From 7e9e7613bac34962c126ddaeaec899956e1d8a6c Mon Sep 17 00:00:00 2001
From: Paul Schneider <paul@pschneider.fr>
Date: Sun, 4 Oct 2026 20:03:01 +0100
Subject: [PATCH] Fix markdown draft preview sync in PostIt blog editor

---
 .../Controls/MarkdownEditorControl.axaml      |  51 +++++++
 .../Controls/MarkdownEditorControl.axaml.cs   |  63 +++++++++
 .../PostIt/ViewModels/Blogs/BlogsViewModel.cs |  52 ++++++-
 src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml | 133 +++++++-----------
 4 files changed, 209 insertions(+), 90 deletions(-)
 create mode 100644 src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml
 create mode 100644 src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml.cs

diff --git a/src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml b/src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml
new file mode 100644
index 000000000..7c639043d
--- /dev/null
+++ b/src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml
@@ -0,0 +1,51 @@
+<UserControl
+    x:Class="PostIt.Controls.MarkdownEditorControl"
+    xmlns="https://github.com/avaloniaui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:AvaloniaEdit="clr-namespace:AvaloniaEdit;assembly=AvaloniaEdit"
+    xmlns:md="using:MarkdownViewer.Core.Controls"
+    x:Name="Root"
+    HorizontalAlignment="Stretch"
+    VerticalAlignment="Stretch">
+    <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
+        <Border
+            BorderBrush="LightGray"
+            BorderThickness="1"
+            CornerRadius="5"
+            IsVisible="{Binding !IsPreviewVisible, ElementName=Root}"
+            Padding="0">
+            <AvaloniaEdit:TextEditor
+                x:Name="SourceEditor"
+                Document="{Binding Document, ElementName=Root, Mode=TwoWay}"
+                FontFamily="Cascadia Code,Consolas,Menlo,Monospace"
+                ShowLineNumbers="True"
+                WordWrap="True"
+                BorderThickness="0"
+                Padding="5,5,5,15"
+                HorizontalAlignment="Stretch"
+                VerticalAlignment="Stretch"
+                HorizontalScrollBarVisibility="Disabled"
+                TextInputOptions.Multiline="True"
+                TextInputOptions.ReturnKeyType="Default" />
+        </Border>
+
+        <Border
+            BorderBrush="LightGray"
+            BorderThickness="1"
+            CornerRadius="5"
+            IsVisible="{Binding IsPreviewVisible, ElementName=Root}"
+            Padding="8">
+            <ScrollViewer
+                BringIntoViewOnFocusChange="False"
+                HorizontalScrollBarVisibility="Disabled"
+                VerticalScrollBarVisibility="Auto"
+                HorizontalAlignment="Stretch"
+                VerticalAlignment="Stretch">
+                <md:MarkdownViewer
+                    x:Name="PreviewViewer"
+                    MarkdownText="{Binding MarkdownText, ElementName=Root}"
+                    ClipToBounds="False" />
+            </ScrollViewer>
+        </Border>
+    </Grid>
+</UserControl>
diff --git a/src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml.cs b/src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml.cs
new file mode 100644
index 000000000..2538f7168
--- /dev/null
+++ b/src/PostIt/PostIt/Controls/MarkdownEditorControl.axaml.cs
@@ -0,0 +1,63 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using AvaloniaEdit.Document;
+
+namespace PostIt.Controls;
+
+public partial class MarkdownEditorControl : UserControl
+{
+    public static readonly StyledProperty<string?> MarkdownTextProperty =
+        AvaloniaProperty.Register<MarkdownEditorControl, string?>(nameof(MarkdownText));
+
+    public static readonly StyledProperty<TextDocument?> DocumentProperty =
+        AvaloniaProperty.Register<MarkdownEditorControl, TextDocument?>(nameof(Document));
+
+    public static readonly StyledProperty<bool> IsPreviewVisibleProperty =
+        AvaloniaProperty.Register<MarkdownEditorControl, bool>(nameof(IsPreviewVisible), false);
+
+    public string? MarkdownText
+    {
+        get => GetValue(MarkdownTextProperty);
+        set => SetValue(MarkdownTextProperty, value);
+    }
+
+    public TextDocument? Document
+    {
+        get => GetValue(DocumentProperty);
+        set => SetValue(DocumentProperty, value);
+    }
+
+    public bool IsPreviewVisible
+    {
+        get => GetValue(IsPreviewVisibleProperty);
+        set => SetValue(IsPreviewVisibleProperty, value);
+    }
+
+    public MarkdownEditorControl()
+    {
+        InitializeComponent();
+        PropertyChanged += OnPropertyChanged;
+    }
+
+    private void OnPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
+    {
+        if (e.Property == MarkdownTextProperty)
+        {
+            var text = e.NewValue as string ?? string.Empty;
+            if (Document is null || !string.Equals(Document.Text, text, StringComparison.Ordinal))
+            {
+                Document = new TextDocument(text);
+            }
+        }
+        else if (e.Property == DocumentProperty)
+        {
+            var newDocument = e.NewValue as TextDocument;
+            var text = newDocument?.Text ?? string.Empty;
+            if (!string.Equals(MarkdownText, text, StringComparison.Ordinal))
+            {
+                MarkdownText = text;
+            }
+        }
+    }
+}
diff --git a/src/PostIt/PostIt/ViewModels/Blogs/BlogsViewModel.cs b/src/PostIt/PostIt/ViewModels/Blogs/BlogsViewModel.cs
index 6fe6eccc9..9de63c24c 100644
--- a/src/PostIt/PostIt/ViewModels/Blogs/BlogsViewModel.cs
+++ b/src/PostIt/PostIt/ViewModels/Blogs/BlogsViewModel.cs
@@ -39,18 +39,56 @@ public partial class BlogsViewModel : ViewModelBase, IActionStatusViewModel
     /// <summary>Editor buffer for the post body. Same pattern as
     /// <see cref="DraftTitle"/>.</summary>
 
