Fix #4676 for V5 (#4679)

Author: vnbaaij

src/Core/Components/DataGrid/FluentDataGrid.razor.cs

@@ -57,6 +57,7 @@ public partial class FluentDataGrid<TGridItem> : FluentComponentBase, IHandleEve
     private bool? _lastVirtualizationMode;
     private GridItemsProvider<TGridItem>? _lastAssignedItemsProvider;
     private CancellationTokenSource? _pendingDataLoadCancellationTokenSource;
+    private bool _isFirstVirtualizeProviderCall = true;
     private Exception? _lastError;
     private GridItemsProviderRequest<TGridItem>? _lastRequest;
     private bool _forceRefreshData;
@@ -443,7 +444,7 @@ public FluentDataGrid(LibraryConfiguration configuration) : base(configuration)
 
     // Returns Loading if set (controlled). If not controlled,
     // we assume the grid is loading until the next data load completes
-    internal bool EffectiveLoadingValue => Loading ?? ItemsProvider is not null;
+    internal bool EffectiveLoadingValue => Loading ?? (ItemsProvider is not null);
 
     /// <summary>
     /// Indicates whether the grid is currently sorted ascending.
@@ -796,7 +797,7 @@ public async Task RemoveSortByColumnAsync(ColumnBase<TGridItem> column)
                 await OnSortChanged.InvokeAsync(new()
                 {
                     Column = _sortByColumn,
-                    SortByAscending = _sortByAscending
+                    SortByAscending = _sortByAscending,
                 });
             }
 
@@ -994,11 +995,16 @@ private async Task RefreshDataCoreAsync()
     private async ValueTask<ItemsProviderResult<(int, TGridItem)>> ProvideVirtualizedItemsAsync(ItemsProviderRequest request)
     {
         _lastRefreshedPaginationState = Pagination;
+        // Debounce the requests (except on first call). This eliminates a lot of redundant queries at the cost of slight lag after interactions.
+        if (_isFirstVirtualizeProviderCall)
+        {
+            _isFirstVirtualizeProviderCall = false;
+        }
+        else
+        {
+            await Task.Delay(20);
+        }
 
-        // Debounce the requests. This eliminates a lot of redundant queries at the cost of slight lag after interactions.
-        // TODO: Consider making this configurable, or smarter (e.g., doesn't delay on first call in a batch, then the amount
-        // of delay increases if you rapidly issue repeated requests, such as when scrolling a long way)
-        await Task.Delay(20);
         if (request.CancellationToken.IsCancellationRequested)
         {
             return default;

tests/Core/Components/DataGrid/FluentDataGridTests.razor

@@ -309,7 +309,7 @@
 
         Assert.NotEmpty(rows); // Asserting that there are rows present
         //Assert.Equal(101, rows.Count);  //In bUnit the actual height of the grid can't be determined, so we just check that at least one row is rendered.
-        Assert.Single(rows);  //In bUnit the actual height of the grid can't be determined, so we just check that at least one row is rendered.
+        Assert.Equal(21, rows.Count);  //In bUnit the actual height of the grid can't be determined, so we just check that at least one row is rendered.
 
     }