support a contextmenu in AvaloniaEdit

MdXaml/Markdown.cs

@@ -15,6 +15,7 @@
 using System.IO;
 using System.Threading.Tasks;
 using System.Windows.Threading;
+using MdXaml.Menus;
 
 // I will not add System.Index and System.Range. There is not exist with net45.
 #pragma warning disable IDE0056
@@ -1492,6 +1493,8 @@ private Block CodeBlocksEvaluator(string? lang, string code)
 
 
             var result = new BlockUIContainer(txtEdit);
+            CommandsForTextEditor.Setup(txtEdit);
+
             if (CodeBlockStyle is not null)
             {
                 result.Style = CodeBlockStyle;

MdXaml/MarkdownScrollViewer.cs

@@ -336,6 +336,13 @@ public MarkdownScrollViewer()
                 _engine.DocumentStyle = MarkdownStyle;
 
             UpdateClickAction();
+
+
+            var menu = new ContextMenu();
+            menu.Items.Add(ApplicationCommands.Copy);
+            menu.Items.Add(ApplicationCommands.SelectAll);
+
+            ContextMenu = menu;
         }
 
         private void UpdateClickAction()

MdXaml/Menus/CommandsForTextEditor.cs

@@ -0,0 +1,92 @@
+using ICSharpCode.AvalonEdit;
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Input;
+
+namespace MdXaml.Menus
+{
+    public static class CommandsForTextEditor
+    {
+
+        public static void Setup(TextEditor editor)
+        {
+            editor.ContextMenuOpening += Editor_ContextMenuOpening;
+
+            var menu = new ContextMenu();
+            menu.Items.Add(new MenuItem()
+            {
+                Name = ApplicationCommands.Copy.Name,
+                Header = ApplicationCommands.Copy.Text,
+                InputGestureText = ExtractShortcut(ApplicationCommands.Copy.InputGestures),
+                Command = new TextEditorCopyCommand(editor)
+            });
+            menu.Items.Add(new MenuItem()
+            {
+                Name = ApplicationCommands.SelectAll.Name,
+                Header = ApplicationCommands.SelectAll.Text,
+                InputGestureText = ExtractShortcut(ApplicationCommands.SelectAll.InputGestures),
+                Command = new TextEditorSelectAllCommand(editor)
+            });
+
+            editor.ContextMenu = menu;
+
+        }
+
+        private static void Editor_ContextMenuOpening(object sender, ContextMenuEventArgs e)
+        {
+            if (sender is TextEditor editor)
+            {
+                var viewer = WalkParent<FlowDocumentScrollViewer>(editor);
+
+                if (viewer is null)
+                    return;
+
+                if (viewer.Selection is not null
+                    && !viewer.Selection.IsEmpty)
+                {
+                    viewer.IsSelectionEnabled = false;
+                    viewer.IsSelectionEnabled = true;
+                }
+            }
+        }
+
+        private static T? WalkParent<T>(FrameworkElement start)
+            where T : class
+        {
+            DependencyObject dobj = start.Parent;
+            for (; ; )
+            {
+                if (dobj is T t)
+                {
+                    return t;
+                }
+                else if (dobj is FrameworkElement element)
+                {
+                    dobj = element.Parent;
+                }
+                else if (dobj is FrameworkContentElement content)
+                {
+                    dobj = content.Parent;
+                }
+                else return null;
+            }
+        }
+
+        private static string? ExtractShortcut(InputGestureCollection? collection)
+        {
+            if (collection is null)
+                return "";
+
+            return collection.OfType<KeyGesture>()
+                             .Select(g => g.GetDisplayStringForCulture(CultureInfo.CurrentCulture))
+                             .FirstOrDefault()
+                   ?? "";
+        }
+    }
+}

MdXaml/Menus/TextEditorCopyCommand.cs

@@ -0,0 +1,42 @@
+using ICSharpCode.AvalonEdit;
+using System;
+using System.Windows.Controls;
+using System.Windows.Input;
+
+namespace MdXaml.Menus
+{
+    public class TextEditorCopyCommand : ICommand
+    {
+        public event EventHandler? CanExecuteChanged;
+
+        private TextEditor _editor;
+        private bool _isExecutable;
+
+        public TextEditorCopyCommand(TextEditor editor)
+        {
+            _editor = editor;
+            _editor.ContextMenuOpening += TryUpdateExecutable;
+        }
+
+        private void TryUpdateExecutable(object sender, ContextMenuEventArgs e)
+        {
+            var isExecutable = _editor.SelectionLength != 0;
+
+            if (_isExecutable != isExecutable)
+            {
+                _isExecutable = isExecutable;
+                CanExecuteChanged?.Invoke(this, EventArgs.Empty);
+            }
+        }
+
+        public bool CanExecute(object parameter)
+        {
+            return _isExecutable;
+        }
+
+        public void Execute(object parameter)
+        {
+            _editor.Copy();
+        }
+    }
+}

MdXaml/Menus/TextEditorSelectAllCommand.cs

@@ -0,0 +1,32 @@
+using ICSharpCode.AvalonEdit;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Input;
+
+namespace MdXaml.Menus
+{
+    public class TextEditorSelectAllCommand : ICommand
+    {
+        public event EventHandler? CanExecuteChanged;
+
+        private TextEditor _editor;
+
+        public TextEditorSelectAllCommand(TextEditor editor)
+        {
+            _editor = editor;
+        }
+
+        public bool CanExecute(object parameter)
+        {
+            return true;
+        }
+
+        public void Execute(object parameter)
+        {
+            _editor.SelectAll();
+        }
+    }
+}