Hi Jalil,
Thank you using syncfusion product,
We have analyzed your query at our end. We have already provide the sample for on demand loading of data in GridControl. Please refer the sample from below mentioned sample location. In this sample we have used the QueryCellInfoEvent to assign the values for visible rows. QuerRowCount and QueryColCount event used to assign the number of rows and columns for virtual grid. Please refer the below KB and UG links.
Sample location: <Installed location>\Syncfusion\EssentialStudio\<Version Number>\Windows\Grid.Windows\Samples\Virtual Grid\Virtual Grid Demo
Regards,
Mohanraj G.