[Self Instance 的寫法] 簡單的 Singleton 寫法 #dotnet #c

main.cs

void Main()
{
	var instance1 = SampleService.Instance;
	var instance2 = SampleService.Instance;
	Console.WriteLine(instance1.WhoAmI().Equals(instance2.WhoAmI()) ? "It's the same instance." : "It's NOT the same instance.");

	Console.WriteLine();

	var instanceWithCtor1 = SampleServiceWithCtor.SelfInstance("Poy Chang");
	var instanceWithCtor2 = SampleServiceWithCtor.SelfInstance("Poy Chang");
	Console.WriteLine(instanceWithCtor1.WhoAmI().Equals(instanceWithCtor2.WhoAmI()) ? "It's the same instance." : "It's NOT the same instance.");
}

public class SampleService
{
	private static SampleService instance;

	public static SampleService Instance
	{
		get { return instance ?? (instance = new SampleService()); }
		set { instance = value; }
	}

	public int WhoAmI()
	{
		Console.WriteLine(instance.GetHashCode());
		return instance.GetHashCode();
	}
}

// 若建構式需要參數可以這樣做
public class SampleServiceWithCtor
{
	private static SampleServiceWithCtor instance;
	private string Name;
	public SampleServiceWithCtor(string name)
	{
		Name = name;
	}

	public static SampleServiceWithCtor SelfInstance(string name = null)
	{
		return instance ?? (instance = new SampleServiceWithCtor(name));
	}

	public int WhoAmI()
	{
		Console.WriteLine($"{instance.GetHashCode()}, {Name}");
		return instance.GetHashCode();
	}
}