如何在C＃中將Linq Select Enumerable轉換為首選類型？

Question

我有一個ObservableCollection即MobileModel類型的MobileList 。 MobileModel具有MobileModelInfo列表。

我只需要該MobileList MobileModelInfo 。 所以我在方法ExtractFirstMobileList()使用了Linq Select語句。 但是我無法分配列表，它顯示了一個錯誤。

我的C＃源代碼：

public class Mobile
{
    private ObservableCollection<MobileModel> _mobileList;
    public ObservableCollection<MobileModel> MobileList
    {
        get { return _mobileList; }
        set { _mobileList = value; OnPropertyChanged(); }
    }

    public void GetMobile()
    {
        List<MobileModel> mList = new List<MobileModel>();
        List<MobileModelInfo> modList = new List<MobileModelInfo>();
        MobileModel mob = new MobileModel();

        modList.Clear();
        mob.Brand = "Apple";
        modList.Add(new MobileModelInfo { Name = "iPhone 4", Catagory = "Smart Phone", Year = "2011" });
        modList.Add(new MobileModelInfo { Name = "iPhone 5", Catagory = "Smart Phone", Year = "2013" });
        modList.Add(new MobileModelInfo { Name = "iPhone 6", Catagory = "Premium Smart Phone", Year = "2015" });
        mob.Model = new ObservableCollection<MobileModelInfo>(modList);
        mob.OS = "IOS";
        mList.Add(mob);

        mob = new MobileModel();
        modList.Clear();
        mob.Brand = "Samsung";
        modList.Add(new MobileModelInfo { Name = "S4", Catagory = "Smart Phone", Year = "2011" });
        modList.Add(new MobileModelInfo { Name = "S5", Catagory = "Smart Phone", Year = "2013" });
        modList.Add(new MobileModelInfo { Name = "S6", Catagory = "Ultra Smart Phone", Year = "2015" });
        mob.Model = new ObservableCollection<MobileModelInfo>(modList);
        mob.OS = "Android";
        mList.Add(mob);

        mob = new MobileModel();
        modList.Clear();
        mob.Brand = "MicroSoft";
        modList.Add(new MobileModelInfo { Name = "Lumina 9900", Catagory = "Phone", Year = "2011" });
        modList.Add(new MobileModelInfo { Name = "Opera X220", Catagory = "Smart Phone", Year = "2013" });
        mob.Model = new ObservableCollection<MobileModelInfo>(modList);
        mob.OS = "Windows";
        mList.Add(mob);

        mob = new MobileModel();
        modList.Clear();
        mob.Brand = "Sony Ericssion";
        modList.Add(new MobileModelInfo { Name = "S4", Catagory = "Smart Phone", Year = "2011" });
        modList.Add(new MobileModelInfo { Name = "S5", Catagory = "Smart Phone", Year = "2013" });
        modList.Add(new MobileModelInfo { Name = "S6", Catagory = "Ultra Smart Phone", Year = "2015" });
        mob.Model = new ObservableCollection<MobileModelInfo>(modList);
        mob.OS = "Android";
        mList.Add(mob);

        MobileList = new ObservableCollection<MobileModel>(mList);

        ExtractFirstMobileList(MobileList);

    }


    public void ExtractFirstMobileList(ObservableCollection<MobileModel> Source)
    {
        List<MobileModelInfo> mInfo = Source.Select(t=> t.Model);
    }

}

public class MobileModel : Notify
{
    private string _brand = string.Empty;
    private List<MobileModelInfo> _model = new List<MobileModelInfo>();
    private string _os = string.Empty;

    public string Brand
    {
        get { return _brand; }
        set { _brand = value; OnPropertyChanged(); }
    }
    public List<MobileModelInfo> Model
    {
        get { return _model; }
        set { _model = value; OnPropertyChanged(); }
    }

    public string OS
    {
        get { return _os; }
        set { _os = value; OnPropertyChanged(); }
    }
}

public class MobileModelInfo
{
    public string Name { get; set; }
    public string Catagory { get; set; }
    public string Year { get; set; }
}

請協助我將Enumerable轉換為首選類型。

Answer 1

如果要使用所有不同的MobileModelInfo創建扁平化列表，則可以使用SelectMany ：

List<MobileModelInfo> mInfo = Source.SelectMany(t => t.Model).ToList();

但是您的方法稱為ExtractFirstMobileList ，它建議您要每個子列表中的第一項-在這種情況下，可以使用：

List<MobileModelInfo> mInfo = Source.Select(t => t.Model.First()).ToList();

希望這可以幫助

Answer 2

MobileModel類的Model屬性本身就是一個列表。 因此，您使用的選擇查詢將返回MobileModelInfo的集合的集合（返回類型IEnumerable <List <MobileModelInfo >>）

要將其轉換為List <List <MobileModelInfo >>，請在末尾添加.ToList（）。

List<List<MobileModelInfo>> mInfo = Source.Select(t => t.Model).ToList();

Answer 3

如果需要使用LINQ壓縮列表，請在Select()方法之后使用ToList() Select()方法。 另外，請確保您的列表不為空，它存在並且包含超過0個元素