentWeakEventManager.Changing)) {
@@ -181,18 +183,37 @@ namespace ICSharpCode.AvalonEdit
 				Undo();
 			}
 		}
+		#endregion
 		
-		readonly Caret caret;
+		#region TextView property
+		readonly TextView textView;
+		IScrollInfo scrollInfo;
 
 		/// <summary>
-		/// Gets the Caret used for this text area.
+		/// Gets the text view used to display text in this text area.
 		/// </summary>
-		public Caret Caret {
-			get { return caret; }
+		public TextView TextView {
+			get {
+				return textView;
 			}
+		}
+		/// <inheritdoc/>
+		public override void OnApplyTemplate()
+		{
+			base.OnApplyTemplate();
+			scrollInfo = textView;
+			ApplyScrollInfo();
+		}
+		#endregion
 		
+		#region Selection property
 		Selection selection = Selection.Empty;
 		
+		/// <summary>
+		/// Occurs when the selection has changed.
+		/// </summary>
+		public event EventHandler SelectionChanged;
+		
 		/// <summary>
 		/// Gets/Sets the selection in this text area.
 		/// </summary>
@@ -213,30 +234,16 @@ namespace ICSharpCode.AvalonEdit
 				}
 			}
 		}
+		#endregion
 		
-		/// <summary>
-		/// Occurs when the selection has changed.
-		/// </summary>
-		public event EventHandler SelectionChanged;
-		
-		readonly TextView textView;
-		IScrollInfo scrollInfo;
-
-		/// <inheritdoc/>
-		public override void OnApplyTemplate()
-		{
-			base.OnApplyTemplate();
-			scrollInfo = textView;
-			ApplyScrollInfo();
-		}
+		#region Properties
+		readonly Caret caret;
 		
 		/// <summary>
-		/// Gets the text view used to display text in this text area.
+		/// Gets the Caret used for this text area.
 		/// </summary>
-		public TextView TextView {
-			get {
-				return textView;
-			}
+		public Caret Caret {
+			get { return caret; }
 		}
 		
 		ObservableCollection<UIElement> leftMargins = new ObservableCollection<UIElement>();
@@ -250,6 +257,21 @@ namespace ICSharpCode.AvalonEdit
 			}
 		}
 		
+		IReadOnlySectionProvider readOnlySectionProvider = NoReadOnlySections.Instance;
+		
+		/// <summary>
+		/// Gets/Sets an object that provides read-only sections for the text area.
+		/// </summary>
+		public IReadOnlySectionProvider ReadOnlySectionProvider {
+			get { return readOnlySectionProvider; }
+			set {
+				if (value == null)
+					throw new ArgumentNullException("value");
+				readOnlySectionProvider = value;
+			}
+		}
+		#endregion
+		
 		#region Undo / Redo
 		UndoStack GetUndoStack()
 		{
@@ -432,6 +454,7 @@ namespace ICSharpCode.AvalonEdit
 		}
 		#endregion
 		
+		#region Focus Handling (Show/Hide Caret)
 		/// <inheritdoc/>
 		protected override void OnMouseDown(MouseButtonEventArgs e)
 		{
@@ -454,21 +477,9 @@ namespace ICSharpCode.AvalonEdit
 			caret.Hide();
 			e.Handled = true;
 		}
+		#endregion
 		
