转换 IEnumerable到 IEnumerable;
我在尝试使用 C# 中的收益返回功能时收到此错误。该错误出现在 Visual Studio 内部的选择上，我不太明白。在我看来，我将字符串转换为 ListItem，然后将批次作为 IEnumerable 返回。我对收益回报和 IEnumerable 的理解可能很不切实际，因此任何帮助将不胜感激。注释的代码是老式的方法，可以正常工作。
无法隐式转换类型 'System.Collections.Generic.IEnumerable' 到 'System.Web.UI.WebControls.ListItem'
public partial class CloseIncident : System.Web.UI.Page
{
private ClevelandIncidentRepository repo = new ClevelandIncidentRepository();
protected void Page_Load(object sender, EventArgs e)
{
SetDropDown(InitialType, repo.GetMainTypes());
}
private void SetDropDown(DropDownList dropDown, IEnumerable<string> items)
{
dropDown.Items.Clear();
dropDown.Text = string.Empty;
dropDown.Enabled = items.Count() > 0;
dropDown.Items.AddRange(ToListItem(items).ToArray());
}
private IEnumerable<ListItem> ToListItem(IEnumerable<string> results)
{
yield return from result in results
select new ListItem(result);
//List<ListItem> items = new List<ListItem>();
//items.AddRange(from result in results
// select new ListItem(result));
//return items;
}
}
I'm getting this error which while trying to use the yield return feature in C#. The error appears on the select inside visual studio and I don't really understand it. In my mind I'm converting a string to a ListItem and then returning the lot as an IEnumerable. My understanding of yield return and IEnumerable might very well be off the mark so any help would be appreciated. The commented code is the old school way of doing it which does work properly.
Cannot implicitly convert type
'System.Collections.Generic.IEnumerable'
to
'System.Web.UI.WebControls.ListItem'
public partial class CloseIncident : System.Web.UI.Page
{
private ClevelandIncidentRepository repo = new ClevelandIncidentRepository();
protected void Page_Load(object sender, EventArgs e)
{
SetDropDown(InitialType, repo.GetMainTypes());
}
private void SetDropDown(DropDownList dropDown, IEnumerable<string> items)
{
dropDown.Items.Clear();
dropDown.Text = string.Empty;
dropDown.Enabled = items.Count() > 0;
dropDown.Items.AddRange(ToListItem(items).ToArray());
}
private IEnumerable<ListItem> ToListItem(IEnumerable<string> results)
{
yield return from result in results
select new ListItem(result);
//List<ListItem> items = new List<ListItem>();
//items.AddRange(from result in results
// select new ListItem(result));
//return items;
}
}
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评论（3）
您不需要
yield return from ...而只需return from ...或者您可以：或者甚至摆脱这个函数并且：
You don't need to
yield return from ...but simplyreturn from ...or you could:or even get rid of this function and:
yield return 应该引用单个 ListItem，当迭代 IEnumerable 时，该 ListItem 将以“惰性”方式返回。您的 linq 表达式的类型为 IEnumerable，因此存在不匹配。
yield return should refer to a single ListItem which would be returned in a 'lazy' way when the IEnumerable is iterated. Your linq expression is of type IEnumerable so there is a mismatch.