IsOrderedBy扩展方法 [英] IsOrderedBy Extension Method

问题描述

在我的一些测试中，我需要检查列表的顺序，做这样的事情。

In some of my tests i need to check the order of Lists and do it something like this

DateTime lastDate = new DateTime(2009, 10, 1);
foreach (DueAssigmentViewModel assignment in _dueAssigments)
{
    if (assignment.DueDate < lastDate)
    {
        Assert.Fail("Not Correctly Ordered");
    }
    lastDate = assignment.DueDate;
}

我想这样做我把它变成一个扩展方法对IEnumerable的到使其可重复使用的。

What i would like to do i turn this into an extension method on IEnumerable to make it reusable.

我inital的想法是这样的。

My inital idea was this

public static bool IsOrderedBy<T, TestType>(this IEnumerable<T> value, TestType initalValue)
{
    TestType lastValue = initalValue;
    foreach (T enumerable in value)
    {
        if(enumerable < lastValue)
        {
            return false;
        }
        lastValue = value;
    }
    return true;
}

这里的ovious问题是你不能compaire仿制值。任何人都可以提出一个解决方法这一点。

The ovious problem here is you cant compaire to generic values. Can anyone suggest a way round this.

干杯
科林

推荐答案

我相信这会令使用类似排序依据方法...

I think it would make more sense to use a method signature similar to the OrderBy method...

public static bool IsOrderedBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
    bool isFirstPass = true;
    TSource previous = default(TSource);

    foreach (TSource item in source)
    {
        if (!isFirstPass)
        {
            TKey key = keySelector(item);
            TKey previousKey = keySelector(previous);
            if (Comparer<TKey>.Default.Compare(previousKey, key) > 0)
                return false;
        }
        isFirstPass = false;
        previous = item;
    }

    return true;
}

您可以使用它这样的：

List<Foo> list = new List<Foo>();
...

if (list.IsOrderedBy(f => f.Name))
   Console.WriteLine("The list is sorted by name");
else
   Console.WriteLine("The list is not sorted by name");

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