Thank you for the question.
In order to optimize the performance, you should read the images from the files in advance and put them into an ImageList. Then, when you start creating and adding RadComboBoxItems, use this ImageList to get the necessary images. I am attaching a sample project that demonstrates this approach.
You can get another performance optimization by using BeginUpdate/EndUpdate
. You can find an example of calling these methods in our Quick State Framework examples, section Editors >> RadComboBox >> Loading items
I hope this helps. If you have additional questions, feel free to contact me.
All the best,
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.