HomeScreen - appBar bottom Dropdown

home.dart

AppBar(
  title: Text('Holden'),
  elevation: 0,
  shape: RoundedRectangleBorder(
    borderRadius: BorderRadius.only(
      bottomRight: Radius.circular(50),
      bottomLeft: Radius.circular(50),
    ),
  ),
  centerTitle: true,
  bottom: homeProvider.xlsxFilePath != null
      ? PreferredSize(
          preferredSize: Size.fromHeight(60),
          child: Container(
            margin: EdgeInsets.symmetric(horizontal: 60),
            child: DropdownButtonFormField(
              value: homeProvider.xlsxFileSelectedTable,
              onChanged: (newXlsxFileSelectedTable) {
                homeProvider.xlsxFileSelectedTable =
                    newXlsxFileSelectedTable;
              },
              items: [
                ...homeProvider.xlsxFileTables.keys.map(
                  (table) => DropdownMenuItem(
                    child: Text(table),
                    value: table,
                  ),
                ),
              ],
            ),
          ),
        )
      : PreferredSize(
          child: Container(),
          preferredSize: Size.fromHeight(0),
        ),
)