feat: Add empty state support

Author: DerekGooding

SimpleDataGrid.Example/MainWindow.xaml

@@ -11,6 +11,7 @@
         Title="MainWindow" Height="450" Width="800">
     <Window.Resources>
         <converters:ItemCountConverter x:Key="ItemCountConverter"/>
+        <BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
     </Window.Resources>
     <Window.DataContext>
         <local:MainViewModel />
@@ -56,6 +57,13 @@
 
         <controls:PagedDataGrid x:Name="PagedDataGrid" Grid.Row="1" PagedSource="{Binding People}" AutoGenerateColumns="True" />
 
+        <Grid Grid.Row="1" Background="#AAFFFFFF" Visibility="{Binding People.IsEmpty, Converter={StaticResource BooleanToVisibilityConverter}}">
+            <StackPanel VerticalAlignment="Center" HorizontalAlignment="Center">
+                <TextBlock Text="No items found." FontSize="24" FontWeight="Bold" Margin="0,0,0,10"/>
+                <TextBlock Text="Try clearing your filters or search terms." FontSize="14" TextAlignment="Center"/>
+            </StackPanel>
+        </Grid>
+
         <StackPanel Grid.Row="2" Orientation="Horizontal" HorizontalAlignment="Center">
             <Button Content="First" Click="FirstButton_Click" Margin="5" IsEnabled="{Binding People.HasPrevious}"/>
             <Button Content="Previous" Click="PreviousButton_Click" Margin="5" IsEnabled="{Binding People.HasPrevious}"/>

SimpleDataGrid/Pagination/PagedCollection.cs

@@ -248,6 +248,21 @@ private static string WildcardToRegex(string pattern)
     /// </summary>
     public int TotalItems => _filtered.Count;
 
+    /// <summary>
+    /// Gets a value indicating whether the filtered collection is empty.
+    /// </summary>
+    public bool IsEmpty => _filtered.Count == 0;
+
+    /// <summary>
+    /// Gets a value indicating whether the filtered collection has any items.
+    /// </summary>
+    public bool HasItems => _filtered.Count > 0;
+
+    /// <summary>
+    /// Gets a value indicating whether the original source collection is empty.
+    /// </summary>
+    public bool IsSourceEmpty => _source.Count == 0;
+
     /// <summary>
     /// Gets a value indicating whether there is a next page.
     /// </summary>
@@ -347,6 +362,9 @@ private void RaiseAllChanged()
         OnPropertyChanged(nameof(TotalPages));
         OnPropertyChanged(nameof(HasNext));
         OnPropertyChanged(nameof(HasPrevious));
+        OnPropertyChanged(nameof(IsEmpty));
+        OnPropertyChanged(nameof(HasItems));
+        OnPropertyChanged(nameof(IsSourceEmpty));
     }
 
     /// <summary>