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

Question

我想删除一些firebase，并且当Streambuilder（gridview.builder）到达它的索引为空时，它将忽略它，并且不在该插槽中添加任何小部件并将其保留给其他人使用

这看起来像

我希望左侧和右侧的空白区域消失，而其他小部件代替它

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();
          }
        });   }

Answer 1

我解决的在网格中保留这些空白的方法是在网格中使用小部件之前对其进行过滤：