c# - 将 OrderBy Predicate 中的 Lambda 表达式从 C# 转换为 VB.net

Question

我有以下内容可以根据工作职位对实体进行排序。所需的顺序在另一个数组中定义。在 C# 中，此代码有效:

IEnumerable<CreditObject> query = credits.OrderBy(x =>
{
    for (int i = 0; i < list.Length; i++)
    {
        if (x.Job == list[i])
            return i;
    }
    throw new NotImplementedException("Job not within List");
});

但是我必须将其转换为 VB.net。我读到的等效内容如下所示:

Dim query As IEnumerable(Of CreditObject) = credits.OrderBy(Function(x) 

    For j As Integer = 0 To templ.Length - 1
        If x.Job = templ(j) Then
            Return j
        End If
    Next

End Function)

这不会编译，在 Function(x) 之后给我“预期的表达式”。我做错了什么？

Answer 1

首先，你把它变成一个真正的方法:

public int GetCreditObjectPosition(CreditObject x, List<int> list) {
    for (int i = 0; i < list.Length; i++) {
        if (x.Job == list[i]) {
            return i;
        }
    }
    throw new NotImplementedException("Job not within List");
}

然后，你只要说:

IEnumerable<CreditObject> query =
    credits.OrderBy(x => GetCreditObjectPosition(x, list));

这很容易转换为 VB。

接下来，您重写 GetCreditObjectPosition 以大幅提升性能:

public int GetCreditObjectPosition(CreditObject x, List<int> list) {
    var jobDictionary = 
        list.Select((job, index) => new { Job = job, Index = Index } )
            .ToDictionary(item => item.Job, item => item.Index);
    int position;
    if(!jobDictionary.TryGetValue(x.Job, out position)) {
        throw new Exception("Job not within List");
    }
    return position;
}