多种OfType Linq？

Question

我有一个linq查询，选择占位符中的所有文本框，并使用结构将它们添加到列表中。我需要扩展此功能，以采取DropDownList的选定值我很确定我做这个错误，因为当我调试方法列表计数为0.

我自己的猜测是，宣布2 OfType<>()是错误的，但我对linq很新，我不知道如何去做。

任何帮助将会很棒！提前致谢。

这是我到目前为止有：

public struct content 
{ 
    public string name; 
    public string memberNo; 
    public int points; 
    public string carclass; 
} 

List<content> rows = new List<content>(); 

protected void LinkButton_Submit_Attendees_Click(object sender, EventArgs e) 
{ 
List<content> rows = PlaceHolder_ForEntries.Controls.OfType<TextBox>().OfType<DropDownList>() 
     .Select(txt => new 
     { 
      Txt = txt, 
      Number = new String(txt.ID.SkipWhile(c => !Char.IsDigit(c)).ToArray()) 
     }) 
     .GroupBy(x => x.Number) 
     .Select(g => new content 
     { 
      carclass = g.First(x => x.Txt.ID.StartsWith("DropDownlist_CarClass")).Txt.SelectedValue, 
      name = g.First(x => x.Txt.ID.StartsWith("TextBox_Name")).Txt.Text, 
      memberNo = g.First(x => x.Txt.ID.StartsWith("TextBox_MemberNo")).Txt.Text, 
      points = int.Parse(g.First(x => x.Txt.ID.StartsWith("TextBox_Points")).Txt.Text) 
     }) 
     .ToList(); 
} 

下面是一个创建控件的方法。

protected void createcontrols() 
{ 
    int count = 0; 
    if (ViewState["count"] != null) 
    { 
     count = (int)ViewState["count"]; 
    } 
    while (PlaceHolder_ForEntries.Controls.Count < count) 
    { 
     TextBox TextBox_Name = new TextBox(); 
     TextBox TextBox_MemberNo = new TextBox(); 
     TextBox TextBox_Points = new TextBox(); 
     DropDownList DropDownList_CarClass = new DropDownList(); 
     DropDownList_CarClass.Items.Add("Car1"); 
     ... 
     DropDownList_CarClass.Items.Add("Car2"); 
     TextBox_Name.Attributes.Add("placeholder", "Navn"); 
     TextBox_Name.ID = "TextBox_Name" + PlaceHolder_ForEntries.Controls.Count.ToString(); 
     TextBox_Name.CssClass = "input-small"; 
     TextBox_MemberNo.Attributes.Add("placeholder", "Medlemsnr."); 
     TextBox_MemberNo.ID = "TextBox_MemberNo" + PlaceHolder_ForEntries.Controls.Count.ToString(); 
     TextBox_MemberNo.CssClass = "input-small"; 
     TextBox_Points.Attributes.Add("placeholder", "Point"); 
     TextBox_Points.ID = "TextBox_Points" + PlaceHolder_ForEntries.Controls.Count.ToString(); 
     TextBox_Points.CssClass = "input-small"; 
     PlaceHolder_ForEntries.Controls.Add(TextBox_Name); 
     PlaceHolder_ForEntries.Controls.Add(TextBox_MemberNo); 
     PlaceHolder_ForEntries.Controls.Add(DropDownList_CarClass); 
     PlaceHolder_ForEntries.Controls.Add(TextBox_Points); 
     PlaceHolder_ForEntries.Controls.Add(new LiteralControl("<br />")); 
    } 
} 

Answer 1

可以使用Where和检查类型的对象is的实例！

List<content> rows = PlaceHolder_ForEntries.Controls.Cast<Control>().Where(c => c is TextBox || c is DropDownList) 
     .Select(txt => new 
     { 
      Txt = txt, 
      Number = new String(txt.ID.SkipWhile(c => !Char.IsDigit(c)).ToArray()) 
     }) 
     .GroupBy(x => x.Number) 
     .Select(g => new content 
     { 
      carclass = g.First(x => x.Txt.ID.StartsWith("DropDownlist_CarClass")).Txt.SelectedValue, 
      name = g.First(x => x.Txt.ID.StartsWith("TextBox_Name")).Txt.Text, 
      memberNo = g.First(x => x.Txt.ID.StartsWith("TextBox_MemberNo")).Txt.Text, 
      points = int.Parse(g.First(x => x.Txt.ID.StartsWith("TextBox_Points")).Txt.Text) 
     }) 
     .ToList(); 

Answer 2

你的问题是在OfType<>().OfType<>()你与不同类型的

Answer 3

AppDeveloper is right过滤两次。 OfType<T>过滤除T以外的所有类型的对象;所以通过过滤两次，可以有效地消除列表中的所有对象。

如果你想换这个逻辑（过滤所有，但类型从列表）弄成可重复使用的，什么也没有阻止你实现自己的扩展方法：

using System.Collections; 

public static class EnumerableExtensions 
{ 
    public static IEnumerable OfType<T1, T2>(this IEnumerable source) 
    { 
     foreach (object item in source) 
     { 
      if (item is T1 || item is T2) 
      { 
       yield return item; 
      } 
     } 
    } 
} 

包含上述类的项目将允许你写这样的代码在你的应用程序：

var textBoxesAndDropDowns = controls.OfType<TextBox, DropDownList>(); 

要了解更多关于扩展方法，请参阅the MSDN article on the subject。

请注意，由于上面的“允许”两种不同类型的扩展方法，结果仍然是一个非泛型的IEnumerable序列。如果你想结果视为一个通用序列（例如，IEnumerable<Control>），我会建议使用Cast<T>扩展方法：

var filteredControls = controls.OfType<TextBox, DropDownList>().Cast<Control>(); 

Answer 4

我还没有仔细阅读的问题，但是从标题意味着什么，你可以实现以下行为：

var collection = new object[] { 5, "4545", 'd', 54.5 , 576 }; 

var allowedTypes = new[] { typeof(string), typeof(int) }; 
var result = collection 
.Where(item => allowedTypes.Contains(item.GetType())); 

看到它的行动here。

Answer 5

注意到@Shimmys答案为扩展方法：

/// <param name="wantedTypes">--- Sample: --- new Type[] { typeof(Label), typeof(Button) }</param> 
public static IEnumerable OfTypes(this IEnumerable collection, Type[] wantedTypes) 
{ 
    if (wantedTypes == null) 
     return null; 
    else 
     return collection.Cast<object>().Where(element => wantedTypes.Contains(element.GetType())); 
} 

用法：

// List of 3 different controls 
List<object> controls = new List<object>(new object[] { new Label(), new Button(), new TextBox() }); 

// Get all labels and buttons 
var labelsAndButtons = controls.OfTypes(new Type[] { typeof(Label), typeof(Button) });