type 'Null' is not a subtype of type 'List<Comic>' in type cast-CodePudding

I had some issue and cannot solve it when I followed Food App of EDMT Dev. I use Realtime database of Firebase to connect with my Flutter app but it returned Error "type 'Null' is not a subtype of type 'List' in type cast"

body: FutureBuilder(
    future: viewModel.displaygetComicList(),
    builder: (context, snapshot) {
      if(snapshot.connectionState == ConnectionState.waiting)
        return Center(child: CircularProgressIndicator(),);
      else
        {
          var lst = snapshot.data as List<Comic>;
          return ListView.builder(
            itemCount: lst!=null?lst.length:0,
            itemBuilder: (context, index) {
              return Text(lst[index].category);
            }
          );
          //return Center(child: Text('Load ok'),);

        }
    }),

Can anyone help me to solve this error? Thank you very much.

CodePudding user response：

Try this if you doubts feel free to ask

body: FutureBuilder(
future: viewModel.displaygetComicList(),
builder: (context, snapshot) {
  if(snapshot.connectionState == ConnectionState.waiting)
    return Center(child: CircularProgressIndicator(),);
  else if(snapshot.data !=null)          // check for null
    {
      var lst = snapshot.data as List<Comic>;
      return ListView.builder(
        itemCount: lst!=null?lst.length:0,
        itemBuilder: (context, index) {
          return Text(lst[index].category);
        }
      );
      //return Center(child: Text('Load ok'),);

    }
}),

CodePudding user response：

try to change

var lst = snapshot.data as List<Comic>;

var lst = snapshot.data as List<Comic>?;

This way you indicate that it's possible to be null. Your way you say it's definitely not null, but because it is it throws the error