/// <summary>
/// 添加子项
/// </summary>
/// <param name="task">子项</param>
/// <returns>添加的子项</returns>
public Task AddChild(Task task)
{
if (task == null || task.IsTransient())
{
throw new ArgumentException("任务子项参数为空！");
}
Children.Add(task);
task.SetParent(this);
return task;
}
