how to open drawer from another widget class in flutter code example

Example: add a drawer flutter

Drawer(
  // Add a ListView to the drawer. This ensures the user can scroll
  // through the options in the drawer if there isn't enough vertical
  // space to fit everything.
  child: ListView(
    // Important: Remove any padding from the ListView.
    padding: EdgeInsets.zero,
    children: <Widget>[
      DrawerHeader(
        decoration: BoxDecoration(
          color: Colors.blue,
        ),
        child: Text('Drawer Header'),
      ),
      ListTile(
        title: Text('Item 1'),
        onTap: () {
          // Update the state of the app.
          // ...
        },
      ),
      ListTile(
        title: Text('Item 2'),
        onTap: () {
          // Update the state of the app.
          // ...
        },
      ),
    ],
  ),
);