Singleton的出现,取代了C++中全局变量——这个破坏OO封装性的概念。
使用场所:控制Socket通信,写日志,简单工厂。
实现Singleton的三个要点
1.私有化构造函数
2.保存实例的静态私有变量
3.访问这个实例的公共静态方法
实现如下:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
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![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
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Client端使用:
CSingleton.Instance().Do();
例子1:单件窗体
点一下Menu,弹生一个弹出窗体(实例),在关闭这个新窗体之前,再次点击该Menu,不会再次出现同样的弹出窗体(实例)——Windows系统中的控制面板也是这个原理,永远只有一个。
代码如下:
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
从而,无论在哪里调用Form1,都会得到相同的实例:
Form1.Instance().Show();
——这里要确保Form1_Closed事件中清除窗体实例sf
单件是对类静态函数的一种改进。因为单件可以有子类,可以定义虚函数,具有多态性;静态函数就没有以上特性。
补注:
1.说到私有构造函数,其实还有另两种,保护型构造函数,静态构造函数,可以共存。