How to skip build in item builder gridview.builder Flutter Firebase Stream Builder

Question

I would like to delete something of firebase and when Streambuilder(gridview.builder) reach it index which gonna be null it ignore it and don't add any widget in that slot and keep it for others

this what it looks like

I want the empty space on the left and right to be gone and other widgets to take its place

Firebase Database Image

 classList(userUid) {
    print("user uid: $userUid");
    return StreamBuilder(
        stream: FirebaseDatabase.instance
            .reference()
            .child("user")
            .child(userUid)
            .child("classData")
            .onValue,
        builder: (BuildContext context, AsyncSnapshot<Event> snapshot) {
          if (snapshot.hasData) { //            Map<dynamic, dynamic> map = snapshot.data.snapshot.value; //            snapshot.data.snapshot.value.forEach((dynamic, v) => print(v["className"]));
            if (snapshot.data.snapshot.value != null) {
              return GridView.builder(
                gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                    crossAxisCount: 3),
                itemCount: snapshot.data.snapshot.value.toList().length,
                padding: EdgeInsets.all(2.0),
                scrollDirection: Axis.vertical,
                itemBuilder: (BuildContext context, int index) {
                  RandomColor _randomColor = RandomColor();

                  Color _color = _randomColor.randomColor(
                      colorBrightness: ColorBrightness.veryLight);

                  Color _color2 = _randomColor.randomColor(
                      colorBrightness: ColorBrightness.veryDark);
                  if (snapshot.data.snapshot.value.toList()[index] != null) {
                    return Container(
                      child: RaisedButton(
                        splashColor: _color2,
                        color: _color,
                        shape: SuperellipseShape(
                            borderRadius: BorderRadius.circular(90)),
                        onPressed: () {
                          Navigator.push(
                              context,
                              MaterialPageRoute(
                                  builder: (context) => ClassPage(
                                        className: snapshot.data.snapshot.value
                                            .toList()[index]["className"]
                                            .toString()
                                            .toUpperCase(),
                                        classSection: snapshot
                                            .data.snapshot.value
                                            .toList()[index]["classSection"]
                                            .toString()
                                            .toUpperCase(),
                                        classIndex: snapshot.data.snapshot.value
                                            .toList()[index],
                                      )));
                        },
                        child: Text(
                          "${snapshot.data.snapshot.value.toList()[index]["className"].toString().toUpperCase()} \n ${snapshot.data.snapshot.value.toList()[index]["classSection"].toString().toUpperCase()}",
                          style: TextStyle(fontSize: 20, shadows: [
                            Shadow(
                                // bottomLeft
                                offset: Offset(-1.5, -1.5),
                                color: Colors.black),
                            Shadow(
                                // bottomRight
                                offset: Offset(1.5, -1.5),
                                color: Colors.black),
                            Shadow(
                                // topRight
                                offset: Offset(1.5, 1.5),
                                color: Colors.black),
                            Shadow(
                                // topLeft
                                offset: Offset(-1.5, 1.5),
                                color: Colors.black),
                          ]),
                        ),
                      ),
                      padding: EdgeInsets.all(4.0),
                    );
                  } else {
                    return Visibility(
                      child: Text("Gone"),
                      visible: false,
                    );
                  }
                },
              );
            }
            return Center(
                child: Text(
              "No Class Registered",
              style: TextStyle(fontSize: 42),
            ));
          } else {
            return CircularProgressIndicator();
          }
        });   }

Answer 1

The way I solved having these empty spaces in a grid is to filter the list of widgets before using them in the grid:

List visibleWidgets = allWidgets.where((widget) => widget.show == true).toList();