Flutter TabBar and TabBarView inside body of the application

tabList.map((Tab tab){
   _getPage(tab);
}).toList()

The piece above is from your provided code, you called _getPage(tab) in the map without a return statement. Simply make a slight change to this

tabList.map((Tab tab){
   return _getPage(tab);
}).toList()

Or

tabList.map((Tab tab) => _getPage(tab)).toList()

children: tabList.map((Tab tab){
         _getPage(tab);
         }).toList(),

Some how this above your logic will getting null children for TabBarView, So views of tabs are not visible, need to check for it.

OtherWise you can assign children of TabBarView manualy

children: <Widget>[
  OverView(),
  Workouts(),
],