C# Can we pass Class type as parameter to Function and access class variables inside method

Question

Assume there's a base class

class base
{
  int x, y;
}

And 3 derived singleton classes A, B, C with x, y initialized to some value.

example :

class A : base { x = 1; y = 0;}
class B : base { x = 0; y = 1;}    
class C : base { x = 1; y = 1;}

Is there a way to Pass class as parameter to method and access that class's variable value. SO, One function that can update values for all 3 classes.

Intention :

int call (type classtype)
{
   int xvalue = classtype.x;
   int yvalue = classtype.y;
}

I've seen in some posts a mention of activator.CreateInstance(classtype) in How to pass a Class as parameter for a method? [duplicate]

But it doesn't answer how we can access variables of that class.

It should be `int call (base classtype)` and you would pass the instantiated object. — Legends, Oct 20 '17 at 20:55
The *type* doesn't have those variables. *Instances* of that type have those variables, so having the *type* doesn't give you any variables. — Servy, Oct 20 '17 at 20:55
Please show code for "classes A,B" - very unclear what you mean "class's variable value" as @Servy said. You may be referring to either static class fields/propertied *or* instance fields/properties - would be clear if code actually C# and not some pseudo-language. — Alexei Levenkov, Oct 21 '17 at 00:12
@AlexeiLevenkov : well I know type doesnt give any variables. That's why I explained it as what are intentions to get in return. Also, A, B & C are nothing but extending same vars and initializing to let's A(1,0) B(0,1) & C(1,1). Now I am expecting update these initialized values runtime. I dont want to implement 3 functions for 3 classes so would like to know if we can simply to one generic for all 3. — akshay dhule, Oct 24 '17 at 23:49

score 1 · Answer 1 · answered Oct 20 '17 at 20:56

1

Your method needs to accept the Type and then you can access static properties because you don't have the instance.

int Call(Type classType)
{
   var xvalue = (int)classType.GetProperty("x", BindingFlags.Public | BindingFlags.Static).GetValue(null, null);
   var yvalue = (int)classType.GetProperty("y", BindingFlags.Public | BindingFlags.Static).GetValue(null, null);
}

Although I have a feeling what you're really looking for is just simple inheritance or an interface as your parameter.

answered Oct 20 '17 at 20:56

Yuriy Faktorovich

67,283
14
105
142

And how do you call this method? – Steve Oct 20 '17 at 21:02
@Steve `Call(typeof(MyType))` – Alexei Levenkov Oct 20 '17 at 21:03
And this result (to me) in a null returned by GetProperty with the NRE just following behind – Steve Oct 20 '17 at 21:06
Hello Yuriy, looks like it's too much efforts to get value of one variable. In my case where there're 40-50 vars. It also needs capability of assigning values to that class var. I forgot to mention A, B, C are singleton classes. – akshay dhule Oct 20 '17 at 21:34
This is just going to throw an exception at runtime as there are no such static fields on the type. – Servy Oct 20 '17 at 21:39
@akshaydhule If they're singletons, then why not use a Factory Design Pattern, pass in the Factory and let it give you back the correct instances of the classes to use? – Yuriy Faktorovich Oct 20 '17 at 21:40
@akshaydhule also, why do your types have that many properties, seems excessive in most scenarios. – Yuriy Faktorovich Oct 20 '17 at 21:41

mattshu · Answer 2 · 2017-10-21T01:10:24.520

1

You could change Call to accept the base class that A,B,C derives from:

int Call(base theClass)
{
    if (theClass is A)
    {
        var ax = theClass.x;
        var ay = theClass.y;
    }
    else if (theClass is B)
    {
        // etc       
    }
    // etc
}

edited Oct 21 '17 at 01:10

answered Oct 20 '17 at 21:17

mattshu

96
11

2

Usually when you find your self doing this it is a sign of code smell. Instead of having a bunch of `is` checks you just make two overloads `Call(A theClass)` and `Call(B theClass)` – Scott Chamberlain Oct 20 '17 at 21:22
1

The thing is functionality is same for A, B and C and it's not efficient to set different functions/process for each class, Instead we should be able to send a para and depending on that create/access instance of respective class. – akshay dhule Oct 20 '17 at 22:43

C# Can we pass Class type as parameter to Function and access class variables inside method

2 Answers2