CODEWITHSUNDEEP
c#.netvisual-studio-2010.net-4.0
now he who must not be named.
now he who must not be named.

Reputation: 9396

Passing interface members by value

    public void MethodSample1(Itest variable)
    {
        variable.TestString = "some sample data";
        Itest var1 = variable;
        Console.WriteLine(variable.TestString);
        MethodSample2(variable);
        Console.WriteLine(variable.TestString);
        Console.WriteLine(var1.TestString);

    }

    public void MethodSample2(Itest variable)
    {
        variable.TestString = "testdata";
    }

    public interface Itest
    {
      string TestString { get; set; }
    }

Expected both the console output lines print "some sample data" but it seems that TestString is being overwritten with the new value? is it not like "by default in C# all the values are passed by value?".

In short, how to preserve the value of "TestString" in MethodSample1?

(I ran into this problem because all my projects are based upon a single interface)

Even after preserving the value, it does reflect! strange!

Upvotes: 2

Views: 1032

Answers (3)

Botz3000
Botz3000

Reputation: 39650

The parameter is indeed passed by value, but the value you are passing is a reference to the original object.

If you want to preserve the original object's properties, you'll need to pass a copy of the original object. You could add a Clone() method to the interface or something similar:

public interface ITest
{
    string TestString { get; set; }
    ITest Clone();      
}

public class Test : ITest 
{
    string TestString { get; set; }
    ITest Clone() { 
        return new Test() { 
            TestString = this.TestString 
        }; 
    }
}

Or, you could rethink your current approach. Do you really need to change the property of the interface? Or could you use a variable of type string instead?

Upvotes: 2

Azodious
Azodious

Reputation: 13882

how to preserve the value of "TestString" in MethodSample1?

Store it in a local variable.

public void MethodSample1(Itest variable)
{
    variable.TestString = "some sample data";
    string localTestString = variable.TestString;

    Console.WriteLine(variable.TestString);

    MethodSample2(variable);
    variable.TestString = localTestString;

    Console.WriteLine(variable.TestString);

}

But, this is wrong way of doing things. If you tell a little more what do you want to achieve, we could help more.

Upvotes: 1

Habib
Habib

Reputation: 223392

For your current problem, I don't think you can prevent any method from modifying the parameter passed to it.

Your variable is a reference type object, In C# reference type's address is passed by value to a method, that is why you are seeing the change. For example if your method is written like:

public void MethodSample2(Itest variable)
{
    variable = null;
}

You won't see the change in your MethodSample1 method, since the reference address is passed by value.

is it not like "by default in C# all the values are passed by value?".

Value types are passed by value, in your case variable is a reference type.

You should see Parameter Passing C# by Jon Skeet

Not sure why you have to modify the passed object, For workaround you can create a temporary copy of the property and then set that value before existing from the method.

Upvotes: 5

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