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当匿名类型遇上Distinct
首先定义一个简单类，并重写ToString方法。
public class CommidityFilter { public string Property { get; set; } public string Characterist { get; set; } public override string ToString() { return string.Format("Property:{0},Characterist:{1}", this.Property, this.Characterist); } }
然后手动生成一个IEnumerable<CommidityFilter>集合。
private static IEnumerable<CommidityFilter> GetCommidityFilters() { var result = new List<CommidityFilter> { new CommidityFilter {Property = "Size",Characterist = "L"}, new CommidityFilter {Property = "Size",Characterist = "L"}, new CommidityFilter {Property = "Size",Characterist = "XL"}, new CommidityFilter {Property = "Color",Characterist = "Red"}, new CommidityFilter {Property = "Color",Characterist = "Yellow"}, new CommidityFilter {Property = "Color",Characterist = "Red"} }; return result; }
现在要做的是对整个集合进行过滤，去掉重复的CommidityFilter，通常都会用Distinct扩展方法。要对CommidityFilter集合去掉重复项，一共有两种方法。
1：重写CommidityFilter的Equals、GetHashCode方法。
2：Distinct方法指定一个实现了IEqualityComparer接口的对象。
这里我们采用第二种方法，首先来实现CommidityFilterComparer
public class CommidityFilterComparer : IEqualityComparer<CommidityFilter> { public bool Equals(CommidityFilter x, CommidityFilter y) { if (x == null || y == null) return false; return String.Compare(x.Property, y.Property) == 0 && String.Compare(x.Characterist, y.Characterist) == 0; } public int GetHashCode(CommidityFilter obj) { return obj.Property.GetHashCode() ^ obj.Characterist.GetHashCode(); } }
然后实现去掉重复项的代码：
var result = GetCommidityFilters();var filters = result.Distinct(new CommidityFilterComparer()).ToArray();Array.ForEach(filters, Console.WriteLine);
输出的结果如下：
Property：Size,Characterist:L
Property：Size,Characterist:XL
Property：Size,Characterist:Red
Property：Size,Characterist:Yellow
上面完美的实现了想要的结果，但是开发经常遇到的情况是GetCommidityFilters方法返回的集合中的CommidityFilter可能不只是Property，Characterist两个属性，比方还有其他的OtherProperty属性。而前端的ViewModel只需要去掉重复项后Property，Characterist两个属性。在这种情况下，通常会选择用匿名类型。现在来重新定义下CommidityFilter类、以及GetCommidityFilters方法。
public class CommidityFilter { public string Property { get; set; } public string Characterist { get; set; } public string OtherProperty { get; set; } public override string ToString() { return string.Format("Property:{0},Characterist:{1}", this.Property, this.Characterist); } }
private static IEnumerable<CommidityFilter> GetCommidityFilters() { var result = new List<CommidityFilter> { new CommidityFilter {Property = "Size",Characterist = "L",OtherProperty = "A"}, new CommidityFilter {Property = "Size",Characterist = "L",OtherProperty = "B"}, new CommidityFilter {Property = "Size",Characterist = "XL",OtherProperty = "C"}, new CommidityFilter {Property = "Color",Characterist = "Red",OtherProperty = "D"}, new CommidityFilter {Property = "Color",Characterist = "Yellow",OtherProperty = "E"}, new CommidityFilter {Property = "Color",Characterist = "Red",OtherProperty = "F"} }; return result; }
接下来，再来实现去掉重复项的代码。
var result = GetCommidityFilters(); var filters = result.Select(e => new { Property = e.Property, Characterist = e.Characterist }).Distinct().ToArray(); Array.ForEach(filters, Console.WriteLine);
输出的结果如下：
{Property = Size,Characterist = L}
{Property = Size,Characterist = XL}
{Property = Size,Characterist = Red}
{Property = Size,Characterist = Yellow}
在上面实现的去重复项代码中，并没有为Distinct扩展方法指定一个实现了IEqualityComparer接口的对象，还是很完美的去掉的重复项。这是为什么呢？只能借助于IL DASM工具看个究竟了。如下图所示：
原来C#编译器会在背后默默的给所有的匿名类型重写Equals，GetHashCode,ToString三个方法，也就是说对匿名类型的集合使用Distinct过滤重复项，默认就是上面提到的第一种方法。
2014年就要过去了，我的2014相比2013年来说过的有点平庸，在最后一天才写了这年的第一篇随笔，希望2015年，我能过得轰轰烈烈点。
当匿名类型遇上Distinct