How to change DatePicker width?

[maguro1kan]

How can I properly change the width of a DatePicker?

<DatePicker SelectedDate="{Binding SelectedDate}"
            Width="250"
            IsVisible="{Binding IsCustomDateVisible}"
            Margin="0 10 0 0" />

And I want to make the width of the month in the DatePicker smaller.

[timunie]

looks like you need to change the entire control template here, as ColumnDefs are hard-coded:

Avalonia/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml

Line 99 in 7a7ab8e

<Grid Name="PART_ButtonContentGrid" ColumnDefinitions="78*,Auto,132*,Auto,78*">

MinWidth and MaxWidth can be overridden here:

Avalonia/src/Avalonia.Themes.Fluent/Controls/DatePicker.xaml

Lines 34 to 35 in 7a7ab8e

	<x:Double x:Key="DatePickerThemeMinWidth">296</x:Double>
	<x:Double x:Key="DatePickerThemeMaxWidth">456</x:Double>

[timunie]

copy & paste the two lines into App.Resources. Change the values, done.

[maguro1kan]

Thank you. I understand now.
Could you please explain how to modify this part?
<Grid Name="PART_ButtonContentGrid" ColumnDefinitions="78*,Auto,132*,Auto,78*">

[timunie]

Copy & paste entire ControlTemplate to your own Style. No other option I'm afraid.

[robloo]

I recently looks into doing exactly this with the FluentAvalonia theme. Like typical WinUI-code it isn't designed to be resizable in all cases. This control is especially tricky because you want the flyout to open with the same width as the control. Therefore, the control width depends on the flyout width requirements.

I would highly suggest switching to a CalendarDatePicker in situations where width is constrained. Although that has slower selection in some cases until/if #5656 is implemented.

[PinkSerenity]

Copy & paste entire ControlTemplate to your own Style. No other option I'm afraid.

I'm sorry, I still don't really know how to do it. I copy-pasted the ControlTheme that contains that line, but nothing changes if I modify the coloumn definitions. I know that the theme works because I can easily change the background of the month to red, but changing the column definitions does nothing. Could you please help me?