title: Evaluation of this constant expression throws an expression
body: <p>My dart analysis is showing the following error  in the code :</p>
  
  <pre><code>error: Evaluation of this constant expression throws an exception. 
          (const_eval_throws_exception at [laundry] 
          lib\pick_drop_ui\pages\works.dart:97) error: Arguments of a constant creation must be constant expressions. 
          (const_with_non_constant_argument at [laundry] 
          lib\pick_drop_ui\pages\works.dart:98) error: Arguments of a constant creation must be constant expressions. 
          (const_with_non_constant_argument at [laundry] 
          lib\pick_drop_ui\pages\works.dart:104) error: Evaluation of this constant expression throws an exception. 
         (const_eval_throws_exception at [laundry] 
         lib\pick_drop_ui\pages\works.dart:104)
  </code></pre>
  
  <p>in the following code :</p>
  
  <pre><code>import 'package:flutter/foundation.dart';
  import 'package:flutter/material.dart';
  
  class work extends StatefulWidget {
    @override
    _workState createState() =&gt; _workState();
  }
  
  class _workState extends State&lt;work&gt; {
  
    var workdata;                        //Variable to get the snapshort of the works available in the firestore
  
    @override
    void initState() {
      // TODO: implement initState
      super.initState();
      print("Called work");
      setState(() {
        workdata = getData();
      });
    }
  
  
    getworkdetails(){
      if(workdata != null){
        return StreamBuilder(
          stream: workdata,
          builder: (context,snapshot){
            if(snapshot.data != null){
            return ListView.builder(
              shrinkWrap: true,
              itemCount: snapshot.data.documents.length,
              itemBuilder: (context,i){
                return workcards(snapshot.data.documents[i].data['Name of customer'],snapshot.data.documents[i].data['Address']);
              },
            );
            }else{
              return Text("Malfunction");
            }
          },
        );
      }else{
        print("getting workdata");
      }
    }
  
  
  
  
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        appBar: AppBar(
          title: Text("Jobs Assigned"),
        ),
  
        body: getworkdetails(),
      );
    }
  }
  
  
  getData() {
    return Firestore.instance.collection('Jobs').snapshots();
  }
  
  
  class workcards extends StatelessWidget{
  
    final  name;
    final  address;
  
    workcards(this.name,this.address);
  
  
    @override
    Widget build(BuildContext context) {
      // TODO: implement build
      return Card(
        color: Colors.blueGrey[50],
        child: InkWell(
          splashColor: Colors.blue[100].withAlpha(100),
          onTap: () {
          },
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: &lt;Widget&gt;[
              const ListTile(
                leading: Icon(Icons.view_module),
                // Error: invalid constant value
                title: Text(
                  name,
                  style: TextStyle(
                    fontWeight: FontWeight.w600,
                    letterSpacing: .5,
                  ),
                ),
                // Error: invalid constant value
                subtitle: Text(address),
              ),
              ButtonBar(
                children: &lt;Widget&gt;[
                  RaisedButton(
                    child: const Text('OPEN'),
                    onPressed: () {/* ... */},
                    focusElevation: 10,
                  ),
                  RaisedButton(
                    child: const Text('SHARE'),
                    onPressed: () {/* ... */},
                    focusElevation: 20,
                  ),
                ],
              ),
            ],
          ),
        ),
      );
    }
  }
  
  </code></pre>