C# 如何比较可空类型？
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How to compare nullable types?
提问by David_001
I have a few places where I need to compare 2 (nullable) values, to see if they're the same.
我有几个地方需要比较 2 个（可为空的）值，以查看它们是否相同。
I think there should be something in the framework to support this, but can't find anything, so instead have the following:
我认为框架中应该有一些东西来支持这一点，但找不到任何东西，所以改为：
public static bool IsDifferentTo(this bool? x, bool? y)
{
return (x.HasValue != y.HasValue) ? true : x.HasValue && x.Value != y.Value;
}
Then, within code I have if (x.IsDifferentTo(y)) ...
然后，在代码中我有 if (x.IsDifferentTo(y)) ...
I then have similar methods for nullable ints, nullable doubles etc.
然后我对可空整数、可空双精度等有类似的方法。
Is there not an easier way to see if two nullable types are the same?
没有更简单的方法来查看两个可空类型是否相同？
Update:
更新：
Turns out that the reason this method existed was because the code has been converted from VB.Net, where Nothing = Nothing returns false (compare to C# where null == null returns true). The VB.Net code should have used .Equals...instead.
原来这个方法存在的原因是因为代码是从 VB.Net 转换而来的，其中 Nothing = Nothing 返回 false（与 C# 相比，null == null 返回 true）。应该使用 VB.Net 代码.Equals...。
采纳答案by Marc Gravell
C# supports "lifted" operators, so if the type (bool?in this case) is known at compile you should just be able to use:
C# 支持“提升”运算符，因此如果类型（bool?在本例中）在编译时已知，您应该能够使用：
return x != y;
If you need generics, then EqualityComparer<T>.Defaultis your friend:
如果您需要泛型，那么EqualityComparer<T>.Default您的朋友是：
return !EqualityComparer<T>.Default.Equals(x,y);
Note, however, that both of these approaches use the "null == null" approach (contrast to ANSI SQL). If you need "null != null" then you'll have to test that separately:
但是请注意，这两种方法都使用“ null == null”方法（与 ANSI SQL 相对）。如果您需要“ null != null”，那么您必须单独测试：
return x == null || x != y;
回答by Mark Seemann
回答by Anton Gogolev
回答by Randy Minder
回答by Lucero
Just use ==, or .Equals().
只需使用==, 或.Equals()。
回答by Kashif
if (x.Equals(y))
回答by hdd42
I wanted to find how to compare two nullable int on C#, but I always get this link after search, so if someone needs to compare exactly two nullable int, then this can be helpful
我想找到如何在 C# 上比较两个可为空的 int，但我总是在搜索后得到这个链接，所以如果有人需要比较两个可为空的 int，那么这可能会有所帮助
a.GetValueOrDefault(int.MinValue).CompareTo(b.GetValueOrDefault(long.MinValue));
a.GetValueOrDefault(int.MinValue).CompareTo(b.GetValueOrDefault(long.MinValue));
