FormatString property for NumericUpDown

[LaurentInSeattle]

Where can I find any documentation about this FormatString property?

Apparently it does not work like a classic C# string used in string.Format...

Thanks

[LaurentInSeattle]

The FormatString needs to be as documented here:
https://learn.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings

If you try to use (like I did) a format string such as the ones in string.Format (...) with curly braces, this will fail.

[gehongyan]

If the value is not null or whitespace, but does not contain the character {, it will be wrapped into the format supported by string.Format.

Avalonia/src/Avalonia.Base/Data/Core/BindingExpression.cs

Lines 108 to 113 in b16975c

	_stringFormat = stringFormat switch
	{
	string s when string.IsNullOrWhiteSpace(s) => null,
	string s when !s.Contains('{') => $"{{0:{stringFormat}}}",
	_ => stringFormat,
	},

After that, the binding value will be formatted with string.Format if applicable.

Avalonia/src/Avalonia.Base/Data/Core/BindingExpression.cs

Lines 481 to 488 in b16975c

	if (StringFormat is { } stringFormat &&
	(TargetType == typeof(object) || TargetType == typeof(string)) &&
	!isTargetNullValue)
	{
	// The string format applies if we're targeting a type that can accept a string
	// and the value isn't the TargetNullValue.
	value = string.Format(ConverterCulture, stringFormat, value);
	}

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https://docs.avaloniaui.net/docs/basics/data/data-binding/data-binding-syntax#string-formatting