Use .NET Reflection with C# to call Private/Protected Methods

Some days ago I needed to write some tests for an old Windows Service. I was not authorized to make any changes in the Code of the Service (and its libraries), so in order to invoke some protected/private method I needed to use the reflection. What follows, is the code I used: nothing complicated, but maybe can save a bit of your time in case you need to achieve the same 🙂

The name of the method I needed to call is “OnStart”.

MethodInfo onStart = typeof(Service).GetMethod("OnStart", BindingFlags.NonPublic | BindingFlags.Instance);

if (onStart != null)
{
       object result = null;
       ParameterInfo[] parameters = onStart.GetParameters();
       object classInstance = Activator.CreateInstance(typeof(Service), null);
 
       var parameterType = parameters[0].ParameterType;
                
       object[] parametersArray = (object[])Activator.CreateInstance(parameterType, 1);
       result = onStart.Invoke(classInstance, parametersArray);
}