I am getting this runtime error although If I click the back button, then the screen gets navigated to the route I'm trying to redirect but before that this error screen always pops up.

Here's the code snippet:

 body: Container(
    child: FutureBuilder<DocumentSnapshot>(
    future: _service.categories.doc(args.id).get(),
       builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
        if (snapshot.hasError) {
          return Container();
        }

        if (snapshot.connectionState == ConnectionState.waiting) {
          return Center(child: CircularProgressIndicator(),);
        }

        var data = snapshot.data!['subCat'];
        return Container(
          child: ListView.builder(

            itemCount: data.length,
            itemBuilder: (BuildContext context, int index){

              return Padding(
                padding: const EdgeInsets.only(left: 8,right: 8),
                child: ListTile(
                  onTap: (){
                    //sub categories
                  },
                  title: Text(data[index],style: TextStyle(fontSize: 16),),
                ),
              );
            },
          ),
        );
      },
    ),
  ),

CodePudding user response：

You are handling error and loading state. Try checking data existence and then proceed of using this. In that case check data just after checking watting state.

if(!snapshot.hasData){
return Text("it doesnt Have any data");
}

I will encourage you not to use ! directly without checking null. In your case, it is on

var data = snapshot.data!['subCat'];

do

var data = snapshot.data?['subCat'];
if (data==null){
   return Text("subCat is empty");
}
///else move to list container

CodePudding user response：

It is because your "itemCount: data.length" does not have data to read. You can't invoke ".length" from a null instance.

Try to check whether your data is not null or whether it has values for the listView.builder can iterate.