-		IReadOnlySectionProvider readOnlySectionProvider = NoReadOnlySections.Instance;
-		
-		/// <summary>
-		/// Gets/Sets an object that provides read-only sections for the text area.
-		/// </summary>
-		public IReadOnlySectionProvider ReadOnlySectionProvider {
-			get { return readOnlySectionProvider; }
-			set {
-				if (value == null)
-					throw new ArgumentNullException("value");
-				readOnlySectionProvider = value;
-			}
-		}
-		
+		#region OnTextInput / RemoveSelectedText / ReplaceSelectionWithText
 		/// <inheritdoc/>
 		protected override void OnTextInput(TextCompositionEventArgs e)
 		{
@@ -476,14 +487,7 @@ namespace ICSharpCode.AvalonEdit
 			if (!e.Handled) {
 				TextDocument document = this.Document;
 				if (document != null) {
-					document.BeginUpdate();
-					try {
-						RemoveSelectedText();
-						if (readOnlySectionProvider.CanInsert(caret.Offset))
-							document.Insert(caret.Offset, e.Text);
-					} finally {
-						document.EndUpdate();
-					}
+					ReplaceSelectionWithText(e.Text);
 					caret.BringCaretToView();
 					e.Handled = true;
 				}
@@ -495,7 +499,9 @@ namespace ICSharpCode.AvalonEdit
 			selection.RemoveSelectedText(this);
 			#if DEBUG
 			if (!selection.IsEmpty) {
-				// TODO: assert that the remaining selection is read-only
+				foreach (ISegment s in selection.Segments) {
+					Debug.Assert(ReadOnlySectionProvider.GetDeletableSegments(s).Count() == 0);
+				}
 			}
 			#endif
 		}
@@ -512,5 +518,6 @@ namespace ICSharpCode.AvalonEdit
 				Document.EndUpdate();
 			}
 		}
+		#endregion
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/TextView.cs

@@ -26,9 +26,13 @@ namespace ICSharpCode.AvalonEdit.Gui
 {
 	/// <summary>
 	/// A virtualizing panel producing+showing <see cref="VisualLine"/>s for a <see cref="TextDocument"/>.
+	/// 
+	/// This is the heart of the text editor, this class controls the text rendering process.
+	/// 
+	/// Taken as a standalone control, it's a text viewer without any editing capability.
 	/// </summary>
 	[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1001:TypesThatOwnDisposableFieldsShouldBeDisposable",
-	                                                 Justification = "The user usually doesn't work with TextView but with TextEditor; nulling the Document property is sufficient to dispose everything.")]
+	                                                 Justification = "The user usually doesn't work with TextView but with TextEditor; and nulling the Document property is sufficient to dispose everything.")]
 	public class TextView : FrameworkElement, IScrollInfo, IWeakEventListener
 	{
 		#region Constructor
@@ -50,7 +54,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 		}
 		#endregion
 		
-		#region Properties
+		#region Document Property
 		/// <summary>
 		/// Document property.
 		/// </summary>
@@ -119,6 +123,7 @@ namespace ICSharpCode.AvalonEdit.Gui
 		}
 		#endregion
 		
+		#region Collection Properties
 		readonly ObservableCollection<VisualLineElementGenerator> elementGenerators = new ObservableCollection<VisualLineElementGenerator>();
 		
 		/// <summary>
@@ -145,13 +150,15 @@ namespace ICSharpCode.AvalonEdit.Gui
 		public UIElementCollection Adorners {
 			get { return adorners; }
 		}
+		#endregion
 		
+		#region Redraw methods / VisualLine invalidation
 		/// <summary>
 		/// Causes the text editor to regenerate all visual lines.
 		/// </summary>
 		public void Redraw()
 		{
-			Redraw(DispatcherPriority.Render);
+			Redraw(DispatcherPriority.Normal);
 		}
 		
 		/// <summary>
@@ -183,7 +190,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 		public void Redraw(int offset, int length, DispatcherPriority redrawPriority)
 		{
 			VerifyAccess();
-			if (allVisualLines.Count != 0 || visibleVisualLines != null) {
 			bool removedLine = false;
 			for (int i = 0; i < allVisualLines.Count; i++) {
 				VisualLine visualLine = allVisualLines[i];
@@ -200,7 +206,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 				InvalidateMeasure(redrawPriority);
 			}
 		}
-		}
 		
 		/// <summary>
 		/// Causes the text editor to redraw all lines overlapping with the specified segment.
@@ -213,6 +218,36 @@ namespace ICSharpCode.AvalonEdit.Gui
 			}
 		}
 		
