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C#引用转换
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| ## 引用转换 | |
| 一个对象的引用可以隐式地转换到其父类的引用(UpCast) | |
| 转换至子类的引用则为显示转换(DownCast) | |
| 有序列表引用转换：创建了一个新的引用，它也能指向该对象 | |
| ## UpCast | |
| 从子类的引用创建父类的引用 | |
| ``` | |
| Stock msft = new Stock(); | |
| Asset a = msft; //UpCasts | |
| ``` | |
| 变量a此时指向同一个对象 | |
| ``` | |
| if (a == msft) //true | |
| ``` | |
| 尽管a与msft指向同一个对象，但是变量a较于msft，可视范围更小 | |
| ``` | |
| a.Name; // Ok | |
| a.SharePassWord; // Error: SharePassWord Undefined | |
| ``` | |
| 原因分析：父类并不具有该属性，所以无法访问 | |
| ## DownCast | |
| ``` | |
| Stock msft = new Stock(); | |
| Asset a = msft; | |
| Stock s = Stock(a); | |
| a.SharePassWord; // No Error | |
| s == a; // True | |
| s == msft; // True | |
| ``` | |
| 和向上转换一样，只涉及到引用，底层的对象不会受到影响 | |
| 需要显示转换，因为可能会失败 | |
| 如果向下转换失败，会抛出InvalidCastException |
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