Question

Should I place every class in separate file? Even those short helper classes that are used only in one place? Like this one:

public class IntToVisibilityConverter : GenericValueConverter<int, Visibility>
{
    protected override Visibility Convert(int value)
    {
        return value == 0 ? Visibility.Collapsed : Visibility.Visible;
    }
}

Answer 1

That depends greatly of personal preference, but I like to do it.

In this case, I would have a folder inside my application called ValueConverters, and put all converters, including short ones, inside their own files.

I find it makes it easier to get an overview of what your project consist of from the Solution Explorer.