+		/// <summary>
+		/// Invalidates all visual lines.
+		/// The caller of ClearVisualLines() must also call InvalidateMeasure() to ensure
+		/// that the visual lines will be recreated.
+		/// </summary>
+		void ClearVisualLines()
+		{
+			visibleVisualLines = null;
+			if (allVisualLines.Count != 0) {
+				foreach (VisualLine visualLine in allVisualLines) {
+					DisposeVisualLine(visualLine);
+				}
+				allVisualLines.Clear();
+			}
+		}
+		
+		void DisposeVisualLine(VisualLine visualLine)
+		{
+			if (newVisualLines != null && newVisualLines.Contains(visualLine)) {
+				throw new ArgumentException("Cannot dispose visual line because it is in construction!");
+			}
+			visualLine.IsDisposed = true;
+			foreach (TextLine textLine in visualLine.TextLines) {
+				textLine.Dispose();
+			}
+			RemoveInlineObjects(visualLine);
+		}
+		#endregion
+		
+		#region InvalidateMeasure(DispatcherPriority)
 		DispatcherOperation invalidateMeasureOperation;
 		
 		void InvalidateMeasure(DispatcherPriority priority)
@@ -239,44 +274,9 @@ namespace ICSharpCode.AvalonEdit.Gui
 				}
 			}
 		}
+		#endregion
 		
-		/// <summary>
-		/// Waits for the visual lines to be built.
-		/// </summary>
-		private void EnsureVisualLines()
-		{
-			Dispatcher.VerifyAccess();
-			if (visibleVisualLines == null) {
-				// increase priority for real Redraw
-				InvalidateMeasure(DispatcherPriority.Normal);
-				// force immediate re-measure
-				UpdateLayout();
-			}
-		}
-		
-		void ClearVisualLines()
-		{
-			visibleVisualLines = null;
-			if (allVisualLines.Count != 0) {
-				foreach (VisualLine visualLine in allVisualLines) {
-					DisposeVisualLine(visualLine);
-				}
-				allVisualLines.Clear();
-			}
-		}
-		
-		void DisposeVisualLine(VisualLine visualLine)
-		{
-			if (newVisualLines != null && newVisualLines.Contains(visualLine)) {
-				throw new ArgumentException("Cannot dispose visual line because it is in construction!");
-			}
-			visualLine.IsDisposed = true;
-			foreach (TextLine textLine in visualLine.TextLines) {
-				textLine.Dispose();
-			}
-			RemoveInlineObjects(visualLine);
-		}
-		
+		#region Get(OrConstruct)VisualLine
 		/// <summary>
 		/// Gets the visual line that contains the document line with the specified number.
 		/// Returns null if the document line is outside the visible range.
@@ -324,39 +324,27 @@ namespace ICSharpCode.AvalonEdit.Gui
 			}
 			return l;
 		}
+		#endregion
 		
-		/// <summary>
-		/// Collapses lines for the purpose of scrolling. This method is meant for
-		/// <see cref="VisualLineElementGenerator"/>s that cause <see cref="VisualLine"/>s to span
-		/// multiple <see cref="DocumentLine"/>s. Do not call it without providing a corresponding
-		/// <see cref="VisualLineElementGenerator"/>.
-		/// If you want to create collapsible text sections, see <see cref="FoldingManager"/>.
-		/// </summary>
-		public CollapsedLineSection CollapseLines(DocumentLine start, DocumentLine end)
-		{
-			VerifyAccess();
-			return heightTree.CollapseText(start, end);
-		}
-		
-		/// <summary>
-		/// Gets the height of the document.
-		/// </summary>
-		public double DocumentHeight {
-			get { return heightTree.TotalHeight; }
-		}
-		
-		#region Measure
-		TextFormatter formatter;
+		#region Visual Lines (fields and properties)
 		List<VisualLine> allVisualLines = new List<VisualLine>();
 		ReadOnlyCollection<VisualLine> visibleVisualLines;
 		double clippedPixelsOnTop;
+		List<VisualLine> newVisualLines;
 		
