public class MyBindingSource : BindingSource
{

    private MethodInfo MyMethod= null;

    protected override void OnBindingComplete(BindingCompleteEventArgs e)
    {
         this.MyMethod = GetMyMethod();
         //MyMethod is not null here
    }

    void UseMyMethod (object value)
    {
        MyMethod.Invoke(SomeObject, new object[] { value });
        //MyMethod is null here, exception thrown.
    }

}

public class MyBindingSource : BindingSource
{
    private MethodInfo _myMethod = null;

    private MethodInfo MyMethod
    {
        get
        {
            if(_myMethod != null) return _myMethod;

            _myMethod = GetMyMethod();
            return _myMethod;
        }
    }

    protected override void OnBindingComplete(BindingCompleteEventArgs e)
    {
    }

    void UseMyMethod (object value)
    {
        MyMethod.Invoke(SomeObject, new object[] { value });
    }
}