-    public string DraftArticle
+    public string? DraftArticle
      {
-        get => DraftArticleDocument.Text;
-        set  {
+        get => DraftArticleDocument?.Text ?? null;
+        set
+        {
+            var currentText = DraftArticleDocument?.Text;
+            if (string.Equals(currentText, value, StringComparison.Ordinal))
+            {
+                OnPropertyChanged(nameof(DraftArticle));
+                return;
+            }
+
             OnPropertyChanging(nameof(DraftArticle));
-            DraftArticleDocument = new TextDocument(value);
-            this.OnPropertyChanged(nameof(DraftArticle));
+            DraftArticleDocument = value is not null ? new TextDocument(value) : null;
+            OnPropertyChanged(nameof(DraftArticle));
         }
      }
 
-    [ObservableProperty]
-    public partial TextDocument DraftArticleDocument {get; set;}
+    private TextDocument? _draftArticleDocument;
+
+    public TextDocument? DraftArticleDocument
+    {
+        get => _draftArticleDocument;
+        set
+        {
+            if (ReferenceEquals(_draftArticleDocument, value))
+            {
+                return;
+            }
+
+            if (_draftArticleDocument is not null)
+            {
+                _draftArticleDocument.TextChanged -= DraftArticleDocument_TextChanged;
+            }
+
+            _draftArticleDocument = value;
+
+            if (_draftArticleDocument is not null)
+            {
+                _draftArticleDocument.TextChanged += DraftArticleDocument_TextChanged;
+            }
+
+            OnPropertyChanged(nameof(DraftArticleDocument));
+        }
+    }
+
+    private void DraftArticleDocument_TextChanged(object? sender, EventArgs e)
+    {
+        OnPropertyChanged(nameof(DraftArticle));
+    }
 
     /// <summary>Editor buffer for the post's publication state.
     /// Reflects the server-side <c>IsPublished</c> flag (the
diff --git a/src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml b/src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml
index 90397f09d..f8534a094 100644
--- a/src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml
+++ b/src/PostIt/PostIt/Views/Blogs/BlogsPage.axaml
@@ -17,10 +17,7 @@
   <Design.DataContext>
     <vm:BlogsViewModel />
   </Design.DataContext>
-  <ScrollViewer HorizontalScrollBarVisibility="Disabled"
-    Margin="5,5,10,5" HorizontalAlignment="Stretch" BringIntoViewOnFocusChange="False"
-    VerticalAlignment="Stretch">
-    <StackPanel>
+  <StackPanel Margin="5,5,10,5" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
 
       <WrapPanel x:Name="BlogsHeaderPanel"
         Margin="5"
@@ -87,7 +84,7 @@
               <PathIcon Data="{StaticResource PublishedIcon}" />
             </CommandBarToggleButton.Icon>
           </CommandBarToggleButton>
-          <CommandBarToggleButton IsChecked="{Binding IsMarkdownViewerVisible, Mode=TwoWay}" Label="Markdown Viewer">
+          <CommandBarToggleButton IsChecked="{Binding IsMarkdownViewerVisible, Mode=TwoWay}" Label="Aperçu">
             <CommandBarToggleButton.Icon>
               <PathIcon Data="{StaticResource MarkdownIcon}" />
             </CommandBarToggleButton.Icon>
@@ -137,91 +134,61 @@
           </ListBox>
         </Border>
 