 		/// <summary>
 		/// Gets the currently visible visual lines.
 		/// </summary>
+		/// <exception cref="VisualLinesInvalidException">
+		/// Gets thrown if there are invalid visual lines when this property is accessed.
+		/// You can use the <see cref="VisualLinesValid"/> property to check for this case,
+		/// or use the <see cref="EnsureVisualLines()"/> method to force creating the visual lines
+		/// when they are invalid.
+		/// </exception>
 		public ReadOnlyCollection<VisualLine> VisualLines {
 			get {
-				EnsureVisualLines();
+				if (visibleVisualLines == null)
+					throw new VisualLinesInvalidException();
 				return visibleVisualLines;
 			}
 		}
@@ -375,56 +363,75 @@ namespace ICSharpCode.AvalonEdit.Gui
 		/// </summary>
 		public event EventHandler VisualLinesChanged;
 		
-		TextRunProperties CreateGlobalTextRunProperties()
+		/// <summary>
+		/// If the visual lines are invalid, creates new visual lines for the visible part
+		/// of the document.
+		/// If all visual lines are valid, this method does nothing.
+		/// </summary>
+		/// <exception cref="InvalidOperationException">The visual line build process is already running.
+		/// It is not allowed to call this method during the construction of a visual line.</exception>
+		public void EnsureVisualLines()
 		{
-			return new GlobalTextRunProperties {
-				typeface = this.CreateTypeface(),
-				fontRenderingEmSize = LineHeight,
-				foregroundBrush = (Brush)GetValue(Control.ForegroundProperty),
-				cultureInfo = CultureInfo.CurrentCulture
-			};
+			Dispatcher.VerifyAccess();
+			if (inMeasure)
+				throw new InvalidOperationException("The visual line build process is already running! Cannot EnsureVisualLines() during Measure!");
+			if (visibleVisualLines == null) {
+				// increase priority for re-measure
+				InvalidateMeasure(DispatcherPriority.Normal);
+				// force immediate re-measure
+				UpdateLayout();
 			}
-		
-		TextParagraphProperties CreateParagraphProperties(TextRunProperties defaultTextRunProperties)
-		{
-			return new VisualLineTextParagraphProperties {
-				defaultTextRunProperties = defaultTextRunProperties,
-				textWrapping = canHorizontallyScroll ? TextWrapping.NoWrap : TextWrapping.Wrap,
-				tabSize = 4 * WideSpaceWidth
-			};
 		}
+		#endregion
 		
+		#region Measure
 		Size lastAvailableSize;
-		List<VisualLine> newVisualLines;
+		bool inMeasure;
 		
-		/// <summary>
-		/// Measure implementation.
-		/// </summary>
+		/// <inheritdoc/>
 		protected override Size MeasureOverride(Size availableSize)
 		{
 			if (!canHorizontallyScroll && !availableSize.Width.IsClose(lastAvailableSize.Width))
 				ClearVisualLines();
 			lastAvailableSize = availableSize;
-			return DoMeasure(availableSize);
-		}
 			
-		/// <summary>
-		/// Immediately performs the text creation.
-		/// </summary>
-		/// <param name="availableSize">The size of the text view.</param>
-		/// <returns></returns>
-		Size DoMeasure(Size availableSize)
-		{
-			bool isRealMeasure = true;
-			if (isRealMeasure)
 			RemoveInlineObjectsNow();
 			
 			if (document == null)
 				return Size.Empty;
 			
