如何跳过项目构建器 gridview.builder Flutter Firebase Stream Builder 中的构建

我想删除 firebase 的某些内容，当 Streambuilder(gridview.builder) 到达它的索引（该索引将为空）时，它会忽略它，并且不要在该插槽中添加任何小部件并将其保留给其他人

这就是它的样子

我希望左侧和右侧的空白区域消失，并由其他小部件取代它

Firebase 数据库映像

 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();
          }
        });   }

我解决网格中存在这些空白空间的方法是在网格中使用它们之前过滤小部件列表：

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