Changing the string format of the WPF DatePicker

It appears, as per Wonko's answer, that you cannot specify the Date format in Xaml format or by inheriting from the DatePicker.

I have put the following code into my View's constructor which overrides the ShortDateFormat for the current thread:

CultureInfo ci = CultureInfo.CreateSpecificCulture(CultureInfo.CurrentCulture.Name);
ci.DateTimeFormat.ShortDatePattern = "dd-MM-yyyy";
Thread.CurrentThread.CurrentCulture = ci;

The accepted answer (thanks @petrycol) put me on the right track, but I was getting another textbox border and background color within the actual date picker. Fixed it using the following code.

        <Style TargetType="{x:Type Control}" x:Key="DatePickerTextBoxStyle">
            <Setter Property="BorderThickness" Value="0"/>
            <Setter Property="VerticalAlignment" Value="Center"/>
            <Setter Property="Background" Value="{x:Null}"/>
        </Style>

        <Style TargetType="{x:Type DatePickerTextBox}" >
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <TextBox x:Name="PART_TextBox"
                             Text="{Binding Path=SelectedDate, StringFormat='dd-MMM-yyyy', RelativeSource={RelativeSource AncestorType={x:Type DatePicker}}}" Style="{StaticResource DatePickerTextBoxStyle}" >
                        </TextBox>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

The WPF Toolkit DateTimePicker now has a Format property and a FormatString property. If you specify Custom as the format type, you can provide your own format string.

<wpftk:DateTimePicker
    Value="{Binding Path=StartTime, Mode=TwoWay}"
    Format="Custom"
    FormatString="MM/dd/yyyy hh:mmtt"/>

NOTE: This answer (originally written in 2010) is for earlier versions. See other answers for using a custom format with newer versions

Unfortunately, if you are talking about XAML, you are stuck with setting SelectedDateFormat to "Long" or "Short".

If you downloaded the source of the Toolkit along with the binaries, you can see how it is defined. Here are some of the highlights of that code:

DatePicker.cs

#region SelectedDateFormat

/// <summary>
/// Gets or sets the format that is used to display the selected date.
/// </summary>
public DatePickerFormat SelectedDateFormat
{
    get { return (DatePickerFormat)GetValue(SelectedDateFormatProperty); }
    set { SetValue(SelectedDateFormatProperty, value); }
}

/// <summary>
/// Identifies the SelectedDateFormat dependency property.
/// </summary>
public static readonly DependencyProperty SelectedDateFormatProperty =
    DependencyProperty.Register(
    "SelectedDateFormat",
    typeof(DatePickerFormat),
    typeof(DatePicker),
    new FrameworkPropertyMetadata(OnSelectedDateFormatChanged),
    IsValidSelectedDateFormat);

/// <summary>
/// SelectedDateFormatProperty property changed handler.
/// </summary>
/// <param name="d">DatePicker that changed its SelectedDateFormat.</param>
/// <param name="e">DependencyPropertyChangedEventArgs.</param>
private static void OnSelectedDateFormatChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    DatePicker dp = d as DatePicker;
    Debug.Assert(dp != null);

    if (dp._textBox != null)
    {
        // Update DatePickerTextBox.Text
        if (string.IsNullOrEmpty(dp._textBox.Text))
        {
            dp.SetWaterMarkText();
        }
        else
        {
            DateTime? date = dp.ParseText(dp._textBox.Text);

            if (date != null)
            {
                dp.SetTextInternal(dp.DateTimeToString((DateTime)date));
            }
        }
    }
}



#endregion SelectedDateFormat

private static bool IsValidSelectedDateFormat(object value)
{
    DatePickerFormat format = (DatePickerFormat)value;

    return format == DatePickerFormat.Long
        || format == DatePickerFormat.Short;
}

private string DateTimeToString(DateTime d)
{
    DateTimeFormatInfo dtfi = DateTimeHelper.GetCurrentDateFormat();

    switch (this.SelectedDateFormat)
    {
        case DatePickerFormat.Short:
            {
                return string.Format(CultureInfo.CurrentCulture, d.ToString(dtfi.ShortDatePattern, dtfi));
            }

        case DatePickerFormat.Long:
            {
                return string.Format(CultureInfo.CurrentCulture, d.ToString(dtfi.LongDatePattern, dtfi));
            }
    }      

    return null;
}

DatePickerFormat.cs

public enum DatePickerFormat
{
    /// <summary>
    /// Specifies that the date should be displayed 
    /// using unabbreviated days of the week and month names.
    /// </summary>
    Long = 0,

    /// <summary>
    /// Specifies that the date should be displayed 
    ///using abbreviated days of the week and month names.
    /// </summary>
    Short = 1
}

XAML

 <DatePicker x:Name="datePicker" />

C#

var date = Convert.ToDateTime(datePicker.Text).ToString("yyyy/MM/dd");

put what ever format you want in ToString("") for example ToString("dd MMM yyy") and output format will be 7 Jun 2017

I have solved this problem in an easy way ... Setting options Language in control.

Converter class:

public class DateFormat : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null) return null;
        return ((DateTime)value).ToString("dd-MMM-yyyy");
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

wpf tag

<DatePicker Grid.Column="3" SelectedDate="{Binding DateProperty, Converter={StaticResource DateFormat}}" Margin="5"/>

Hope it helps

Format exhibited depending on the location but this can be avoided by writing this:

  ValueStringFormat="{}{0:MM'-'yy}" />

And you will be happy!(dd'-'MM'-'yyy)

As Ben Pearce answered we can use the CultureInfo Class to take care of the Custom Format, I really think is the only logical way. And if you have different dateTimePickers which have different Format, you can use:

CultureInfo ci = CultureInfo.CreateSpecificCulture(CultureInfo.CurrentCulture.Name);
ci.DateTimeFormat.LongDatePattern = "MMM.yyyy"; //This can be used for one type of DatePicker
ci.DateTimeFormat.ShortDatePattern = "dd.MMM.yyyy"; //for the second type
Thread.CurrentThread.CurrentCulture = ci;

And then you can just change the DateFormat in the .xaml document.

  <DatePicker Name="dateTimePicker1" SelectedDateFormat="Long"  />