SelectAll checkboxes on checking one - Flutter

I need to check all checkboxes, on check of one.

Main Code dynamically creates cards with checkboxes in them

          future: getUsers(),
          builder: (BuildContext context, AsyncSnapshot snapshot){
            if(snapshot.data == null){
              return Container(
                child: Center(
                  child: CircularProgressIndicator(),
                ),
              );
            }else{
              return ListView.builder(
                shrinkWrap: true,
                itemCount: snapshot.data.length,
                itemBuilder: (BuildContext context, int index) {
                  ServiceProvider serviceProvider = snapshot.data[index];
                  return new Card(
                    shape: selectedName.contains(index)
                        ? new RoundedRectangleBorder(
                        side: new BorderSide(color: Colors.blue, width: 2.0),
                        borderRadius: BorderRadius.circular(4.0))
                        : new RoundedRectangleBorder(
                        side: new BorderSide(color: Colors.white, width: 2.0),
                        borderRadius: BorderRadius.circular(4.0)),
                    child: new Padding(
                      padding: const EdgeInsets.all(5.0),
                      child: new Column(
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: <Widget>[
                          new Text(serviceProvider.name, style: TextStyle(fontSize: 20, height: 1.5)),
                          new Text(serviceProvider.serviceType, style: TextStyle(fontSize: 15, height: 1.5),),
                          new Text(serviceProvider.phoneNumber, style: TextStyle(fontSize: 15, height: 1.5),),
                          new Text(serviceProvider.address, style: TextStyle(fontSize: 15, height: 1.5),),
                          new Text(serviceProvider.location, style: TextStyle(fontSize: 15, height: 1.5),),
                          new Text(serviceProvider.emailAddress, style: TextStyle(fontSize: 15, height: 1.5),),
                          Container(
                            child: ButtonBar(
                              children: <Widget>[
                                new Checkbox(
                                    value: selectedName.contains(serviceProvider.name),
                                    onChanged: (value) {
                                      setState(() {
                                        if(value){
                                          selectedName.add(serviceProvider.name);
                                        }else{
                                          selectedName.remove(serviceProvider.name);
                                        }
                                      });
//                                      selectedName.add(serviceProvider.name);
                                      print(selectedName);
                                    }),

Now, I have a persistentFooterButton widget that has a single checkbox. On checking this checkbox, I want the main code checkboxes to get selected.

PersistentFooterButtons widget

Checkbox(
            value: selected,
            onChanged: (value) {
              setState(() {
                if(value){
                  selectedName.clear();
                  selectedName.addAll(Iterable<int>.generate(snapshotData.length).toList());
                }else{
                  selectedName.clear();
                }
              });
              print(selectedName);
            }),

How can I got about doing this?