Question

Paragraph p = new Paragraph();

void Function(var inline)
{
    var r = (inline);
    string rSer = XamlWriter.Save(r);
    var inl1 = XamlReader.Parse(rSer);
    p.Inlines.Add(inl1); // error The best overloaded method match for System.Windows.Documents.InlineCollection.Add(System.Windows.UIElement)' has some invalid arguments    
}

inline type can be System.Windows.Documents.Run or System.Windows.Documents.Span.

How do I know the type of inline and lead to it?

I need something like this:

Type t = Type.GetType(inline.GetType().ToString()); // results in t == null 
p.Inlines.Add(inline as t);

Answer 1

Since System.Windows.Documents.Run and System.Windows.Documents.Span both derive from System.Windows.Documents.Inline it could be as simple as:

// untested
void Function(Inline inline1)
{
    string rSer = XamlWriter.Save(inline1);
    var inline2 = XamlReader.Parse(rSer) as Inline;
    p.Inlines.Add(inline2); 
}