From adfac7b69dbcdc79a676b04aaebe1db4d4d63b40 Mon Sep 17 00:00:00 2001
From: robloo <robloo@users.noreply.github.com>
Date: Thu, 2 Jun 2022 01:22:39 -0400
Subject: [PATCH] Implement tab selection validation and automatic width

---
 .../ColorView/ColorView.cs                    | 93 ++++++++++++++++++-
 .../Themes/Fluent/ColorView.xaml              | 23 +++--
 2 files changed, 105 insertions(+), 11 deletions(-)

diff --git a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
index 0363d9c182..96de734cc7 100644
--- a/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
+++ b/src/Avalonia.Controls.ColorPicker/ColorView/ColorView.cs
@@ -5,6 +5,7 @@ using Avalonia.Controls.Converters;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Primitives;
 using Avalonia.Media;
+using Avalonia.Threading;
 
 namespace Avalonia.Controls
 {
@@ -12,6 +13,7 @@ namespace Avalonia.Controls
     /// Presents a color for user editing using a spectrum, palette and component sliders.
     /// </summary>
     [TemplatePart("PART_HexTextBox", typeof(TextBox))]
+    [TemplatePart("PART_TabControl", typeof(TabControl))]
     public partial class ColorView : TemplatedControl
     {
         /// <summary>
@@ -20,7 +22,8 @@ namespace Avalonia.Controls
         public event EventHandler<ColorChangedEventArgs>? ColorChanged;
 
         // XAML template parts
-        private TextBox? _hexTextBox;
+        private TextBox?    _hexTextBox;
+        private TabControl? _tabControl;
 
         private ObservableCollection<Color> _customPaletteColors = new ObservableCollection<Color>();
         private ColorToHexConverter colorToHexConverter = new ColorToHexConverter();
@@ -31,7 +34,7 @@ namespace Avalonia.Controls
         /// </summary>
         public ColorView() : base()
         {
-            this.CustomPalette = new FluentColorPalette();
+            CustomPalette = new FluentColorPalette();
         }
 
         /// <summary>
@@ -66,6 +69,77 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <summary>
+        /// Validates the selected subview/tab taking into account the visibility of each subview/tab
+        /// as well as the current selection.
+        /// </summary>
+        private void ValidateSelectedTab()
+        {
+            if (_tabControl != null &&
+                _tabControl.Items != null)
+            {
+                // Determine if any item is visible
+                bool isAnyItemVisible = false;
+                foreach (var item in _tabControl.Items)
+                {
+                    if (item is Control control &&
+                        control.IsVisible)
+                    {
+                        isAnyItemVisible = true;
+                        break;
+                    }
+                }
+
+                if (isAnyItemVisible)
+                {
+                    object? selectedItem = null;
+
+                    if (_tabControl.SelectedItem == null &&
+                        _tabControl.ItemCount > 0)
+                    {
+                        // As a failsafe, forcefully select the first item
+                        foreach (var item in _tabControl.Items)
+                        {
+                            selectedItem = item;
+                            break;
+                        }
+                    }
+                    else
+                    {
+                        selectedItem = _tabControl.SelectedItem;
+                    }
+
+                    if (selectedItem is Control selectedControl &&
+                        selectedControl.IsVisible == false)
+                    {
+                        // Select the first visible item instead
+                        foreach (var item in _tabControl.Items)
+                        {
+                            if (item is Control control &&
+                                control.IsVisible)
+                            {
+                                selectedItem = item;
+                                break;
+                            }
+                        }
+                    }
+
+                    _tabControl.SelectedItem = selectedItem;
+                    _tabControl.IsVisible = true;
+                }
+                else
+                {
+                    // Special case when all items are hidden
+                    // If TabControl ever properly supports no selected item /
+                    // all items hidden this can be removed
+                    _tabControl.SelectedItem = null;
+                    _tabControl.IsVisible = false;
+                }
+            }
+
+            return;
+        }
+
         /// <inheritdoc/>
         protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
         {
@@ -76,6 +150,8 @@ namespace Avalonia.Controls
             }
 