+			InvalidateVisual(); // = InvalidateArrange+InvalidateRender
+			
+			double maxWidth;
+			inMeasure = true;
+			try {
+				maxWidth = CreateAndMeasureVisualLines(availableSize);
+			} finally {
+				inMeasure = false;
+			}
+			
+			RemoveInlineObjectsNow();
+			
+			SetScrollData(availableSize,
+			              new Size(maxWidth, heightTree.TotalHeight),
+			              scrollOffset);
+			if (VisualLinesChanged != null)
+				VisualLinesChanged(this, EventArgs.Empty);
+			if (canHorizontallyScroll) {
+				return availableSize;
+			} else {
+				return new Size(maxWidth, availableSize.Height);
+			}
+		}
+		
+		/// <summary>
+		/// Build all VisualLines in the visible range.
+		/// </summary>
+		/// <returns>Width the longest line</returns>
+		double CreateAndMeasureVisualLines(Size availableSize)
+		{
 			TextRunProperties globalTextRunProperties = CreateGlobalTextRunProperties();
 			TextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
-			InvalidateVisual(); // = InvalidateArrange+InvalidateRender
 			
 			Debug.WriteLine("Measure availableSize=" + availableSize + ", scrollOffset=" + scrollOffset);
 			var firstLineInView = heightTree.GetLineByVisualPosition(scrollOffset.Y);
@@ -472,8 +479,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 				if (!newVisualLines.Contains(line))
 					DisposeVisualLine(line);
 			}
-			if (isRealMeasure)
-				RemoveInlineObjectsNow();
 			
 			allVisualLines = newVisualLines;
 			// visibleVisualLines = readonly copy of visual lines
@@ -485,17 +490,30 @@ namespace ICSharpCode.AvalonEdit.Gui
 				                                    "This can happen when Redraw() is called during measure for lines " +
 				                                    "that are already constructed.");
 			}
+			return maxWidth;
+		}
+		#endregion
 		
-			SetScrollData(availableSize,
-			              new Size(maxWidth, heightTree.TotalHeight),
-			              scrollOffset);
-			if (VisualLinesChanged != null)
-				VisualLinesChanged(this, EventArgs.Empty);
-			if (canHorizontallyScroll) {
-				return availableSize;
-			} else {
-				return new Size(maxWidth, availableSize.Height);
+		#region BuildVisualLine
+		TextFormatter formatter;
+		
+		TextRunProperties CreateGlobalTextRunProperties()
+		{
+			return new GlobalTextRunProperties {
+				typeface = this.CreateTypeface(),
+				fontRenderingEmSize = LineHeight,
+				foregroundBrush = (Brush)GetValue(Control.ForegroundProperty),
+				cultureInfo = CultureInfo.CurrentCulture
+			};
 		}
+		
+		TextParagraphProperties CreateParagraphProperties(TextRunProperties defaultTextRunProperties)
+		{
+			return new VisualLineTextParagraphProperties {
+				defaultTextRunProperties = defaultTextRunProperties,
+				textWrapping = canHorizontallyScroll ? TextWrapping.NoWrap : TextWrapping.Wrap,
+				tabSize = 4 * WideSpaceWidth
+			};
 		}
 		
 		VisualLine BuildVisualLine(DocumentLine documentLine,
@@ -969,17 +987,6 @@ namespace ICSharpCode.AvalonEdit.Gui
 		}
 		#endregion
 		
-		/// <summary>
-		/// Gets the document line at the specified visual position.
-		/// </summary>
-		public DocumentLine GetDocumentLineByVisualTop(double visualTop)
-		{
-			VerifyAccess();
-			if (heightTree == null)
-				throw new InvalidOperationException();
-			return heightTree.GetLineByVisualPosition(visualTop);
-		}
-		
 		#region Visual element mouse handling
 		/// <inheritdoc/>
 		protected override HitTestResult HitTestCore(PointHitTestParameters hitTestParameters)
@@ -1041,15 +1048,17 @@ namespace ICSharpCode.AvalonEdit.Gui
 				}
 			}
 		}
+		#endregion
 		
