By default, you can only access the Text value of AutoComplete in the Controller page on post action. In order to get the Key value of the selected item from AutoComplete in the Controller page, you have to pass the Key value through client-side events.
The Key value of the selected item is obtained from OnValueChange event using the event arguments. You can fetch the corresponding selected items Key value in the client-side script, using the event argument property _dataIdItem or the method get_DataId().
From the client-side, button-click event trigger, the AJAX post to pass the variable holds the Key value. Now the value stored in the OnValueChange event is passed to controller using AJAX post where you can get the Key Value of the selected AutoComplete item. Refer the following code example.
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