-        <Border
+        <Grid
           Grid.Row="2"
-          Padding="8"
+          HorizontalAlignment="Stretch"
+          VerticalAlignment="Stretch"
+          RowSpacing="10">
+          <Grid.RowDefinitions>
+            <RowDefinition Height="Auto" />
+            <RowDefinition Height="Auto" />
+            <RowDefinition Height="*" />
+            <RowDefinition Height="Auto" />
+          </Grid.RowDefinitions>
+          <Grid.ColumnDefinitions>
+            <ColumnDefinition Width="*" />
+          </Grid.ColumnDefinitions>
+
+          <TextBlock
+            Grid.Row="0"
+            FontWeight="SemiBold"
+            Text="Post detail" />
+          <TextBox
+            x:Name="DraftTitleTextBox"
+            Grid.Row="1"
+            PlaceholderText="Title"
+            Text="{Binding DraftTitle, Mode=TwoWay}" />
+
+          <postitControls:MarkdownEditorControl
+            Grid.Row="2"
             HorizontalAlignment="Stretch"
             VerticalAlignment="Stretch"
-          BorderBrush="Gray"
-          BorderThickness="1"
-          IsVisible="{Binding IsMarkdownViewerVisible}">
-          <md:MarkdownViewer Name="MarkdownViewer" MarkdownText="{Binding DraftArticle}" />
-        </Border>
+            IsPreviewVisible="{Binding IsMarkdownViewerVisible, Mode=TwoWay}"
+            MarkdownText="{Binding DraftArticle, Mode=TwoWay}"
+            Document="{Binding DraftArticleDocument, Mode=TwoWay}" />
 
-        <Border
-          Grid.Row="2"
-          Padding="8"
-          BorderBrush="Gray"
-          BorderThickness="1"
+          <Border x:Name="AttachmentsBorder"
+            Grid.Row="3"
+            Padding="8"
+            BorderBrush="LightGray"
+            BorderThickness="1"
             HorizontalAlignment="Stretch"
-            VerticalAlignment="Stretch"
-          IsVisible="{Binding !IsMarkdownViewerVisible}">
-          <Grid
-            HorizontalAlignment="Stretch"
-            VerticalAlignment="Stretch"
-            RowSpacing="10">
-            <Grid.RowDefinitions>
-              <RowDefinition Height="Auto" />
-              <RowDefinition Height="Auto" />
-              <RowDefinition Height="*" />
-              <RowDefinition Height="Auto" />
-            </Grid.RowDefinitions>
-            <Grid.ColumnDefinitions>
-              <ColumnDefinition Width="*" />
-            </Grid.ColumnDefinitions>
+            VerticalAlignment="Stretch">
+            <StackPanel Spacing="4">
+              <TextBlock FontWeight="SemiBold" Text="Pièces jointes" />
+              <ItemsControl ItemsSource="{Binding DraftAttachments}">
+                <ItemsControl.ItemTemplate>
+                  <DataTemplate>
+                    <TextBlock Text="{Binding FileName}" />
+                  </DataTemplate>
+                </ItemsControl.ItemTemplate>
+              </ItemsControl>
+            </StackPanel>
+          </Border>
 
-            <TextBlock
-              Grid.Row="0"
-              FontWeight="SemiBold"
-              Text="Post detail" />
-            <TextBox
-              x:Name="DraftTitleTextBox"
-              Grid.Row="1"
-              PlaceholderText="Title"
-              Text="{Binding DraftTitle, Mode=TwoWay}" />
+          <postitControls:StatusBar Grid.Row="4" DataContext="{Binding ActionStatus}" x:Name="StatusBar" />
 
-
-            <AvaloniaEdit:TextEditor
-              x:Name="DraftArticleTextEditor"
-              Grid.Row="2"
-              VerticalAlignment="Stretch"
-              Document="{Binding DraftArticleDocument, Mode=TwoWay}"
-              FontFamily="Cascadia Code,Consolas,Menlo,Monospace"
-              ShowLineNumbers="True"
-              WordWrap="True"
-              BorderThickness="1"
-              BorderBrush="LightGray"
-              CornerRadius="5"
-              Padding="5,5,5,15"
-              HorizontalScrollBarVisibility="Disabled"
-              TextInputOptions.Multiline="True"
-              TextInputOptions.ReturnKeyType="Default"
-              />
-
-            <Border x:Name="AttachmentsBorder"
-              Grid.Row="3"
-              Padding="8"
-              BorderBrush="LightGray"
-              BorderThickness="1"
-              HorizontalAlignment="Stretch"
-              VerticalAlignment="Stretch">
-              <StackPanel Spacing="4">
-                <TextBlock FontWeight="SemiBold" Text="Pièces jointes" />
-                <ItemsControl ItemsSource="{Binding DraftAttachments}">
-                  <ItemsControl.ItemTemplate>
-                    <DataTemplate>
-                      <TextBlock Text="{Binding FileName}" />
-                    </DataTemplate>
-                  </ItemsControl.ItemTemplate>
-                </ItemsControl>
-              </StackPanel>
-            </Border>
-
-            <postitControls:StatusBar Grid.Row="4" DataContext="{Binding ActionStatus}" x:Name="StatusBar" />
-
-          </Grid>
-        </Border>
+        </Grid>
       </Grid>
     </StackPanel>
-  </ScrollViewer>
 </ContentPage>