+		#region Getting elements from Visual Position
 		/// <summary>
 		/// Gets the visual line at the specified document position (relative to start of document).
 		/// Returns null if there is no visual line for the position (e.g. the position is outside the visible
 		/// text area).
-		/// You may want to call <see cref="EnsureVisualLines"/>() before calling this method.
 		/// </summary>
 		public VisualLine GetVisualLineFromVisualTop(double visualTop)
 		{
+			EnsureVisualLines();
 			foreach (VisualLine vl in this.VisualLines) {
 				if (visualTop < vl.VisualTop)
 					continue;
@@ -1074,5 +1083,36 @@ namespace ICSharpCode.AvalonEdit.Gui
 			return null;
 		}
 		#endregion
+		
+		/// <summary>
+		/// Collapses lines for the purpose of scrolling. This method is meant for
+		/// <see cref="VisualLineElementGenerator"/>s that cause <see cref="VisualLine"/>s to span
+		/// multiple <see cref="DocumentLine"/>s. Do not call it without providing a corresponding
+		/// <see cref="VisualLineElementGenerator"/>.
+		/// If you want to create collapsible text sections, see <see cref="FoldingManager"/>.
+		/// </summary>
+		public CollapsedLineSection CollapseLines(DocumentLine start, DocumentLine end)
+		{
+			VerifyAccess();
+			return heightTree.CollapseText(start, end);
+		}
+		
+		/// <summary>
+		/// Gets the height of the document.
+		/// </summary>
+		public double DocumentHeight {
+			get { return heightTree.TotalHeight; }
+		}
+		
+		/// <summary>
+		/// Gets the document line at the specified visual position.
+		/// </summary>
+		public DocumentLine GetDocumentLineByVisualTop(double visualTop)
+		{
+			VerifyAccess();
+			if (heightTree == null)
+				throw new InvalidOperationException();
+			return heightTree.GetLineByVisualPosition(visualTop);
+		}
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Gui/VisualLinesInvalidException.cs

@@ -0,0 +1,48 @@
+// <file>
+//     <copyright see="prj:///doc/copyright.txt"/>
+//     <license see="prj:///doc/license.txt"/>
+//     <author name="Daniel Grunwald"/>
+//     <version>$Revision$</version>
+// </file>
+
+using System;
+using System.Runtime.Serialization;
+
+namespace ICSharpCode.AvalonEdit.Gui
+{
+	/// <summary>
+	/// A VisualLinesInvalidException indicates that you accessed the <see cref="TextView.VisualLines"/> property
+	/// of the <see cref="TextView"/> while the visual lines were invalid.
+	/// </summary>
+	[Serializable]
+	public class VisualLinesInvalidException  : Exception
+	{
+		/// <summary>
+		/// Creates a new VisualLinesInvalidException instance.
+		/// </summary>
+		public VisualLinesInvalidException() : base()
+		{
+		}
+		
+		/// <summary>
+		/// Creates a new VisualLinesInvalidException instance.
+		/// </summary>
+		public VisualLinesInvalidException(string message) : base(message)
+		{
+		}
+		
+		/// <summary>
+		/// Creates a new VisualLinesInvalidException instance.
+		/// </summary>
+		public VisualLinesInvalidException(string message, Exception innerException) : base(message, innerException)
+		{
+		}
+		
+		/// <summary>
+		/// Creates a new VisualLinesInvalidException instance.
+		/// </summary>
+		protected VisualLinesInvalidException(SerializationInfo info, StreamingContext context) : base(info, context)
+		{
+		}
+	}
+}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/ICSharpCode.AvalonEdit.csproj

@@ -168,6 +168,7 @@
     <Compile Include="Gui\VisualLineElement.cs" />
     <Compile Include="Gui\VisualLineElementGenerator.cs">
     </Compile>
+    <Compile Include="Gui\VisualLinesInvalidException.cs" />
     <Compile Include="Gui\VisualLineText.cs" />
     <Compile Include="Gui\VisualLineTextParagraphProperties.cs">
       <DependentUpon>VisualLine.cs</DependentUpon>