windows-phone-7 – 无尽的枢轴控制

当用户尝试返回前一天时,我的问题就出现了.在这种情况下,在Pivot项集合的开头添加一个新项.虽然添加有效,但显示的Pivot项始终是错误的(即新添加的项).在Pivot控件上设置SelectedItem没有帮助.

我认为Pivot可能不是我的任务的正确控制,所以任何关于使用什么视图或如何修复我的上述Pivot问题的帮助都非常感谢.

我的Viewmodel的代码,它实现了前进/后退一天.
Pages绑定到Pivot ItemSource.

public class TrackDayViewModel : HubViewModelBase
{
    private DateTime _CurrentDay;
    public DateTime CurrentDay
    {
        get { return _CurrentDay; }
        set
        {
            if (value.CompareTo (_CurrentDay) != 0)
            {
                _CurrentDay = value;
                OnPropertyChanged("CurrentDay");
            }
        }
    }

    public TrackDayViewModel ()
    {
        var day = DateTime.Now;

        CurrentDay = day.Midnight();

        Pages.Add(new DayViewModel(CurrentDay.AddDays(-1)));
        Pages.Add(new DayViewModel(CurrentDay));
        Pages.Add(new DayViewModel(CurrentDay.AddDays(1)));

        SelectedItem = Pages[1];

        this.PropertyChanged += (s,e) =>
        {
            if (e.PropertyName == "SelectedItem")
            {
                var si = SelectedItem as DayViewModel;

                if (si != null)
                {
                    var idx = Pages.IndexOf(SelectedItem);
                    if (idx==0)
                    {
                        Pages.Insert(0,new DayViewModel(si.Day.AddDays(-1)));
                        SelectedItem = Pages[1];
                    }
                    else if (idx == (Pages.Count - 1))
                    {
                        Pages.Add(new DayViewModel(si.Day.AddDays(1)));
                    }
                }
            }
        };
    }
}

编辑：改变解决了我的问题：

this.PropertyChanged += (s,e) =>
        {
            if (e.PropertyName == "SelectedItem")
            {
                var si = SelectedItem as DayViewModel;

                if (si != null)
                {
                    var idx = Pages.IndexOf(SelectedItem);

                    int nextIdx = (idx + 1) % 3;
                    int prevIdx = ((idx - 1)<0)  ? 2 : (idx-1);

                    Pages[nextIdx] = new DayViewModel(si.Day.AddDays(1));
                    Pages[prevIdx] = new DayViewModel(si.Day.AddDays(-1));
                }
            }
        };