使用Linq如何添加列表项

Question

IEnumerable<ReportFavorite> list = reportService.GetReportFavorites(userId);
ddlReportFavorite.Items.Add()

I don't know how to add the lists to the dropdown using Linq. Thanks.

Answer 1

You an use AddRange method:

 var list = reportService.GetReportFavorites(userId);
 ddlReportFavorite.Items.AddRange(list.ToArray());

Answer 2

Depending on the dropdown control you are using, either of these could work:

If it allows its Items to be set to an IEnumerabe<ReportFavourite> :

ddlReportFavorite.Items = reportService.GetReportFavorites(userId);

If Items implements the AddRange method:

ddlReportFavorite.Items.AddRange(reportService.GetReportFavorites(userId));

Or, if these fail

foreach(var reportFavourite in reportService.GetReportFavorites(userId))
    ddlReportFavorite.Items.Add(reportFavourite);

Neither of these methods is really "using LINQ", because LINQ is not a good tool to do this. LINQ is meant to be side-effect free.

Edit: Your comment suggests that you are using a System.Web.UI.WebControls.DropDownList . In this case, the Items collection only accepts instances ListItem , so you need to create these from your ReportFavourites. Try

foreach(var listItem in reportService.GetReportFavorites(userId)
                                     .Select(r => new ListItem(r.Id, r.Name))
    ddlReportFavorite.Items.Add(listItem);

Here, I assume the combo box should display ReportFavourite.Name and have a value of ReportFavourite.Id. Use your own properties, of course

Answer 3

或者，如果您已经在方法中检查了数据的完整性，则可以简单地说：

ddlReportFavorite.Items.AddRange(reportService.GetReportFavorites(userId));

Answer 4

Previously I put as IEnumerable. Now I changed to IList. It is working fine now. Thanks to all.

    int userId = workContext.CurrentUser.UserID;
    var reportFavoriteList = reportService.GetReportFavorites(userId);
    int count = reportFavoriteList.Count;

    for (int i = 0; i < count; i++)
    {
        ddlReportFavorite.Items.Add(reportFavoriteList[i].FavoriteName);
    }

Answer 5

Since ddlReprotFavorite is an UI control and its Items property represent a set of controls as well you ca n not add directly your business entities instead of use DataSource property which automatically create Items collection from the underlying business entities.

IEnumerable<ReportFavorite> list = reportService.GetReportFavorites(userId);      
ddlReportFavorite.DataSource = list;

Answer 6

The IEnumerable<T> is extended by the method Union<T> which unions two IEnumerable<T> 's. This is the more pretty way, without casting it ToList() .

var reportFavoriteList = reportService.GetReportFavorites(userId);
ddlReportFavorite.Items = ddlReportFavorite.Items.Union(reportFavoriteList);