There is significant latency when a user has many images in a list or dropdown list, particularly those with sub-choices that also have images.  Because of this, we tried implementing design-time templates to allow lazy loading of images for RadComboBox.  While implementing a solution is possible, it was much more complicated than expected.

We have previuisly raised a feature request for simular controls that was fixed (Thanks for that) but our topp prioority component is The combobox. see Allow lazy loading of images with design-time templates for ListBox and ComboBox

During the discussion a few questions was rasied from telerik:

Currently, the ComboBox has the Load on Demand functionality which focuses on loading items as needed, but it does not specifically address lazy loading of images inside the templates. Before proceeding further, I’d like to confirm your current setup to suggest the best approach:

• Are you using server-side or client-side data binding with RadComboBox?
• Are you using design-time templates or injecting templates dynamically?
• How are images currently loaded in your ComboBox items?
• Is your main concern the initial load time, scrolling performance, or something else?

Reasons (Hope it makes sense)

• Only server-side databinding (with both controls).

• We are using both ItemTemplate with custom images (where we then control lazy loading ourselves) and ImageUrl where we lose this possibility and have issues. We also dynamically load custom controls (ITemplate) in a few places.