firebase - Flutter - Fetch Data from firestore and display it in a dropdown list

Question

I'm trying to fetch data from firestore and display it in a dropdown menu. I tried declaring the list like the following: ? List makes = [''] but I can’t view the data until I click on another field and the dropdown gets populated at multiple occasions. I have it in a method because eventually, I would like to create a second dropdown where there’s a condition in the database query.

ex. If Toyota is selected display all the models for that particular make.

new StreamBuilder<QuerySnapshot>(
      stream: Firestore.instance.collection("makesModels").snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) return new Text("Please wait");
        return new DropdownButton(
          items: snapshot.data.documents.map((DocumentSnapshot document) {
            return DropdownMenuItem(
                value: document.data["make"],
                child: new Text(document.data["make"]));
          }).toList(),
          value: category,
          onChanged: (value) {
            setState(() {
              category = value;
            });
          },
          hint: new Text("Makes"),
          style: TextStyle(color: Colors.black),
        );
      }),
      new StreamBuilder<QuerySnapshot>(
      stream: Firestore.instance.collection("makesModels").where('make', isEqualTo: category).snapshots(),
      builder: (context, snapshot) {

        if (!snapshot.hasData) return new Text("Please wait");
        return new DropdownButton(
          items: snapshot.data.documents.map((DocumentSnapshot document) { 
            for(int i = 0; i < document.data['models'].length; i++){

              print(document.data['models'][i]);
              return new DropdownMenuItem(
              value: document.data['models'][i],
                child: new Text(document.data['models'][i].toString()),
              );
            }   

            }).toList(),
          value: models,
          onChanged: (value) {
            print(value);

            setState(() {
              models = value;
            });
          },
          hint: new Text("Models"),
          style: TextStyle(color: Colors.black),
        );
      }),

Answer 1

Waitting for answers