C#设计模式---单例模式（Singleton Pattern）

一、定义

从“单例”字面意思上理解为一个类只有一个实例。官方定义：确保一个类只有一个实例,并提供一个全局访问点。

二、实现

下面以实现一个日志记录类为例，描述单例模式。

 1 using System;
 2 using System.IO;
 3
 4 namespace Utility
 5 {
 6     public class Logger
 7     {
 8         private static Logger loggerInstance = null;
 9         private static readonly object lockObject = new object();
10
11         private string logFolderName  =@"C:\Temp\LogFiles\FilamentCalibration\";
12
13         private  string logFullPath;
14
15         private Logger(string pLogFolderName = @"C:\Temp\LogFiles\FilamentCalibration\")
16         {
17             logFolderName = pLogFolderName;
18             logFullPath = String.Format(logFolderName + "{0:yyyyMMdd HHmmss} FilamentCal.log", DateTime.Now);
19
20             if (!Directory.Exists(logFolderName))
21             {
22                 Directory.CreateDirectory(logFolderName);
23             }
24         }
25
26         public static Logger GetLoggerInstance(string pLogFolderName = @"C:\Temp\LogFiles\FilamentCalibration\")
27         {
28             if (loggerInstance == null)
29             {
30                 lock (lockObject)
31                 {
32                     if (loggerInstance == null)
33                     {
34                         loggerInstance = new Logger(pLogFolderName);
35                     }
36                 }
37             }
38             return loggerInstance;
39         }
40
41         public void WriteLine(string text)
42         {
43             try
44             {
45                 using (StreamWriter myLogger = File.AppendText(logFullPath))
46                 {
47                     myLogger.WriteLine($"[FilaCal {DateTime.Now:HH:mm:ss.fff]} {text}");
48                 }
49             }
50             catch(Exception err)
51             {
52                 throw new Exception(err.Message);
53             }
54         }
55     }
56 }