How to convert from Decimal to T?

Question

I've built a wrapper over NumbericUpDown control. The wrapper is generic and can support int? and double?

I would like to write a method that will do the following.

public partial class NullableNumericUpDown<T> : UserControl where T : struct
{
  private NumbericUpDown numericUpDown;


  private T? Getvalue()
  {
    T? value = numericUpDown.Value as T?; // <-- this is null :) thus my question
    return value;
  }}

of course there is no cast between decimal and double? or int? so I need to use a certain way of converting. I would like to avoid switch or if expressions.

What would you do?

To clarify my question I've provided more code...

Your question isn't quite clear enough. Is the GetValue method part of the wrapper? Or is numericUpDown an instance of the wrapper? Maybe a little more code showing what you are trying to achieve will help. — Paul Batum, Sep 21 '08 at 11:10
I asked a [related question](http://stackoverflow.com/questions/63694/creating-a-math-library-using-generics-in-c) last week. I think the answer could be effective in your case. — Sklivvz, Sep 21 '08 at 11:01
I failed to see how it can help. I would like to use a converter logic somehow. — ArielBH, Sep 21 '08 at 11:06
I think that the question is how to create this "something akin" — aku, Sep 22 '08 at 01:41

aku · Answer 1 · 2008-09-21T11:34:20.957

5

It's not clear how you gonna use it. If you want double create GetDouble() method, for integers - GetInteger()

EDIT:

Ok, now I think I understand your use case

Try this:

using System;
using System.ComponentModel;

static Nullable<T> ConvertFromString<T>(string value) where T:struct
{
    TypeConverter converter = TypeDescriptor.GetConverter(typeof(T));
    if (converter != null && !string.IsNullOrEmpty(value))
    {
        try
        {
            return (T)converter.ConvertFrom(value);
        }
        catch (Exception e) // Unfortunately Converter throws general Exception
        {
            return null;
        }
    }

    return null;
}

...

double? @double = ConvertFromString<double>("1.23");
Console.WriteLine(@double); // prints 1.23

int? @int = ConvertFromString<int>("100");
Console.WriteLine(@int); // prints 100

long? @long = ConvertFromString<int>("1.1");
Console.WriteLine(@long.HasValue); // prints False

edited Sep 21 '08 at 11:34

answered Sep 21 '08 at 11:03

aku

122,288
32
173
203

Why do you need genericы if all you need is double and int ? – aku Sep 21 '08 at 11:08
Aku, it's cool but unfortunately DoubleConveter does not support decimal :| – ArielBH Sep 21 '08 at 11:48
I don't understand what are you talking about. Why DoubleConverter? This code works decimal? @decimal = ConvertFromString("99999999999999999999999"); – aku Sep 21 '08 at 12:08
and this too: ConvertFromString("1.1") – aku Sep 21 '08 at 12:13

score 0 · Answer 2 · answered Sep 21 '08 at 11:16

0

Since this method will always return the result of

numericUpDown.Value

you have no cause for the value to be converted to anything other than Decimal. Are you trying to solve a problem you don't have?

answered Sep 21 '08 at 11:16

lotsoffreetime

1,100
5
11

Amy B · Answer 3 · 2008-09-22T14:10:20.510

public class FromDecimal<T> where T : struct, IConvertible
{
    public T GetFromDecimal(decimal Source)
    {
        T myValue = default(T);
        myValue = (T) Convert.ChangeType(Source, myValue.GetTypeCode());
        return myValue;
    }
}

public class FromDecimalTestClass
{
    public void TestMethod()
    {
        decimal a = 1.1m;
        var Inter = new FromDecimal<int>();
        int x = Inter.GetFromDecimal(a);
        int? y = Inter.GetFromDecimal(a);
        Console.WriteLine("{0} {1}", x, y);

        var Doubler = new FromDecimal<double>();
        double dx = Doubler.GetFromDecimal(a);
        double? dy = Doubler.GetFromDecimal(a);
        Console.WriteLine("{0} {1}", dx, dy);
    }
}

private T? Getvalue()
{
  T? value = null;
  if (this.HasValue)
    value = new FromDecimal<T>().GetFromDecimal(NumericUpDown);
  return value;
}

How to convert from Decimal to T?

3 Answers3