             _hexTextBox = e.NameScope.Find<TextBox>("PART_HexTextBox");
+            _tabControl = e.NameScope.Find<TabControl>("PART_TabControl");
+
             SetColorToHexTextBox();
 
             if (_hexTextBox != null)
@@ -85,6 +161,7 @@ namespace Avalonia.Controls
             }
 
             base.OnApplyTemplate(e);
+            ValidateSelectedTab();
         }
 
         /// <inheritdoc/>
@@ -143,6 +220,18 @@ namespace Avalonia.Controls
                     }
                 }
             }
+            else if (change.Property == IsColorComponentsVisibleProperty ||
+                     change.Property == IsColorPaletteVisibleProperty ||
+                     change.Property == IsColorSpectrumVisibleProperty)
+            {
+                // When the property changed notification is received here the visibility
+                // of individual tab items has not yet been updated though the bindings.
+                // Therefore, the validation is delayed until after bindings update.
+                Dispatcher.UIThread.Post(() =>
+                {
+                    ValidateSelectedTab();
+                }, DispatcherPriority.Background);
+            }
 
             base.OnPropertyChanged(change);
         }
diff --git a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
index afc8682a66..420e3b2ae9 100644
--- a/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
+++ b/src/Avalonia.Controls.ColorPicker/Themes/Fluent/ColorView.xaml
@@ -109,22 +109,29 @@
                   BorderBrush="{ThemeResource DividerStrokeColorDefaultBrush}"
                   BorderThickness="0,1,0,0" />-->
 
-          <TabControl Grid.Row="0"
+          <TabControl x:Name="PART_TabControl"
+                      Grid.Row="0"
                       Height="338"
                       Width="350">
             <TabControl.Resources>
               <Thickness x:Key="TabItemMargin">0,0,0,0</Thickness>
             </TabControl.Resources>
             <TabControl.Styles>
-              <Style Selector="TabItem">
-                <Setter Property="Padding" Value="0" />
+              <Style Selector="TabControl">
+                <Setter Property="ItemsPanel">
+                  <Setter.Value>
+                    <ItemsPanelTemplate>
+                      <UniformGrid Columns="0"
+                                   Rows="1" />
+                    </ItemsPanelTemplate>
+                  </Setter.Value>
+                </Setter>
               </Style>
             </TabControl.Styles>
             <!-- Spectrum Tab -->
             <TabItem IsVisible="{TemplateBinding IsColorSpectrumVisible}">
               <TabItem.Header>
-                <Border Width="116"
-                        Height="{DynamicResource ColorViewTabStripHeight}">
+                <Border Height="{DynamicResource ColorViewTabStripHeight}">
                   <PathIcon Width="20"
                             Height="20"
                             Data="{DynamicResource ColorViewSpectrumIconGeometry}" />
@@ -181,8 +188,7 @@
             <!-- Palette Tab -->
             <TabItem IsVisible="{TemplateBinding IsColorPaletteVisible}">
               <TabItem.Header>
-                <Border Width="116"
-                        Height="{DynamicResource ColorViewTabStripHeight}">
+                <Border Height="{DynamicResource ColorViewTabStripHeight}">
                   <PathIcon Width="20"
                             Height="20"
                             Data="{DynamicResource ColorViewPaletteIconGeometry}" />
@@ -257,8 +263,7 @@
             <!-- Components Tab -->
             <TabItem IsVisible="{TemplateBinding IsColorComponentsVisible}">
               <TabItem.Header>
-                <Border Width="116"
-                        Height="{DynamicResource ColorViewTabStripHeight}">
+                <Border Height="{DynamicResource ColorViewTabStripHeight}">
                   <PathIcon Width="20"
                             Height="20"
                             Data="{DynamicResource ColorViewComponentsIconGeometry}" />