Flutter - Auto size AlertDialog to fit list content

Wrap your Container inside a Column, in the content paramenter, inside of it, set the mainAxisSize.min, in Column property

I know it's quite late, but have you tried this?

Column(
    mainAxisSize: MainAxisSize.min,
    children: <Widget>[
       Container(
         child: ListView.builder(
           shrinkWrap: true,
           ...
         ),
       )
    ],
);

Don't set mainAxisSize.min in your Column otherwise you might run into overflow error if the content is longer than the viewport. To solve this issue, use either of the approaches.

1. Set scrollable: true in AlertDialog:

AlertDialog(
  scrollable: true, // <-- Set it to true
  content: Column(
    children: [...],
  ),
)

2. Wrap Column in SingleChildScrollView:

AlertDialog(
  content: SingleChildScrollView( 
    child: Column(
      children: [...],
    ),
  ),
)

3. Set shrinkWrap: true in ListView:

AlertDialog(
  content: SizedBox(
    width: double.maxFinite,
    child: ListView(
      shrinkWrap: true, // <-- Set this to true
      children: [...],
    ),
  ),
)

I have a similar problem. I fixed it by adding: scrollable: true in AlertDialog

Updated Code will be :

 createDialog() {
    fetchCities().then((response) {
      showDialog(
          context: context,
          builder: (BuildContext context) {
            return AlertDialog(
              scrollable: true,
              title: Text('Wybierz miasto'),
              content: Container(
                height: 200.0,
                width: 400.0,
                child: ListView.builder(
                  shrinkWrap: true,
                  itemCount: response.length,
                  itemBuilder: (BuildContext context, int index) {
                    return ListTile(
                      title: Text(response[index].name),
                      onTap: () => citySelected(response[index].id),
                    );
                  },
                ),
              ),
            );
          }
      );
    });
  }