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How to Resolve Error "CS0534: 'class' does not implement inherited abstract member 'member'" in C#

The Compiler Error CS0534 is an inheritance compliance error. The message reads: "'DerivedClass' does not implement inherited abstract member 'BaseClass.Member'".

In C#, an abstract class defines a contract. It declares methods or properties that have no code body (implementation). When a non-abstract (concrete) class inherits from that abstract class, it signs a contract promising to provide the missing code for every single abstract member. If you forget even one, or if you fail to mark the implementation with override, the compiler raises CS0534.

This guide explains how to fulfill these inheritance contracts.

Understanding the Abstract Contract​

  • Abstract Method: public abstract void DoWork(); (A "To-Do" item).
  • Concrete Class: Must check off every "To-Do" item by implementing them.

If your class is not marked abstract, it must be complete. It cannot have any "holes" in its logic inherited from a parent.

Scenario 1: Missing Implementation​

This is the standard cause. You inherit from a base class but haven't written the code for its abstract methods yet.

Example of error​

public abstract class DatabaseConnection
{
    public abstract void Open();
    public abstract void Close();
}

// ⛔️ Error CS0534: 'SqlServerConnection' does not implement 
// inherited abstract member 'DatabaseConnection.Open()' 
// (and likely .Close() as well).
public class SqlServerConnection : DatabaseConnection
{
    // The class body is empty. The contract is unfulfilled.
}

Solution: Override the Members​

You must implement every abstract member using the override keyword.

public class SqlServerConnection : DatabaseConnection
{
    // ✅ Correct: Implementing Open
    public override void Open()
    {
        Console.WriteLine("SQL Connection Opened");
    }

    // ✅ Correct: Implementing Close
    public override void Close()
    {
        Console.WriteLine("SQL Connection Closed");
    }
}
tip

Visual Studio Shortcut: Place your cursor on the class name (SqlServerConnection), press Ctrl + . (or click the lightbulb), and select "Implement abstract class". The IDE will generate the method stubs for you automatically.

Scenario 2: Signature Mismatch (Typos)​

Sometimes you think you implemented the method, but you made a small mistake in the name, parameter types, or return type. Because the signature doesn't match exactly, the compiler thinks you created a new, unrelated method, leaving the abstract one unimplemented.

Example of error​

public abstract class Shape
{
    public abstract double CalculateArea();
}

public class Circle : Shape
{
    public double Radius { get; set; }

    // ⛔️ Error CS0534: 'Circle' does not implement 'Shape.CalculateArea'.
    // Why? Because we typed 'Calculatearea' (lowercase 'a').
    // Without the 'override' keyword, this is just a new method.
    public double Calculatearea() 
    {
        return Math.PI * Radius * Radius;
    }
}

Solution: Fix Spelling and Add 'override'​

Ensure the signature matches exactly and always use override. If you use override and the name is wrong, the compiler gives a clearer error (CS0115 "no suitable method to override") instead of the vague CS0534.

public class Circle : Shape
{
    public double Radius { get; set; }

    // ✅ Correct: Exact spelling and explicit override.
    public override double CalculateArea()
    {
        return Math.PI * Radius * Radius;
    }
}

Scenario 3: Intermediate Inheritance (Passing the Buck)​

Sometimes you are building a class hierarchy (e.g., Grandparent -> Parent -> Child). If Parent inherits from Grandparent but is not ready to implement the abstract methods yet, Parent itself must be marked abstract.

Example of error​

Vehicle defines Move. Car inherits Vehicle but doesn't implement Move. Car is not abstract.

public abstract class Vehicle
{
    public abstract void Move();
}

// ⛔️ Error CS0534: 'Car' does not implement 'Vehicle.Move'.
// Since 'Car' is not abstract, it MUST implement everything.
public class Car : Vehicle
{
    // No implementation here
}

Solution: Mark as Abstract​

If Car is meant to be a base class for Sedan and Truck, mark Car as abstract. This passes the responsibility of implementing Move down to the next generation.

// ✅ Correct: 'Car' is now abstract. It doesn't need to implement Move.
public abstract class Car : Vehicle
{
    public int Wheels { get; set; }
}

// Now the concrete child must do it
public class Sedan : Car
{
    // ✅ Correct: Implementation provided finally.
    public override void Move() 
    {
        Console.WriteLine("Driving...");
    }
}

Conclusion​

CS0534 tells you that your class is incomplete.

  1. Check the To-Do List: Identify which abstract methods from the base class are missing.
  2. Option A (Implement): Write the methods using the override keyword.
  3. Option B (Defer): If this class shouldn't implement them yet, mark the class itself as abstract.

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