In some scenarios it is required to load thousands of items in a ComboBox. Since by default the control creates RadComboBoxItem containers for each data item, it might take some time to open the drop-down. To resolve the problem you only need to change the RadComboBox ItemsPanel with VirtualizingStackPanel:

<telerikInput:RadComboBox> <telerikInput:RadComboBox.ItemsPanel> <ItemsPanelTemplate> <VirtualizingStackPanel /> </ItemsPanelTemplate> </telerikInput:RadComboBox.ItemsPanel> </telerikInput:RadComboBox>


thus making the drop-down to open instantly.

Attached is a simple application that loads 1000 items in two RadComboBox controls, one virtualized, the other – not virtualized. The difference between the two controls is visible and becomes much larger if you create 100,000 items!

I hope this helps.

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