Setting StringFormat of WPF DatePicker inside UserControl

Question

I have a custom WPF UserControl that uses a DatePicker within it. I'm setting the display format of the DatePicker using the answer provided at this SO article

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

I would like to use a different format string for different instances of the control, so I'd like in some way to provide the format when I add the UserControl to the form, something like

<basecontrols:CustomControl 
    LabelWidth="{StaticResource LabelColumnWidth}" 
    Label="Custom Information" 
    DateDisplayFormat="dd-MMMM-yyyy" 
    />

Label and LabelWidth are Dependancy properties of the custom UserControl.

Is it possible to have bind the StringFormat to a control property, when it is inside a Binding ? If not, is there a way to do what I want to do?

Hope that makes sense

mm8 · Accepted Answer · 2019-11-04 15:38:45Z

1

Is it possible to have bind the StringFormat to a control property, when it is inside a Binding ?

No. You can't bind the StringFormat property of a Binding because it's not a dependency property.

What you could to is to define a DateDisplayFormat dependency property in your CustomControl (which I guess you have done already) and then override the OnApplyTemplate method and create the binding of the TextBox programmatically.

Alternatively, you could use a <MultiBinding> in the XAML markup that binds to both SelectedDate and DateDisplayFormat and use a multi converter that returns a string.

answered Nov 4, 2019 at 15:38

mm8

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2 Comments

Ian Boggs Over a year ago

I've tried to use MultiBinding, and it works when I set the value from code. However, when I change the value using the DatePicker, it reverts to a standard dd/MM/yy date format. I do have a DateDisplayFormat dep property so I'll try that next

mm8 Over a year ago

@IanBoggs: Your multi converter should be called whenever SelectedDate is set and you can then return whatever string you want.

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