我怎样才能让我的通用比较器（IComparer的）处理空值？ [英] How can I make my generic comparer (IComparer) handle nulls?

问题描述

我想编写一个通用的对象比较器进行排序，但我已经注意到它不处理的实例，其中它的比较值之一为null。当一个对象是空的，我希望它把它等同于空字符串。我试着设置空值的String.Empty但后来我得到了一个错误对象的类型必须为字符串就可以调用的CompareTo（）的时候。

I'm trying to write a generic object comparer for sorting, but I have noticed it does not handle the instance where one of the values it's comparing is null. When an object is null, I want it to treat it the same as the empty string. I've tried setting the null values to String.Empty but then I get an error of "Object must be of type String" when calling CompareTo() on it.

public int Compare(T x, T y)
{
    PropertyInfo propertyInfo = typeof(T).GetProperty(sortExpression);
    IComparable obj1 = (IComparable)propertyInfo.GetValue(x, null);
    IComparable obj2 = (IComparable)propertyInfo.GetValue(y, null);

    if (obj1 == null) obj1 = String.Empty; // This doesn't work!
    if (obj2 == null) obj2 = String.Empty; // This doesn't work!

    if (SortDirection == SortDirection.Ascending)
        return obj1.CompareTo(obj2);
    else
        return obj2.CompareTo(obj1);
}

我是pretty的坚持与此吧！任何帮助将是AP preciated。

I'm pretty stuck with this now! Any help would be appreciated.

推荐答案

您不能把你的 T 为空字符串，除非你的T被有效约束是一个字符串。你的应该采取什么的做的是比较空的计划。如

You cannot treat your T as an empty string unless your T was effectively constrained to being a string. What you should do is have a plan for comparing nulls. Such as

if (obj1 == null && obj2 == null)
   return 0;
else if (obj1 == null)
   return -1;
else if (obj2 == null)
   return 1;
else 
   return obj1.CompareTo(obj2);

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