/// <summary>
/// 监听IAsyncDataContext的DataChanged事件。且保证其只发生一次。
/// </summary>
/// <param name="con"></param>
/// <param name="callBack">在异步加载数据完成后，调用callBack方法</param>
public static void ListenDataChangedOnce(this INotifyDataChanged con, Action callBack)
{
var dele = new DetachChangedEventDelegate();
dele._con = con;
dele._action = callBack;
dele._con.DataChanged += dele.OnDataChanged;
}
/// <summary>
/// 监听IAsyncDataContext的DataChanged事件。且保证其只发生一次。
/// </summary>
/// <param name="con"></param>
/// <param name="callBack">在异步加载数据完成后，调用callBack方法</param>
public static void ListenDataChangedOnce(this INotifyDataChanged con, Action callBack)
{
var dele = new DetachChangedEventDelegate();
dele._con = con;
dele._action = callBack;
dele._con.DataChanged += dele.OnDataChanged;
}