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Return a general list

I am trying to return a general list after loading values ​​from a file. However, after repeatedly manipulating the type of manipulation, I still cannot agree with me. Code below; my questions:

  • Do I need to identify each type of key as I start below, or is there a faster way? I see that "where T: ..." may be appropriate here, but I would like to allow DateTime, int, string, double, etc., if possible, and I do not see how to do it with "where "
  • Why can't I add a DateTime element to a list that has a date and time?
  • When I try to get the type (listType), it seems like it is out of scope. Even when I declare a type in the line above where I use it, it says that such an object does not exist.

Thanks so much for your thoughts.

public static List<T> FileToGenericList<T>(string FilePath, int ignoreFirstXLines = 0, bool stripQuotes = true)
{
    List<T> output = new List<T>();

    Type listType = output.GetType().GetGenericArguments()[0];

    try
    {
        using (StreamReader stream = new StreamReader(File.Open(FilePath, FileMode.Open)))
        {
            string line;
            int currentLine = 0;

            while ((line = stream.ReadLine()) != null)
            {
                // Skip first x lines
                if (currentLine < ignoreFirstXLines) continue;

                // Remove quotes if needed
                if (stripQuotes == true)
                {
                    line = line.Replace(@"""", @"");
                }

                // Q1 - DO I HAVE TO HAVE THIS FOR EACH TYPE OR IS THERE A QUICKER WAY
                if (listType == typeof(System.DateTime))
                {
                    DateTime val = new System.DateTime();
                    val = DateTime.Parse(line);

                    // Q2 ERROR: 'Argument type is not assignable to parameter type 'T''                    
                    output.Add(val);

                    // For some reason the type 'listType' from above is now out of scope when I try a cast
                    output.Add((listType)val);
                }
                if (listType == typeof(System.String))
                {
                    //DateTime val = new System.DateTime();
                    //val = DateTime.Parse(line);
                    //output.Add(val.ToString());
                }

                // Continue tracking for line skipping purposes
                currentLine++;
            }
        }
    }
    catch (Exception ex)
    {
        throw new Exception("Error - there was a problem reading the file at " + FilePath + ".  Error details: " + ex.Message);
    }    
    return output;
}
+3
3

//Q1 -

, :

using System;
using System.Collections.Generic;

namespace AddGenericToList
{
    class Program
    {
        static void Main(string[] args)
        {
            var tc = new ListClass<string>();

            tc.Add("a value");
            tc.Add(123);
            tc.Add(DateTime.Now);
        }
    }

    internal class ListClass<T>
    {
        private readonly List<T> list = new List<T>();

        public void Add(object value)
        {
            list.Add((T)Convert.ChangeType(value, Nullable.GetUnderlyingType(typeof (T)) ?? typeof (T)));
        }
    }
}

. , DateTime string, int.

+2

, FileToGenericList, , , . , :

class Program
{
    static void Main(string[] args)
    {
        // second argument is a lambda that describes how to convert the line into the type you require
        var dateList = FileToGenericList<DateTime>("dates.txt", DateTime.Parse);
        var stringList = FileToGenericList<string>("strings.txt", s => s);
        var intList = FileToGenericList<int>("integers.txt", Int32.Parse); 

        Console.ReadLine();
    }

    static List<T> FileToGenericList<T>(string filePath, Func<string, T> parseFunc, int ignoreFirstXLines = 0, bool stripQuotes = true)
    {
        var output = new List<T>();

        try
        {
            using (StreamReader stream = new StreamReader(File.Open(filePath, FileMode.Open)))
            {
                string line;
                int currentLine = 0;

                while ((line = stream.ReadLine()) != null)
                {
                    // Skip first x lines
                    if (currentLine < ignoreFirstXLines)
                        continue;

                    // Remove quotes if needed
                    if (stripQuotes == true)
                        line = line.Replace(@"""", @"");

                    var parsedValue = parseFunc(line);
                    output.Add(parsedValue);
                    currentLine++;
                }
            }
        }
        catch (Exception ex)
        {
            throw new Exception("Error - there was a problem reading the file at " + FilePath + ".  Error details: " + ex.Message);
        }    
        return output;
   }
}
+3

№ 3: , " ", , . output.Add((listType)val); # - . , Type listType, - T, . @Pravin Pawar: output.Add(val as T); output.Add((T)val), T .

EDIT:

, (T)val , , T - DateTime, , . , :

 (T)Convert.ChangeType(val, typeof(T)));

Which converts your DateTime val to T (which is also a DateTime), which is enough to satisfy the compiler.

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