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。

using System;
using System.IO;

namespace Utility
{
    public class Logger
    {
        private static Logger loggerInstance = null;
        private static readonly object lockObject = new object();

        private string logFolderName  =@"C:TempLogFilesFilamentCalibration";

        private  string logFullPath;

        private Logger(string pLogFolderName = @"C:TempLogFilesFilamentCalibration")
        {
            logFolderName = pLogFolderName;
            logFullPath = String.Format(logFolderName + "{0:yyyyMMdd HHmmss} FilamentCal.log", DateTime.Now);

            if (!Directory.Exists(logFolderName))
            {
                Directory.CreateDirectory(logFolderName);
            }
        }

        public static Logger GetLoggerInstance(string pLogFolderName = @"C:TempLogFilesFilamentCalibration")
        {
            if (loggerInstance == null)
            {
                lock (lockObject)
                {
                    if (loggerInstance == null)
                    {
                        loggerInstance = new Logger(pLogFolderName);
                    }
                }
            }
            return loggerInstance;
        }

        public void WriteLine(string text)
        {
            try
            {
                using (StreamWriter myLogger = File.AppendText(logFullPath))
                {
                    myLogger.WriteLine($"[FilaCal {DateTime.Now:HH:mm:ss.fff]} {text}");
                }
            }
            catch(Exception err)
            {
                throw new Exception(err.Message);
            }
        }
    }
}