Disable Control Render

Question

In WPF I have a control to load titles but the control is very slow to render on screen. I have been told that I can use BeginInit() of the control to add the items and not render them. How do I use it if the control has already been initialized and is displayed on screen? Can you give an example?

I've tried this and the control still loads items on screen:

((System.ComponentModel.ISupportInitialize)Control).BeginInit(); 

// Add Items.

((System.ComponentModel.ISupportInitialize)Control).EndInit(); 

Answer 1

Hi @zequion , Welcome to Microsoft Q&A,

In WPF, the main purpose of BeginInit() and EndInit() is to provide bulk initialization for controls to reduce unnecessary relayouts and repaints when the controls load. However, using only BeginInit() and EndInit() does not significantly improve the loading performance of controls that are already initialized and displayed on the screen, especially when adding a large number of items.

If your control is an ItemsControl (such as a ListBox or DataGrid), you can enable virtualization to reduce the rendering overhead. Virtualization creates and renders only the visible items instead of loading all items.

Example: For ListBox, you can enable virtualization:

<ListBox VirtualizingStackPanel.IsVirtualizing="True"
VirtualizingStackPanel.VirtualizationMode="Recycling">
<!-- Items -->
</ListBox>

If you are adding items to a data-bound control, you can use the CollectionView's DeferRefresh() method to defer UI updates until all items are added.

var collectionView = CollectionViewSource.GetDefaultView(myControl.ItemsSource);
using (collectionView.DeferRefresh())
{
// Add items in batches
myControl.ItemsSource = GetLargeData();
}

If you are adding a large number of items, asynchronous loading can prevent the UI thread from being blocked, thus avoiding UI lags.

Best Regards,

Jiale

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