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How to Resolve Warning "CS0109: The member 'member' does not hide an accessible member" in C#

The Compiler Warning CS0109 is a code cleanup warning. The message reads: "The member 'Child.Method' does not hide an accessible member. The new keyword is not required."

In C#, the new modifier is used explicitly to hide a member inherited from a base class (shadowing). This warning occurs when you apply the new keyword to a method, property, or field, but the compiler cannot find any member in the base class with the same name to hide. Essentially, the compiler is saying: "You are trying to solve a naming conflict that doesn't exist."

This guide explains why this redundancy happens and how to keep your code clean.

Understanding the 'new' Modifier​

The new keyword is designed for this specific scenario:

  • Parent has public void DoWork().
  • Child wants its own public void DoWork(), unrelated to the parent's version.
  • You add new to the Child's method to suppress the collision warning (CS0108).

If the Parent does not have DoWork(), adding new to the Child serves no purpose.

Scenario 1: Refactoring Leftovers (The Most Common Cause)​

This usually happens after code refactoring. Perhaps the base class used to have a method with that name, but it was deleted or renamed. The derived class still has the new keyword, which is now obsolete.

Example of error​

public class BaseClass
{
    // Formerly: public void Compute() { ... }
    // This method was removed or renamed, so the base is now empty.
}

public class DerivedClass : BaseClass
{
    // ⛔️ Warning CS0109: The member 'Compute' does not hide an accessible member. 
    // The new keyword is not required.
    public new void Compute()
    {
        System.Console.WriteLine("Computing...");
    }
}

Solution: Remove the Keyword​

Simply delete the new modifier. It changes nothing about how the code executes.

public class DerivedClass : BaseClass
{
    // ✅ Correct: No base member to hide, so just declare it normally.
    public void Compute()
    {
        System.Console.WriteLine("Computing...");
    }
}

Scenario 2: Hiding Private Members​

Member hiding only applies to accessible members (public, protected, or internal). If the base class has a private method, that method is invisible to the child class. Since the child class cannot see it, it cannot "hide" it.

Example of error​

public class Parent
{
    // Private members are not inherited in a visible way.
    private void Secret() { }
}

public class Child : Parent
{
    // ⛔️ Warning CS0109: You cannot hide something you cannot see.
    // To the compiler, 'Secret' in Child is a brand new method 
    // that has no relation to 'Secret' in Parent.
    public new void Secret() { }
}

Solution​

Remove the new keyword. The two methods are already distinct because the parent's version is strictly private.

public class Child : Parent
{
    // ✅ Correct: This is implicitly a new method.
    public void Secret() { }
}
note

If you change the Parent method from private to protected or public later, the new keyword (or renaming) would then become necessary to avoid a collision.

Conclusion​

CS0109 is a housekeeping message.

  1. Check the Base Class: Does the member you are trying to hide actually exist in the parent?
  2. Check Accessibility: Is the parent member private? If so, you don't need new.
  3. The Fix: Simply delete the new keyword. Your code will behave exactly the same, but the warning will disappear.

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