RadzenDropDown: LoadData called twice on filter and once again on blur/focus

[k-Sacr]

Describe the bug
When filtering in RadzenDropDown, the data loading method (LoadData) is called twice for a single Filter input change. Based on the logs it seems the calls are executed on different threads.
Additionally, when the filter input loses focus (blur), the data loading method is triggered again even though the filter value did not change. This seems unintended.

To Reproduce
Steps to reproduce the behavior:

1. Open a page example with /dropdown-filtering bound via LoadData.
2. Set a breakpoint in the method that is called when loading data.
3. Type a value in a filter input.
4. Observe in the logs that LoadData is called twice (in different threads).
5. Click outside of the filter input (blur event).
6. Observe that LoadData is called again unexpectedly.

Expected behavior

• LoadData should be called only once per filter change.
• Losing focus from the filter input should not trigger LoadData unless explicitly configured.

Screenshots / Video

Code_2025-09-25_18-59-17.mp4

Attached video demonstrates:

• Double LoadData calls after typing.
• Additional LoadData call after filter input loses focus.

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Chrome 129
• Radzen Blazor DataGrid version: 7.4.1

Additional context
It would be helpful to introduce a flag or configuration option to suppress the LoadData call on blur of filter inputs.

[joriverm]

just to see if this is what i had noticed last week, is it being called with the same filter/arguments both times?

[joriverm]

looks like its called twice. once from OnFilter and once from OnKeyPress
and #2302 happens on the execution of OnFilter, curious.

[joriverm]

@k-Sacr / @enchev : this seems to happen because of the OnKeyDown event handler + the OnChange event handler in the search input field : https://github.com/radzenhq/radzen-blazor/blob/master/Radzen.Blazor/RadzenDropDown.razor#L152-L155

i was playing around and i think adding a debounce to OnFilter may fix this, but i dont feel good with that change. any recommendations? is OnChange even needed since its now basically triggering on key input and on focus loss/blur? removing the onchange, and therefor the dubbel trigger, does help it speed up though.

ill be testing some stuff locally together with my fix for #2302

[joriverm]

thanks for the merge/fix @enchev ^^