Question

我的项目中有一个类，我只想通过构造函数传递一个特定的参数来实例化它，但是当我传递不同的参数时，它应该实例化一个新的。我如何用单例设计模式实现这一目标？或者，如果用单身人士无法实现，可以提出另一种设计模式吗？

<?php
    $arr = [10,20,30,40];
    $sum_total = sum($arr);
    echo "Sum Total: " . $sum_total;
?>

Answer 1

您必须修改_instance变量初始化的方式，使用一个接受您想要传入的参数值的函数。此外，_instance变量不能再是readonly变量{1}}因为它需要在新函数内初始化。

[TestMethod]
public void CreateSingletonInstance()
{
    SiteStructure s = SiteStructure.GetInstance("Abc123");
    Debug.Print(s.Parameter); // outputs Abc123

    SiteStructure s2 = SiteStructure.GetInstance("Is it really a singleton?");
    Debug.Print(s2.Parameter); // outputs Is it really a singleton?

    SiteStructure s3 = SiteStructure.GetInstance("Abc123");
    Debug.Print(s3.Parameter); // outputs Abc123

    Assert.AreNotEqual(s, s2); // Check to make sure they are different instances
    Assert.AreEqual(s, s3); // Check to make sure they are the same instance
}

public sealed class SiteStructure
{
    static Dictionary<string, SiteStructure> _siteStructures = new Dictionary<string, SiteStructure>();
    static object _instance_Lock = new object();
    public static SiteStructure GetInstance(string parameter)
    {
        if (!_siteStructures.ContainsKey(parameter))
        {
            lock (_instance_Lock)
            {
                if (!_siteStructures.ContainsKey(parameter))
                {
                    _siteStructures.Add(parameter, new SiteStructure(parameter));
                }
            }
        }

        return _siteStructures[parameter];
    }

    private SiteStructure(string parameter)
    {
        // Initialize.
        Parameter = parameter;
    }

    public string Parameter { get; set; }
}

Answer 2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var g = SiteStructure.Instance(4);
        }
    }



    public sealed class SiteStructure { 
 public static SiteStructure Instance() 
 { return new SiteStructure();
 }
        public static SiteStructure Instance (int x)
        { return new SiteStructure (x);
        }

 SiteStructure() { }
SiteStructure(int x) { Console.WriteLine("Hello"); }


}

}

如何通过将不同的参数传递给构造函数来允许实例化不同的单例类

2 个答案: