Get StringSize since iOS7

StringSize.cs

var dictionary = new NSDictionary(UIStringAttributeKey.Font, Font.Name); 
var attributes = new UIStringAttributes(dictionary); 
var size = text.GetSizeUsingAttributes(attributes); 

StringSizeWithBounds.cs

var bounds = new SizeF(width, height);
var text = new NSString(text ?? string.Empty);

var dictionary = new NSDictionary(UIStringAttributeKey.Font, font.Name);
var attributes = new UIStringAttributes(dictionary);

var options = NSStringDrawingOptions.UsesFontLeading | NSStringDrawingOptions.UsesLineFragmentOrigin;

var size = text.GetBoundingRect(bounds, options, attributes, null);