CODEWITHSUNDEEP
c#wpfvalidationxamldatepicker
Gabriel Valente
Gabriel Valente

Reputation: 101

Disable datepicker textbox conversion/validation on focus lost

In the program I have one DatePicker that the user are allowed to not enter a date. But if the user enters one date and then he deletes it, the TextBox in the DatePicker does some kind of validation, and I want to disable that. Also, if I save the value after this "validation" the date entered before is the one saved.

Image from Gyazo

I have tried to set the date as null if it doesn't have any text, but that doesn't work.

private void PART_TextBoxFim_TextChanged(object sender, TextChangedEventArgs e)
{
    if (Dp_DataFim.Text == null)
    {
        Dp_DataFim.SelectedDate = null;
        Dp_DataFim.DisplayDate = DateTime.Today;
    }
}

Inside the class of the page I have this:

public Nullable<DateTime> Prop { get; set; }

The XAML of the datepicker is this one:

<DatePicker x:Name="Dp_DataFim" Grid.Row="0" Grid.Column="2" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="10,250,0,0" FontSize="16" Height="20" Width="230" SelectedDate="{Binding Prop}" IsTodayHighlighted="False" SelectedDateFormat="Short" BorderThickness="0" Padding="0" BorderBrush="{x:Null}" IsTabStop="True" SelectedDateChanged="Dp_DataFim_SelectedDateChanged" Visibility="Hidden">
    <DatePicker.Resources>
        <Style TargetType="{x:Type DatePickerTextBox}">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <TextBox x:Name="PART_TextBox" Text="{Binding Path=SelectedDate, RelativeSource={RelativeSource AncestorType={x:Type DatePicker}}, StringFormat='dd/MM/yyyy HH:mm:ss'}" Background="#FF494949" Foreground="#FFEEEEEE" BorderThickness="0" IsReadOnly="False" TextChanged="PART_TextBoxFim_TextChanged"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DatePicker.Resources>
</DatePicker>

I have noticed when this happens, I get a error like this one:

System.Windows.Data Error: 7 : ConvertBack cannot convert value '' (type 'String'). BindingExpression:Path=SelectedDate; DataItem='DatePicker' (Name='Dp_DataFim'); target element is 'TextBox' (Name='PART_TextBox'); target property is 'Text' (type 'String') FormatException:'System.FormatException: The string was not recognized as a valid DateTime value.
   em System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles)
   em System.Convert.ToDateTime(String value, IFormatProvider provider)
   em System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   em System.Windows.Data.BindingExpression.ConvertBackHelper(IValueConverter converter, Object value, Type sourceType, Object parameter, CultureInfo culture)'

Upvotes: 1

Views: 1395

Answers (1)

mm8
mm8

Reputation: 169180

Bind the SelectedDate property of the DatePicker to a Nullable<DateTime> source property.

If you change the format of the date by creating a custom ControlTemplate for the DatePickerTextBox where you bind its Text property to the SelectedDate property, you could then use a simple converter class to convert the empty string to a default(DateTime?):

public class StringToDateTimeConverter : IValueConverter
{
    private const string DateFormat = "dd/MM/yyyy HH:mm:ss";

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DateTime? dt = (DateTime?)value;
        return dt.HasValue ? dt.Value.ToString(DateFormat, CultureInfo.InvariantCulture) : string.Empty;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        string s = value.ToString();
        if (string.IsNullOrEmpty(s))
            return default(DateTime?);

        DateTime dt;
        return DateTime.TryParseExact(s, DateFormat, CultureInfo.InvariantCulture, DateTimeStyles.None, out dt) ? dt : default(DateTime?);
    }
}

Usage:

<DatePicker x:Name="Dp_DataFim" SelectedDate="{Binding MyProp}">
    <DatePicker.Resources>
        <local:StringToDateTimeConverter x:Key="StringToDateTimeConverter" />
        <Style TargetType="{x:Type DatePickerTextBox}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate>
                        <TextBox x:Name="PART_TextBox" Text="{Binding Path=SelectedDate, 
                                    RelativeSource={RelativeSource AncestorType={x:Type DatePicker}}, 
                                    Converter={StaticResource StringToDateTimeConverter}}" />
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </DatePicker.Resources>
</DatePicker>

Upvotes: 2

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