top_bar_contents.dart

// Code for the Sign in button, present in the top bar

InkWell(
  child: userEmail == null
      ? Text(
          'Sign in',
          style: TextStyle(
            color: _isHovering[3] ? Colors.white : Colors.white70,
          ),
        )
      : Row(
          children: [
            CircleAvatar(
              radius: 15,
              backgroundImage: imageUrl != null
                  ? NetworkImage(imageUrl)
                  : null,
              child: imageUrl == null
                  ? Icon(Icons.account_circle, size: 30)
                  : Container(),
            ),
            Text(
              name ?? userEmail,
              style: TextStyle(
                color: _isHovering[3]
                    ? Colors.white
                    : Colors.white70,
              ),
            ),
            FlatButton(
              // ...
              onPressed: () {},
              child: Text(
                'Sign out',
                style: TextStyle(
                  fontSize: 14,
                  color: Colors.white,
                ),
              ),
            ),
          ],
        ),
),