C#•2y ago

Issue setting up Singleton

In my project, I have a Singleton which I want to use in certain files. When I try to implement it in one I get an error. First, let me show some code: The singleton:

public sealed class RegularPuzzleSingleton : ISingleton
    {
        private const int TrimLength = 13;
        private Dictionary<string, Type> _regularTypes;
        public IRegularPuzzle RegularPuzzle { get; private set; }

        private RegularPuzzleSingleton() 
        {
            GetRegularTypes();
        }

        public static RegularPuzzleSingleton _instance;

        public static RegularPuzzleSingleton GetInstance()
        {
            _instance ??= new RegularPuzzleSingleton();

            return _instance;
        }

        public void GetRegularTypes()
        {
            var interfaceType = typeof(IRegularPuzzle);
            var implementingTypes = AppDomain.CurrentDomain
                                    .GetAssemblies()
                                    .SelectMany(a => a.GetTypes())
                                    .Where(type => interfaceType.IsAssignableFrom(type)
                                            && !type.IsAbstract
                                            && !type.IsInterface);

            foreach (var type in implementingTypes)
            {
                string name = type.Name.ToLower()[..(type.Name.Length - TrimLength)];
                _regularTypes[name] = type;
            }
        }

        public bool IsRegularType(string extension)
        {
            if (_regularTypes.TryGetValue(extension, out Type? regular) && regular != null)
            {
                RegularPuzzle = (IRegularPuzzle)Activator.CreateInstance(regular);
                return true;
            }

            return false;
        }
    }

public sealed class RegularPuzzleSingleton : ISingleton
    {
        private const int TrimLength = 13;
        private Dictionary<string, Type> _regularTypes;
        public IRegularPuzzle RegularPuzzle { get; private set; }

        private RegularPuzzleSingleton() 
        {
            GetRegularTypes();
        }

        public static RegularPuzzleSingleton _instance;

        public static RegularPuzzleSingleton GetInstance()
        {
            _instance ??= new RegularPuzzleSingleton();

            return _instance;
        }

        public void GetRegularTypes()
        {
            var interfaceType = typeof(IRegularPuzzle);
            var implementingTypes = AppDomain.CurrentDomain
                                    .GetAssemblies()
                                    .SelectMany(a => a.GetTypes())
                                    .Where(type => interfaceType.IsAssignableFrom(type)
                                            && !type.IsAbstract
                                            && !type.IsInterface);

            foreach (var type in implementingTypes)
            {
                string name = type.Name.ToLower()[..(type.Name.Length - TrimLength)];
                _regularTypes[name] = type;
            }
        }

        public bool IsRegularType(string extension)
        {
            if (_regularTypes.TryGetValue(extension, out Type? regular) && regular != null)
            {
                RegularPuzzle = (IRegularPuzzle)Activator.CreateInstance(regular);
                return true;
            }

            return false;
        }
    }

13 Replies

electronic heartbreak.OP•2y ago

Startup:

private IServiceProvider ServiceProvider { get; set; }

        public Startup()
        {
            InitServiceCollection();

            fileReader = new FileReader.FileReader(ServiceProvider.GetService<ISingleton>());
            baseSudokuFactory = new();
        }

        private void InitServiceCollection()
        {
            var services = new ServiceCollection();
            services.AddSingleton<ISingleton, RegularPuzzleSingleton>();
            services.AddTransient<IDisplay, Display>(); 

            ServiceProvider = services.BuildServiceProvider();
        }

private IServiceProvider ServiceProvider { get; set; }

        public Startup()
        {
            InitServiceCollection();

            fileReader = new FileReader.FileReader(ServiceProvider.GetService<ISingleton>());
            baseSudokuFactory = new();
        }

        private void InitServiceCollection()
        {
            var services = new ServiceCollection();
            services.AddSingleton<ISingleton, RegularPuzzleSingleton>();
            services.AddTransient<IDisplay, Display>(); 

            ServiceProvider = services.BuildServiceProvider();
        }

FileReader:

 private readonly ISingleton _singleton;

        public FileReader(ISingleton singleton)
        {
            _singleton = singleton;
        }

 private readonly ISingleton _singleton;

        public FileReader(ISingleton singleton)
        {
            _singleton = singleton;
        }

When i try to run this;

System.InvalidOperationException: 'A suitable constructor for type 'DPAT.LOGIC.FileReader.Extensions.RegularPuzzleSingleton' could not be located. Ensure the type is concrete and services are registered for all parameters of a public constructor.'

System.InvalidOperationException: 'A suitable constructor for type 'DPAT.LOGIC.FileReader.Extensions.RegularPuzzleSingleton' could not be located. Ensure the type is concrete and services are registered for all parameters of a public constructor.'

at line:

            fileReader = new FileReader.FileReader(ServiceProvider.GetService<ISingleton>());

The thing is, is that a singleton normally wont need a public ctor.

cap5lut•2y ago

and services are registered for all parameters of a public constructor

it needs a public constructor, if it has no constructor at all it implicitly has a public constructor added by the compiler

electronic heartbreak.OP•2y ago

Yeah i added that one and that works. It still feels like I break something. By not having that private constructor. (I would also think that the getInstance is not needed anymore)

cap5lut•2y ago

well if u really want to force the private constructor u would have to register the singleton using a factory method: services.AddSingleton<ISingleton, RegularPuzzleSingleton>(serviceProvider => RegularPuzzleSingleton.GetInstance());

electronic heartbreak.OP•2y ago

Okay, but wont the AddSingleton do the Singleton part for me already?

cap5lut•2y ago

yep usually its bad practice to design a class so that it is enforced to be a singleton let the consumer of the class decide how many instances they want ;p

electronic heartbreak.OP•2y ago

😩 I currently live in a design pattern hell. We need to make a sudoku game with building design patterns I basically wanted a singleton so i can create the class above just once and use it everywere (only 2 places)

cap5lut•2y ago

registering the class as singleton in the DI container is totally fine. u simply decided then that u only need that one "global" instance but because u enforce it via private constructor + static getter method, u are forced to and couldnt for example use an instance per scope

electronic heartbreak.OP•2y ago

So, leaving the private ctor and getInstance out it is fine?

cap5lut•2y ago

yeah i would get rid of the private constructor and GetInstance and keep registering it as services.AddSingleton<ISingleton, RegularPuzzleSingleton>();

electronic heartbreak.OP•2y ago

Thank you so much!!

cap5lut•2y ago

glad i could help 😄 i would also not call the interface ISingleton, give it a name that describes what that service is

electronic heartbreak.OP•2y ago

True, I just named that for now and when I discussed it with my duo we gonna refactor it.

Gaming

Programming

Issue setting up Singleton