C# : using a variable when being passed it's string name

Question

so if the string name of a variable is passed into a method, I know which variable to use.

in the following example, the area I need help with is PrintVar(string)...turning the string argument into the variable...so that it prints out "here be variable 1" and "here be variable 2" respectively...Thanks!

class ReflectionTest
{    
    class MyObj
    {
        private string myvar;

        public MyObj(string input)
        {   this.myvar = input; }

        public override string ToString()
        {   return ("here be " + myvar);    }   
    }

    class MyClass
    {
        private MyObj var1;
        private MyObj var2;

        public MyClass()
        {   
            var1 = new MyObj("variable 1");
            var2 = new MyObj("variable 2");
        }

        public void PrintVar(string theVariable)
        { 
            Console.WriteLine(theVariable); 
        }   
    }


    static void Main()
    {
        MyClass test = new MyClass();
        test.PrintVar("var1");
        test.PrintVar("var2");
    }
}

Most times, it's much easier and better to use collections.

Chibueze Opata
– Chibueze Opata

2012-03-09 07:06:24 +00:00
Commented Mar 9, 2012 at 7:06 — Chibueze Opata
– Chibueze Opata, Commented Mar 9, 2012 at 7:06

Marc Gravell · Accepted Answer · 2012-03-09 07:01:13Z

6

If you need to fetch things by name, then personally I'd start by using a dictionary in the internal implementation, i.e.

private readonly Dictionary<string,MyObj> fields =new Dictionary<string,MyObj>();

public MyClass()
{
    fields["var1"] = new MyObj("variable 1");
    fields["var2"] = new MyObj("variable 2");
}
public void PrintVar(string fieldName)
{
    Console.WriteLine(fields[fieldName]);
}

The other option would be reflection (GetType().GetFields()):

public void PrintVar(string fieldName)
{
    Console.WriteLine(GetType().GetField(fieldName,
        BindingFlags.NonPublic | BindingFlags.Instance).GetValue(this));
}

answered Mar 9, 2012 at 7:01

Marc Gravell

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4 Comments

user1229895 Over a year ago

Thank you! I appreciate the reflection example and your recommended Dictionary implementation ;-)

user1229895 Over a year ago

one additional Question... if I added...public void WriteOut(){ Console.WriteLine("thank you"); }...to the 'MyObj' class...how would I call that within PrintVar(string)? i guess I'm still not sure what reflection returns...

Marc Gravell Over a year ago

@user1229895 either fields[fieldName].WriteOut(); or ((MyObj)GetType().GetField({same as before}).GetValue(this)).WriteOut();

user1229895 Over a year ago

very much obliged again! you are a sage ;-)

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