Software pattern

Question

Hello,
Do you know any examples about the basic software patterns?

• SingleTon
• Factory
• static

When is it better to use a static variable, class etc?
When not?
Where are the advantages/disadvantages.
Static is global, not an instantiation.
I but solve everything yet without static.
Maybe there is also a good pattern site with good short examples.
I would be asked why I work so little with static. It's not that clear to me, so I ask here.
The main question is
When do I take what? That there is, is already clear.
What are the criteria for the choice?

Maybe there is a simple explanation. Thank you.

Answer 1

This is how I recommend to use a singleton.

using static System.DateTime;  
namespace WinFormsApp2.Classes;  
  
public sealed class Singleton  
{  
    private static readonly Lazy<Singleton> Lazy =   
        new(() => new Singleton());  
  
    public static Singleton Instance => Lazy.Value;  
    public DateTime DateTime { get; set; }   
    private Singleton()  
    {  
        DateTime = Now;  
    }  
}  

Answer 2

In regards to a static class, if nothing needs instantiating this is a clear reason for a static class. I've not created a class in decades that needed instantiation. Look at extension methods, they need to be in a static class and the extension method must be static.

Simple extension method

internal static class DateOnlyExtensions  
{  
    public static string Formatted(this DateOnly sender) => sender.ToString("MM/dd/yy");  
}  

A static class where we call DataOperations.CategoriesArray() of CategoriesArray() with a static using statement, similar to say DateTime.Now. or Console.WriteLine, we can use a static using statement so not to type everything out (good for some, bad for others)

namespace MenuConsoleApp.Classes  
{  
    public class DataOperations  
    {  
  
        public static Categories[] CategoriesArray() =>   
            JsonConvert.DeserializeObject<List<Categories>>(  
                File.ReadAllText(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "json", "categories.json")))  
                .ToArray();  
  

    }  
}  
  

In regards to Singleton, used for dependency injection for services in Startup.cs and Program.cs which make coding easier.

public void ConfigureServices(IServiceCollection services)  
{  
 services.AddRazorPages();  
 services.AddServerSideBlazor();  
  
 services.AddSingleton<RssNews>();  
}  
  

That's the tip of the iceberg, best to do research and come to your own conclusions.

See also

• Implementing the Singleton Pattern in C#
• Factory pattern