DateTimePicker日历默认为上个月/年份

Question

When the DateTime? source of my DateTimePicker control is changed to null and I want to select another date, the calendar drop down defaults to the last month and year selected.

I am using the DateTimePicker for DOB so the months and years will vary greatly and I would rather the calendar reset to the current month and year when the data source is changed to null. The DateTimePicker from the WPFToolkit does this but I don't want the spinner or the time selection it comes with and cannot find the means to hide those.

I am using the MVVM design pattern and want to avoid immediate code-behind.

XAML from view:

<DatePicker Height="25" HorizontalAlignment="Left" Margin="53,47,0,0" 
    Name="dpEventDate" VerticalAlignment="Top" Width="115" 
    SelectedDate="{Binding EventItem.BirthDate, Mode=TwoWay, 
    UpdateSourceTrigger=PropertyChanged}" />

C# from view model: (Event is a class I made in the model)

private Event _eventItem;

public event PropertyChangedEventHandler PropertyChanged;
public RelayCommand CreateCommand { get; private set; }

public Event EventItem
{
    get { return _eventItem; }
    set { _eventItem = value; OnPropertyChanged("EventItem"); }
}

public MainViewModel()
{
    EventItem = new Event();
    CreateCommand = new RelayCommand(CreateEvent);
}

protected void OnPropertyChanged(string name)
{
    PropertyChangedEventHandler handler = PropertyChanged;

    if (handler != null)
    {
        handler(this, new PropertyChangedEventArgs(name));
    }
}

If there is anymore detail I can provide to help you help me, just let me know.

Answer 1

Per Adam's suggestion, here is the code in the view model that has helped me reset the DateTimePicker's Calendar display:

private Event _eventItem;
private DateTime? _viewDate;

public event PropertyChangedEventHandler PropertyChanged;
public RelayCommand CreateCommand { get; private set; }

public Event EventItem
{
    get { return _eventItem; }
    set { _eventItem = value; OnPropertyChanged("EventItem"); }
}

// Decoy DateTime property
public DateTime? ViewDate
{
    get { return _viewDate; }
    set
    { 
        _viewDate = value;
        EventItem.EventDate = _viewDate; // Update the source

        OnPropertyChanged("ViewDate");
    }
}

public MainViewModel()
{
    EventItem = new Event();
    CreateCommand = new RelayCommand(CreateEvent);
}

private void CreateEvent()
{
    ViewDate = DateTime.Today; // Important for resetting the calendar display
    // Save input and set EventItem to new event for a clean slate
}

protected void OnPropertyChanged(string name)
{
    PropertyChangedEventHandler handler = PropertyChanged;

    if (handler != null)
    {
        handler(this, new PropertyChangedEventArgs(name));
    }

    // Important if you want your DatePicker control to be empty
    if(name.Equals("ViewDate") && DateTime.Today.Equals(ViewDate))
    {
        ViewDate = null;
    }
}