Question

收到<>信号:

The type arguments for method  System.Linq.Enumerable.Select<TSource,TResult>(System.Collections.Generic.IEnumerable<TSource>, System.Func<TSource,int,TResult>)  cannot be inferred from the usage. Try specifying the type arguments explicitly.

The first method has no problems using a IEnumerable<T>.Select() ? Where is the problem with the 2nd method?

private void GetPupilsForSchoolclass()
{
   ObservableCollection<PupilViewModel> pupilsOC = new ObservableCollection<PupilViewModel>
   (                            _adminRepo.GetPupilsBySchoolclassId(_selectedSchoolclass.SchoolclassId).Select(p => new       PupilViewModel(p, _adminRepo))
   );
   SelectedSchoolclass.PupilListViewModel = pupilsOC;
}

private void GetDocumentsForPupil()
{
                ObservableCollection<Document> documentsOC = new ObservableCollection<Document>();
                IEnumerable<Document> documents = _docRepo.GetDocumentsByPupilId(_selectedPupil.Id);
                documents.Select(doc => documentsOC.Add(doc));
                SelectedPupil.Documents.DocumentList = documentsOC;
}

Answer 1

documentsOC.Add returns void.
It doesn t make any sense (and is impossible) to write .Select<Something, void>(...).

你试图做的事情首先不能奏效;Select<>/code>是zy,在你列举结果之前没有叫你。



您应定期使用<条码>。

Answer 2

Error似乎是当你从收集中挑选物品时,就没有填写返回声明。

例:

collection = nonLabors.Select(item =>
                {
                    item.Travel_Miles = item.Travel_Miles_Original != null ? decimal.Parse(item.Travel_Miles_Original) : 0;
                    return item;
                }).ToList();

Answer 3

http://www.un? 如果是,没有办法预测到<代码>Func<> - only to an Action<T> - and Select想要Func<>。

Answer 4

<代码>的返回类型是什么? ObservableCollection<Document> 添加。通常,<代码>Add方法回归无效。您可以不使用LINQSelect为所有内容执行程序,但只履行一种回报某种功能(/Select<>/code>的回报值来自何处?) 相反,可以使用LINQForEach或C# foreach loop。

Answer 5

选址为nota 替代 for。而是使用:

ObservableCollection<Document> documentsOC = new ObservableCollection<Document>();
IEnumerable<Document> documents = _docRepo.GetDocumentsByPupilId(_selectedPupil.Id);
foreach(var doc in documents)
{
    documentsOC.Add(doc);
}
SelectedPupil.Documents.DocumentList = documentsOC;

友情链接