Linq OrderBy不对List< T>进行排序.如何对列表进行排序? [英] Linq OrderBy does not sort a List<T>. How do I sort the list?

问题描述

OrderBy子句有问题，对排序没有任何影响.我已经在调试器中进行了遍历，并确保了这种情况是命中了代码的排序行，并在未应用排序依据之后检查结果.

Having issues with the OrderBy clause not having any impact on the sort. I have walked through this in the debugger and insuring this is a case that the sort line of the code is being hit and reviewing the results after it the order by has not been applied.

public static IEnumerable<DDLOptions<TValueType>> GetDDLOptionsViewModel<TClass, TValueType>(
            IEnumerable<TClass> list, 
            Func<TClass, TValueType> value, 
            Func<TClass, string> displayText,
            bool sort = true
        )
        {
            List<DDLOptions<TValueType>> ddlOptions;

            ddlOptions = list.Select(
                l => new DDLOptions<TValueType>
                        {
                            Value = value(l),
                            DisplayText = displayText(l)
                        }
                    ).ToList();  <========== Works if I put the Order By here.

            if (sort)
            {
                ddlOptions.OrderBy(l => l.DisplayText); <===== Does NOT work here.
            }

            return ddlOptions;
        }

推荐答案

OrderBy 返回可以执行排序的查询:它不会修改原始列表(而类似List<T>.Sort会修改原始内容)

OrderBy returns a query that would perform the ordering: it does not modify the original list (whereas something like List<T>.Sort would modify the original)

相反，请尝试以下操作:

Instead try something like:

ddlOptions = ddlOptions.OrderBy(l => l.DisplayText).ToList();

您可能想尝试使用ddlOptions的类型，或者在我们执行可能超出必要的ToList时，在何处/如何返回数据，但这可能是次要的/没有问题的无论如何，这种情况.

You might want to play around with the type of ddlOptions or where/how you return the data as we're doing an extra ToList than probably necessary, but that's probably a minor/non-issue for this case anyway.

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