Question

noob to C# here, using iTextSharp examples from around SO I’ve made a basic exe to change title, description and keywords to an existing PDF. Using MS Visual C# 2010, I don’t understand all this ‘Generic’ change to C#, so I’m getting this error:

Cannot implicitly convert type 'System.Collections.Generic.Dictionary<string,string>' to 'System.Collections.Hashtable'

and

Cannot implicitly convert type 'System.Collections.Hashtable' to 'System.Collections.Generic.IDictionary<string,string>'. An explicit conversion exists (are you missing a cast?)

The Code:

using System;
using System.Collections;
using System.IO;
using System.Linq;
using System.Text;
using iTextSharp.text.pdf;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            if ((args == null) || (args.Length < 3))
            {
                Console.WriteLine("args: PDFProp [fileName] [outputPath] [Title] [Description] [Keywords]");
                Console.WriteLine();
                Console.Write("<Continue>");
                Console.ReadLine();
                return;
            }

            string filePath = args[0];
            string newFilePath = args[1];
            string title = args[2];
            string desc = "";
            string keywords = "";
            if (args.Length > 3)
                desc = args[3];
            if (args.Length > 4)
                keywords = args[4];

            Console.Write(filePath + "->" + newFilePath + " title: " + title + " description: " + desc + " keywords: " + keywords);
            Console.WriteLine();
            Console.ReadLine();

            PdfReader pdfReader = new PdfReader(filePath);
            using (FileStream fileStream = new FileStream(newFilePath, FileMode.Create, FileAccess.Write))
            {
                //   string title = pdfReader.Info["Title"] as string;           

                PdfStamper pdfStamper = new PdfStamper(pdfReader, fileStream);

                // The info property returns a copy of the internal HashTable
                Hashtable newInfo = pdfReader.Info;             // error 1 

                newInfo["Title"] = title;

                if (args.Length > 3)
                    newInfo["Description"] = desc;
                if (args.Length > 4)
                    newInfo["Keywords"] = keywords;

                pdfStamper.MoreInfo = newInfo;                  // error 2

                pdfReader.Close();
                pdfStamper.Close();
            }
        }
    }
}

Answer 1

Change the below line:

Dictionary<string,string> newInfo = pdfReader.Info;             

instead of

Hashtable newInfo = pdfReader.Info;

Should fix both errors.

The reason why this is happening is because you are trying to cast from a Hashtable to a Generic Dictionary and the hashtable does not have an implicit type conversion available for this. look here to see the difference between a hashtable and a Dictionary.