C# Parse string to type known at runtime

Question

I have a file holding some of the variables of a class, and each line is a pair : variable, value. I'm looking for a way to load these at runtime (a-la XmlSerializer), using reflection.

Is there a way to parse a string into a Type known only at runtime?

The following is a wishful code sample where the last line (with the pi.SetValue() is not correct, because PropertyType is of class Type which does not have a generic Parse() method.

using (var sr = new StreamReader(settingsFileName))
{
    String  line;
    while ((line = sr.ReadLine()) != null)
    {
        String[] configValueStrs = line.Trim().Split(seps);

        PropertyInfo pi = configurableProperties
                .Single(p => p.Name == configValueStrs[0].Trim());

        //How do I manage this?
        pi.SetValue(this, pi.PropertyType.Parse(configValueStrs[1].Trim()), null);
     }
 }

Since all of the relevant variables are Ints, Doubles, Strings or Booleans, as a last resort, I can Switch on the type and use the corresponding ToType() method, but I bet there is a more elegant solution.

Solution 1

You can use the static Convert.ChangeType method for that. It takes an object as its first parameter and a Type instance you want to convert the object to. The return value is of the type you requested or null if no suitable conversion was found. This method throw 4 different exceptions, from which three are caused by the value it tries to convert. You might want to catch and handle these.

Use the function as follows in your example:

// Convert.ChangeType can throw if the string doesn't convert to any known type
    pi.SetValue(this
      , Convert.ChangeType(configValueStrs[1], pi.PropertyType) 
      , null); 

Solution 2

TypeConverters are the way to go. Take a look here for a good example of what to do.

Nicked straight from hanselmans blog:

public static T GetTfromString<T>(string mystring)
{
   var foo = TypeDescriptor.GetConverter(typeof(T));
   return (T)(foo.ConvertFromInvariantString(mystring));
}

Solution 3

I believe that TypeConverters, Specifically StringConverter can help you with this problem.

http://msdn.microsoft.com/en-us/library/system.componentmodel.stringconverter.aspx

Comments

[Arical]

+1 to this as it will handle GUIDS, Convert.ChangeType will not

[Peter]

Check this: chrismarinos.com/default-typeconverters-and-objects Also in my own experience, the default implementation can't do anything.

[Peter]

Thanks, helped me out of a sticky situation!

[cdiggins]

Good answer, but that code is rather inelegant, and in some cases you have the type at run-time, not compile-time. See: stackoverflow.com/a/70354581/184528