iTextSharp.text.pdf.PdfLayerMembership.AddMember C# (CSharp) Метод

        public void AddMember(PdfLayer layer)
        {
            if (!layers.ContainsKey(layer)) {
                members.Add(layer.Ref);
                layers[layer] = null;
            }
        }

        // ===========================================================================
        public void Write(Stream stream)
        {
            // step 1
              using (Document document = new Document()) {
            // step 2
            PdfWriter writer = PdfWriter.GetInstance(document, stream);
            writer.PdfVersion = PdfWriter.VERSION_1_5;
            // step 3
            document.Open();
            // step 4
            PdfContentByte cb = writer.DirectContent;

            PdfLayer dog = new PdfLayer("layer 1", writer);
            PdfLayer tiger = new PdfLayer("layer 2", writer);
            PdfLayer lion = new PdfLayer("layer 3", writer);
            PdfLayerMembership cat = new PdfLayerMembership(writer);
            cat.AddMember(tiger);
            cat.AddMember(lion);
            PdfLayerMembership no_cat = new PdfLayerMembership(writer);
            no_cat.AddMember(tiger);
            no_cat.AddMember(lion);
            no_cat.VisibilityPolicy = PdfLayerMembership.ALLOFF;
            cb.BeginLayer(dog);
            ColumnText.ShowTextAligned(cb, Element.ALIGN_LEFT,
              new Phrase("dog"), 50, 775, 0
            );
            cb.EndLayer();
            cb.BeginLayer(tiger);
            ColumnText.ShowTextAligned(cb, Element.ALIGN_LEFT,
              new Phrase("tiger"), 50, 750, 0
            );
            cb.EndLayer();
            cb.BeginLayer(lion);
            ColumnText.ShowTextAligned(cb, Element.ALIGN_LEFT,
              new Phrase("lion"), 50, 725, 0
            );
            cb.EndLayer();
            cb.BeginLayer(cat);
            ColumnText.ShowTextAligned(cb, Element.ALIGN_LEFT,
              new Phrase("cat"), 50, 700, 0
            );
            cb.EndLayer();
            cb.BeginLayer(no_cat);
            ColumnText.ShowTextAligned(cb, Element.ALIGN_LEFT,
              new Phrase("no cat"), 50, 700, 0
            );
            cb.EndLayer();
              }
        }