我做了我认为是正确的更改，然而，现在我收到一个错误，说我不能在这里使用for Each，因为它可能返回空.我不能用‘！’来强迫它.因为然后我得到了另一个错误，关于不能这样做，因为方法‘forEach’没有为类型‘Object’定义.
void loadStudentList(){
// function that loads all students from firebase database and display them in list view
FirebaseDatabase.instance.ref("students").once()
.then((databaseEvent) {
print("Successfully loaded the data");
print(databaseEvent);
print("Key:");
print(databaseEvent.snapshot.key);
print("value:");
print(databaseEvent.snapshot.value);
print("Iterating the value map");
var studentTmpList = [];
databaseEvent.snapshot.value!.forEach((k, v) {
print(k);
print(v);
studentTmpList.add(v);
});
print("Final student list");
print(studentTmpList);
studentList = studentTmpList;
setState(() {
});
}).catchError((error) {
print("Failed to load the data");
print(error);
});
}