System.MissingMethodException – Method ‘xyz’ not found

The System.MissingMethodException with the message “Method ‘xyz’ not found” occurs in C# when you attempt to access or invoke a method that does not exist in the specified type. This typically happens when using reflection, dynamic binding, or when there is a mismatch between the method name or signature.

Common Causes and Solutions

1. Incorrect Method Name:
   If you provide an incorrect method name when using reflection or dynamic binding, this exception will be thrown.

   public class Example
   {
       public void PrintMessage(string message) => Console.WriteLine(message);
   }

   var method = typeof(Example).GetMethod("PrintMessages"); // Incorrect method name
   method.Invoke(new Example(), new object[] { "Hello" }); // MissingMethodException

Fix: Ensure the method name is correct and matches the actual method.

   var method = typeof(Example).GetMethod("PrintMessage"); // Correct method name
   method.Invoke(new Example(), new object[] { "Hello" }); // Works correctly

2. Incorrect Method Signature:
   If the method exists but the signature (parameters or return type) does not match, this exception can occur.

   public class Example
   {
       public void PrintMessage(string message) => Console.WriteLine(message);
   }

   var method = typeof(Example).GetMethod("PrintMessage", new[] { typeof(int) }); // Incorrect parameter type
   method.Invoke(new Example(), new object[] { 123 }); // MissingMethodException

Fix: Ensure the method signature matches exactly.

   var method = typeof(Example).GetMethod("PrintMessage", new[] { typeof(string) }); // Correct parameter type
   method.Invoke(new Example(), new object[] { "Hello" }); // Works correctly

3. Overloaded Methods:
   If there are multiple overloaded methods and you do not specify the correct one, this exception can occur.

   public class Example
   {
       public void PrintMessage(string message) => Console.WriteLine(message);
       public void PrintMessage(string message, int count) => Console.WriteLine($"{message} {count}");
   }

   var method = typeof(Example).GetMethod("PrintMessage"); // Ambiguous method
   method.Invoke(new Example(), new object[] { "Hello" }); // MissingMethodException

Fix: Specify the exact method by providing parameter types.

   var method = typeof(Example).GetMethod("PrintMessage", new[] { typeof(string) }); // Correct method
   method.Invoke(new Example(), new object[] { "Hello" }); // Works correctly

4. Using dynamic:
   When using dynamic, if the method does not exist on the object, this exception can occur at runtime.

   dynamic obj = new Example();
   obj.PrintMessages("Hello"); // MissingMethodException – Method does not exist

Fix: Ensure the method exists on the object.

   obj.PrintMessage("Hello"); // Correct method name

5. Version Mismatch or Missing Assembly:
   If the method exists in a different version of the assembly or the assembly is missing, this exception can occur. Fix: Ensure the correct version of the assembly is referenced and the method exists.
6. Private or Non-Public Methods:
   If the method is private or non-public and you attempt to access it without proper reflection flags, this exception can occur.

   public class Example
   {
       private void PrintMessage(string message) => Console.WriteLine(message);
   }

   var method = typeof(Example).GetMethod("PrintMessage"); // MissingMethodException – Private method

Fix: Use BindingFlags to access non-public methods.

   var method = typeof(Example).GetMethod("PrintMessage", BindingFlags.NonPublic | BindingFlags.Instance);
   method.Invoke(new Example(), new object[] { "Hello" }); // Works correctly

7. Incorrect Use of Generics:
   If you attempt to invoke a generic method without specifying the correct type arguments, this exception can occur.

   public class Example
   {
       public void PrintMessage<T>(T message) => Console.WriteLine(message);
   }

   var method = typeof(Example).GetMethod("PrintMessage"); // MissingMethodException – Generic method

Fix: Specify the type arguments for the generic method.

   var method = typeof(Example).GetMethod("PrintMessage").MakeGenericMethod(typeof(string));
   method.Invoke(new Example(), new object[] { "Hello" }); // Works correctly