title: type 'List<dynamic>' is not a subtype of type 'List<DropdownMenuItem<String>>'
body: <p>Im working on a flutter project where i pass an array of objects (List> array) to the stream-builder from my bloc. If i print the object it prints nicely, but when i try to map them out in the DropdownMenuItem, it throws me the mentioned error. Hence, if i create a dummy array in the same format within the class and access it i do not get the error. not sure what am I missing here, code as bellow.</p>
  
  <pre><code>          StreamBuilder(
            stream: _bLoc.getJsonArray,
            builder: (context, snapshot) {
              return snapshot.hasData
                  ? new Container(
                      width: 150,
                      color: Theme.of(context).primaryColor,
                      child: new DropdownButton&lt;String&gt;(
                        items: snapshot.data.map((value) =&gt;
                           new DropdownMenuItem&lt;String&gt;(
                            value: value["distance"],
                            child: new Text(value["distance"]),
                          )
                        ).toList(),
                        onChanged: (_) {},
                      ),
                    )
                  : Container();
            }),
  </code></pre>
  
  <p>my json structure as bellow.</p>
  
  <pre><code> [
    {"distance": "12km","price": "200LKR",},
    {"distance": "2km","price": "100LKR",},
    {"distance": "132km","price": "340LKR",}
   ]
  </code></pre>