How can we change the width/padding of a Flutter DropdownMenuItem in a Dropdown?

This feature has been added. See https://github.com/flutter/flutter/pull/14849

You can now wrap it in a ButtonTheme and set alignedDropdown to true.

return Container(
    width: 300.0,
    child: DropdownButtonHideUnderline(
      child: ButtonTheme(
        alignedDropdown: true,
          child: DropdownButton(
            value: name,
            items: listOfDropdownMenuItems,
            onChanged: onChanged,
            style: Theme.of(context).textTheme.title,
         ),
      ),
    ),
);

I solved this problem with changing isExpanded to true;

return Container(
    width: 300.0,
    child: DropdownButtonHideUnderline(
      child: DropdownButton(
        isExpanded: true,
        value: name,
        items: listOfDropdownMenuItems,
        onChanged: onChanged,
        style: Theme.of(context).textTheme.title,
      ),
    ),
);