String Format Not Being Applied

Question

<TextBox
    Background="#FAFAD2"
    Focusable="False"
    HorizontalContentAlignment="Center"
    Style="{StaticResource TextBoxKey}"
    Text="{Binding Path=LastUpdate, Converter={StaticResource conDate}, StringFormat='MMMM d, yyyy'}" />

Here are the relevant parts of the converter:

Private LowerLimit As New Date(2019, 12, 31)

Public Function Convert(value As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IValueConverter.Convert
	If IsDate(value) Then
		Dim val As Date = CDate(value)
		Return If(val > LowerLimit, CStr(val), String.Empty)
	Else
		Return String.Empty
	End If
End Function

And yet the displayed date is, for example, 9/1/2020

Why is the date not being displayed properly?

Answer 1

Try this converter:

Public Function Convert(value As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IValueConverter.Convert
    If IsDate(value) Then
        Dim val As Date? = CDate(value)
        Return If(val > LowerLimit, val, Nothing)
    Else
        Return Nothing
    End If
End Function

StringFormat does not work if the value is a string, not date.

Alternatively, you can format the date (using val.ToString("MMMM d, yyyy")) inside the converter and return the formatted string.