Thank you for writing.
When the user is filtering, the filter row is current and this is why the index is -1. You can check if the user is editing data row with the following code:
sender, Telerik.WinControls.UI.GridViewCellEventArgs e)
value = radGridView1.CurrentRow.Cells.Value.ToString();
Please let me know if there is something else I can help you with.
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