Merge pull request #2963 from telerik/new-kb-kb-virtualqueryablecollectionview-gridview-itemsloading-manuall-e7685f444f4c41dda6f25692ec5b74c9

Added new kb article kb-virtualqueryablecollectionview-gridview-itemsloading-manuall

Author: martinivanoff

knowledge-base/kb-virtualqueryablecollectionview-gridview-itemsloading-manuall.md

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+---
+title: Load items in the ItemsLoading event of VirtualQueryableCollectionView manually When Used in RadGridView
+description: Handle the VirtualQueryableCollectionView.ItemsLoading event in RadGridView for WPF to load data on demand, suitable for large data sources.
+type: how-to
+page_title: How to Use VirtualQueryableCollectionView for On-Demand Data Loading in RadGridView
+slug: kb-virtualqueryablecollectionview-gridview-itemsloading-manuall
+tags: radgridview, wpf, virtualqueryablecollectionview, itemloading, on-demand data loading
+res_type: kb
+ticketid: 1666946
+---
+
+## Environment
+
+<table>
+<tbody>
+<tr>
+<td>Product</td>
+<td>RadGridView for WPF</td>
+</tr>
+<tr>
+<td>Version</td>
+<td>2024.3.821</td>
+</tr>
+</tbody>
+</table>
+
+## Description
+
+How to manually load data in `RadGridView` using the `VirtualQueryableCollectionView` and its `ItemsLoading` event, without working with `IQueryable` collection source. 
+
+This approach is meaningful when you don't want to load all your data in-memory, but fetch it in the `ItemsLoading` event handler.
+
+## Solution
+
+To do this, you can initialize the `VirtualQueryableCollectionView` with an empty collection source which later will be populated with data. 
+
+To adjust the total items count, set the `VirtualItemCount` property of the collection view.
+
+In the `ItemsLoading` event handler, you can manually fetch and add items in the collection view.
+
+#### __[C#] Setting up the VirtualQueryableCollectionView__
+{{region kb-virtualqueryablecollectionview-gridview-itemsloading-manuall-0}}
+	public MainWindow()
+	{
+		InitializeComponent();
+		
+		var vqcv = new VirtualQueryableCollectionView(new ObservableCollection<RowInfo>()) { LoadSize = 10, VirtualItemCount = 1000  };            
+		vqcv.ItemsLoading += VirtualQueryableCollectionView_ItemsLoading;	
+		this.gridView.ItemsSource = vqcv;
+	}
+
+	private void VirtualQueryableCollectionView_ItemsLoading(object? sender, VirtualQueryableCollectionViewItemsLoadingEventArgs e)
+	{
+		var vqcv = (VirtualQueryableCollectionView)sender;
+		var newItems = // fetch the new portion of items here
+		foreach (var item in newItems)
+		{
+			vqcv.Add(item);
+		}
+	}
+{{endregion}}
+
+