The case is that initially there are still not items loaded, consequently the SelectedItem cannot be connected with the GridViewRow corresponding to the particular item. You could subscribe for the DataLoaded event of RadGridView and select the desired item as soon as the data in the control is loaded.
You will be able to assign it once it is actually loaded.
For example, you can assure the item is already available with the following code:
sender, System.EventArgs e)
var item4 = RadGridView1.Items;
RadGridView1.SelectedItem = item4;
Let me know how this works for you.
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