前言
本篇文章继续探索通过继承实现单例模式的可行方案,这次的方案将采用反射机制隐式创建派生类实例,示例代码为C#。
代码
v1.0
cs
using System.Reflection;
/// <summary>
/// 单例模式基类
/// </summary>
/// <typeparam name="T">单例类型</typeparam>
public abstract class Singleton<T>
where T : class
{
public static T instance => _instance.Value;
static readonly Lazy<T> _instance = new Lazy<T>(Create);
#pragma warning disable CS8603
static T Create()
{
return Activator.CreateInstance(typeof(T),
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance,
null, null, null) as T;
}
#pragma warning restore CS8603
}
测试
单例模式基类
cs
/// <summary>
/// 单例模式基类
/// </summary>
/// <typeparam name="T">单例类型</typeparam>
public abstract class SingletonWithTest<T>
where T : class
{
public static T instance => _instance.Value;
static readonly Lazy<T> _instance = new Lazy<T>(Create);
#pragma warning disable CS8603
static T Create()
{
return Activator.CreateInstance(typeof(T),
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance,
null, null, null) as T;
}
#pragma warning restore CS8603
}
派生类
cs
public class TestA : SingletonWithTest<TestA>
{
public readonly string key;
TestA() { key = "Default A"; }
}
public class TestB : SingletonWithTest<TestB>
{
public readonly string key;
public TestB() { key = "Default B"; }
}
public class TestC : SingletonWithTest<TestC>
{
public readonly string key;
public TestC(string key) { this.key = key; }
}
public class TestD : SingletonWithTest<TestD>
{
public readonly string key;
public TestD() { key = "Default D"; }
public TestD(string key) { this.key = key; }
}
public class TestE : SingletonWithTest<TestE>
{
public readonly string key;
TestE() { key = "Default E"; }
public TestE(string key) { this.key = key; }
}
public class TestF : SingletonWithTest<TestF>
{
public readonly string key = "Default F";
}
测试代码
cs
// ********************************* 线程安全测试:通过 *********************************
Thread t1, t2, t3, t4, t5, t6;
// 打印同一单例的 HashCode 测试:通过
// t1 = new Thread(() => Console.WriteLine("Thread1:" + TestA.instance.GetHashCode()));
// t2 = new Thread(() => Console.WriteLine("Thread2:" + TestA.instance.GetHashCode()));
// t3 = new Thread(() => Console.WriteLine("Thread3:" + TestA.instance.GetHashCode()));
// t4 = new Thread(() => Console.WriteLine("Thread4:" + TestA.instance.GetHashCode()));
// t5 = new Thread(() => Console.WriteLine("Thread5:" + TestA.instance.GetHashCode()));
// t6 = new Thread(() => Console.WriteLine("Thread6:" + TestA.instance.GetHashCode()));
// 同时使用不同单例的测试:通过
t1 = new Thread(() => Console.WriteLine("Thread1:" + TestA.instance.GetHashCode()));
t2 = new Thread(() => Console.WriteLine("Thread2:" + TestB.instance.GetHashCode()));
t3 = new Thread(() => Console.WriteLine("Thread3:" + TestC.instance.GetHashCode())); // 没有无参构造函数,触发异常
t4 = new Thread(() => Console.WriteLine("Thread4:" + TestD.instance.GetHashCode()));
t5 = new Thread(() => Console.WriteLine("Thread5:" + TestE.instance.GetHashCode()));
t6 = new Thread(() => Console.WriteLine("Thread6:" + TestF.instance.GetHashCode()));
t1.Start();
t2.Start();
t3.Start();
t4.Start();
t5.Start();
t6.Start();
t1.Join();
t2.Join();
t3.Join();
t4.Join();
t5.Join();
t6.Join();
优缺点分析
| 优点 | 1.继承实现单例模式; 2.按需加载,延迟初始化; 3.线程安全; 4.可以通过单例基类规范统一标准; 5.派生类的无参构造函数用于初始化; 6.将派生类实例创建权限交由派生类本身决定,通常,为遵循单例模式的原则应向外部关闭通过new关键字显式调用构造函数的权限,但这对派生类而言并非硬性要求; |
缺点 | 1.反射开销; 2.派生类必须具备无参构造函数,且无参构造函数需要向单例基类提供可进行反射访问的权限; |
---|
版本改进
......
系列文章
如果这篇文章对你有帮助,请给作者点个赞吧!