我在编写代码时遇到过几次这个问题，我想我只是不理解SwiftUI执行代码顺序的方式。
我在上下文模型中有一个方法，它从Firebase中获取数据，我在.onAppear中调用了这个方法，但是在运行了整个for循环之后，这个方法并没有执行方法中的最后一行。
当我在不同的位置设置断点时，代码似乎首先只是运行，而没有进行for循环，然后它再次返回到方法，然后运行一次for循环，然后它跳到其他一些奇怪的位置，然后再次返回到方法...
我想我就是不明白？
与主/后台线程有关吗？您能帮助我吗？
这是我的代码。
调用方法getTeachersAndCoursesInSchool的UI视图的一部分

VStack {
  //Title
  Text("Settings")
    .font(.title)

  Spacer()

  NavigationView {
    VStack {
      NavigationLink {
        ManageCourses()
          .onAppear {
            model.getTeachersAndCoursesInSchool()
          }
      } label: {
        ZStack {
          // ...
        }
      }
    }
  }
}

下面是我的方法的for循环：

//Get a reference to the teacher list of the school
let teachersInSchool = schoolColl.document("TeacherList")

//Get teacherlist document data
teachersInSchool.getDocument { docSnapshot, docError in
  if docError == nil && docSnapshot != nil {

    //Create temporary modelArr to append teachermodel to
    var tempTeacherAndCoursesInSchoolArr = [TeacherModel]()

    //Loop through all FB teachers collections in local array and get their teacherData
    for name in teachersInSchoolArr {

      //Get reference to each teachers data document and get the document data
      schoolColl.document("Teachers").collection(name).document("Teacher data").getDocument {
        teacherDataSnapshot, teacherDataError in

        //check for error in getting snapshot
        if teacherDataError == nil {

          //Load teacher data from FB
          //check for snapshot is not nil
          if let teacherDataSnapshot = teacherDataSnapshot {

            do {
              //Set local variable to teacher data
              let teacherData: TeacherModel = try teacherDataSnapshot.data(as: TeacherModel.self)

              //Append teacher to total contentmodel array of teacherdata
              tempTeacherAndCoursesInSchoolArr.append(teacherData)
            } catch {
              //Handle error
            }
          }

        } else {
          //TODO: Error in loading data, handle error
        }
      }
    }
    //Assign all teacher and their courses to contentmodel data
    self.teacherAndCoursesInSchool = tempTeacherAndCoursesInSchoolArr

  } else {
    //TODO: handle error in fetching teacher Data
  }
}

这个方法正确地将数据赋给了tempTeacherAndCoursesInSchoolArr，但是在最后一行，这个方法没有将tempTeacherAndCoursesInSchoolArr赋给self.teacherAndCoursesInSchool，为什么它不这样做呢？