feat: Add runtime page size changes

Author: DerekGooding

SimpleDataGrid.Example/MainViewModel.cs

@@ -7,6 +7,7 @@ namespace SimpleDataGrid.Example;
 public class MainViewModel
 {
     public PagedCollection<Person> People { get; }
+    public List<int> PageSizes { get; } = [10, 25, 50, 100];
 
     public MainViewModel()
     {

SimpleDataGrid.Example/MainWindow.xaml

@@ -72,6 +72,7 @@
             <TextBlock Text="Go to page:" VerticalAlignment="Center" Margin="5,0,0,0"/>
             <TextBox x:Name="PageTextBox" Width="30" Margin="5,0,0,0"/>
             <Button Content="Go" Click="GoToPageButton_Click" Margin="5,0,0,0"/>
+            <ComboBox Margin="10,0,0,0" ItemsSource="{Binding PageSizes}" SelectedItem="{Binding People.PageSize}"/>
             <TextBlock VerticalAlignment="Center" Margin="10,0,0,0">
                 <TextBlock.Text>
                     <MultiBinding Converter="{StaticResource ItemCountConverter}">

SimpleDataGrid/Pagination/PagedCollection.cs

@@ -10,12 +10,21 @@ namespace SimpleDataGrid.Pagination;
 /// <typeparam name="T">The type of items in the collection.</typeparam>
 public class PagedCollection<T> : IPagedCollection, INotifyPropertyChanged
 {
-    private readonly int _pageSize;
+    private int _pageSize;
     private int _currentPage;
+
+    /// <summary>
+    /// Occurs when the page size changes.
+    /// </summary>
+    public event EventHandler? PageSizeChanged;
     /// <summary>
-    /// Gets the number of items to display per page.
+    /// Gets or sets the number of items to display per page.
     /// </summary>
-    public int PageSize => _pageSize;
+    public int PageSize
+    {
+        get => _pageSize;
+        set => SetPageSize(value);
+    }
     private IReadOnlyList<T> _source = [];
     private IReadOnlyList<T> _filtered = [];
 
@@ -295,6 +304,22 @@ public void GoToLastPage()
         GoToPage(TotalPages);
     }
 
+    /// <summary>
+    /// Sets the number of items to display per page.
+    /// </summary>
+    /// <param name="newSize">The new page size.</param>
+    public void SetPageSize(int newSize)
+    {
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(newSize);
+
+        var oldFirstItemIndex = _currentPage * _pageSize;
+        _pageSize = newSize;
+        _currentPage = oldFirstItemIndex / _pageSize;
+
+        RaiseAllChanged();
+        PageSizeChanged?.Invoke(this, EventArgs.Empty);
+    }
+
     private void RaiseAllChanged()
     {
         OnPropertyChanged(nameof(CurrentPageItems));