A dataview is used to display a single object, and a datagrid is used to display a list of objects. You are getting an error because you arent defining what object to show in your dataview. To do this, you would have to pass an object as a parameter in a show page activity from a microflow, use a microflow as a datasource for the dataview and retrieve the object that you want to display, or if you want to the dataview to show the record that is selected in the datagrid, then you would use the "listen to widget" data source and select your datagrid.
Here is a link to a learning path that will be helpful.
Hope this helps!