How to clear Calendar Date Picker Selected Values in UWP, C#

Question

I have a data-grid control and a series of controls that filter data in that data grid.

Those controls can be grouped into two as follows.

• Filter Combo Box (which contains Today , Yesterday , Last Week , Last Month )
• Two Calendar Date Picker and a button (which are From and To , when I clicked the button, the event takes values of those From and To date values and do the work)

Now, I want to do some UX works as follows.

• When the selected item of Filter Combo Box is changed, the values of two calendar date picker are cleared.
• When the button is clicked, the selected item of Filter Combo Box is cleared and set back to its original placeholder text.

I can manage it works for requirement 2 but 1 is not going well. Below is my event handlers. I'm not using MVVM. Just with code-behind.

private void SelectionChanged_Filter(object sender, SelectionChangedEventArgs e)
{
    /*DatePicker_FromDate.ClearValue(CalendarDatePicker.DateProperty);
      DatePicker_FromDate.PlaceholderText = "Pick a Date";
      DatePicker_ToDate.ClearValue(CalendarDatePicker.DateProperty);
      DatePicker_ToDate.PlaceholderText = "Pick a Date";*/

      DatePicker_FromDate.Date = null
      DatePicker_ToDate.Date = null;
}

 private void ButtonClick_Filter(object sender, Windows.UI.Xaml.RoutedEventArgs e)
 {
      // Clear the Filter Combobox's selected value
      ComboBox_Filter.SelectedIndex = -1;

      // EXCEPTION is in the below line:
      var fromDate = Convert.ToDateTime(DatePicker_FromDate.Date.ToString()).ToString("dd-MM-yyyy");
      var toDate = Convert.ToDateTime(DatePicker_ToDate.Date.ToString()).ToString("dd-MM-yyyy");

      //...
}

The EXCEPTION is:

System.FormatException: 'String '' was not recognized as a valid DateTime.'

I think setting null to date value of the calendar date picker is invalid. How can I clear those values when I changed the combobox?

Answer 1

Update: For clearing the value of CalendarDatePicker, you could set Date property to null like following.

DatePicker_FromDate.Date = null;
DatePicker_ToDate.Date= null;

For pass the value,first you could judge whether it is null then operate its value.

string toDate= = DatePicker_ToDate.Date == null ? "" : DatePicker_ToDate.Date.Value.ToString("dd/MM/yyyy");

Answer 2

If you are setting the Date property to null , the string will be null as well: using the following code that uses the safe-navigation operator ( ?. ):

var fromDate = DatePicker_FromDate.Date?.ToString("dd-MM-yyyy");
var toDate = DatePicker_ToDate.Date?.ToString("dd-MM-yyyy");

I guess this is what you want.

Also note that it's pointless to first convert a DateTime to a string just to convert it back to a DateTime and then convert it to a string again...