Flutter：如何使用 ListTile 作为子项创建 DropdownMenuItem

Question

I want to create a DropDownButton where the DropDownMenuItem has a ListTile() as child, instead of an usual Text() widget. There is a similar question asked here , but unfortunately the answer doesnn't seem to work.

Here is my code:

class _MyHomePageState extends State<MyHomePage> {
  String choice = 'Item 1';

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Card(
        child: DropdownButton(
          value: choice,
          items: stringItems.map<DropdownMenuItem<String>>((String value) {
            return DropdownMenuItem<String>(
              value: value,
              child: getListTile(value),
              // child: Text(value),
            );
          }).toList(),
          onChanged: (String newValue) {
            setState(() {
              choice = newValue;
            });
          }
        )
      ),
    );
  }

  Widget getListTile(String value) {
    return ListTile(
      leading: Text('FooBar'),
      title: Text(value),
      trailing: Icon(Icons.euro_symbol),
    );
  }

  List<String> stringItems = ['Item 1', 'Item 2', 'Item 3', 'Item 4'];
}

The following Exception is thrown:

The following assertion was thrown during performLayout():
BoxConstraints forces an infinite width.
The offending constraints were:
BoxConstraints (w=Infinity, 0.0<=h<=48.0)
The relevant error-causing widget was:
ListTile

I have done some research about this exception, but all I have found were articles/tutorials dealing with columns and rows. What exactly is the problem? (As far as I understand it, the ListTile will stretch in width to infinity).

Solutions I have tried so far:

1. I tried to set the "width" of the ListTile to a specific value, but the ListTile doesn't have a property "width".

2. I have wrapped the ListTile-Widget in an Expanded-Widget. But this didn't work too.

Is there a solution?

Thanks in advance!

Answer 1

The ListTile has no constraints and will try to use as much space as possible. If you wrap your ListTile with a Container with fixed height and width , you will no longer have a problem:

Widget getListTile(String value) {
  return Container(
    height: 60,
    width: 100,
    child: ListTile(
      leading: Text('FooBar'),
      title: Text(value),
      trailing: Icon(Icons.euro_symbol),
    ),
  );
}