10.Dropdown

 var _current_selected_item="Rupees";

 DropdownButton<String>(items: _currencies.map((String dropdown){
                return DropdownMenuItem<String>(
                  value: dropdown,
                  child: Text(dropdown),
                );
              }).toList(),onChanged:(String newSelectedText)
              {
                setState(() {
                  this._current_selected_item=newSelectedText;

                });


              },
              value: this._current_selected_item,),