How to pass objects from datagrid to reference selector?

Associated MLS's (reference selector) is selected and clicked add button, it is navigating to a popup to select MLS(datagrid). Select is here default button and if MLS records are there select operation is working fine but if MLS is empty and i try to select, it is closing without a warning message. So tried with customized select button. The difficulty i find here is, the selected MLS list should be passed to associated MLS object, that cannot be done in customized button. The datagrid object should be passed to reference selector object. Can you suggest any ideas to fix this issue? How to add warning message to default button?
1 answers

Use a microflow to open the select page. Before opening the page do a retrieve to check if selections are available, if not close the screen with message to user.