//更新学生名字和引发分数变化事件
public void UpdateGrade(string nm, int grade)
{
GradeChangeEventArg arg = new GradeChangeEventArg(nm, grade);
this.OnGradeChange(arg);
}
public void Student_Grade(object sender, GradeChangeEventArg arg)
{
Student st = sender as Student;
Console.WriteLine($"{arg._name}班级{_classname}：同学{st._Name}收到期末成绩通知为{arg._Grade}");
}
protected void OnGradeChange(GradeChangeEventArg arg)
{
GradeChange?.Invoke(this, arg);
}