如何返回 TYPED 结果？答案

【问题标题】：How do I returned a TYPED result?如何返回 TYPED 结果？
【发布时间】：2011-04-18 12:11:20
【问题描述】：

我想将Sorted 定义为ErrorProviderMessageCollection 类型，这就是unsortedCollection 的定义。

Dim Sorted As ErrorProviderMessageCollection = From item In unsortedCollection 
                                               Order By item.Control.TabIndex

我该怎么做？

Public Class ErrorProviderMessage Implements IComparable(Of ErrorProviderMessage)

    Private _Message As String
    Private _Control As Control

    Public Sub New(ByVal message As String, ByVal control As Control)
        _Message = message
        _Control = control
    End Sub

    Public ReadOnly Property Message() As String
        Get
            Return _Message
        End Get
    End Property

    Public ReadOnly Property Control() As Control
        Get
            Return _Control
        End Get
    End Property

    Public Function CompareTo(ByVal other As ErrorProviderMessage) As Integer Implements System.IComparable(Of ErrorProviderMessage).CompareTo
        Return Me.Control.TabIndex.CompareTo(other.Control.TabIndex)
    End Function

End Class

Public Class ErrorProviderMessageCollection

    Inherits System.Collections.ObjectModel.Collection(Of ErrorProviderMessage)

End Class

【问题讨论】：

标签： .net vb.net linq

【解决方案1】：

您还可以使用 Lambda 和适当的扩展方法来处理强制转换，例如：

var Sorted = unsortedCollection.OrderBy(i=>i.Control.TabIndex).ToSortedErrorProviderMessageCollection();

以及扩展方法...

public static class ErrorProviderMessageCollectionHelper
{
    public static ErrorProviderMessageCollection ToSortedErrorProviderMessageCollection <T>(this IEnumerable<T> source) where T : ErrorProviderMessage 
    {
        var orderedCollection = new ErrorProviderMessageCollection();
        foreach (var item in source)
        {
            orderedCollection.Add(item);
        }
        return orderedCollection;
    }
}

我不熟悉 VB.NET，所以请提供 C# 中的代码示例。

【讨论】：

我把它改成了这个，但它返回“Nothing”：Dim Sorted As ErrorProviderMessageCollection = TryCast(unsortedCollection.OrderBy(Function(i) i.Control.TabIndex), ErrorProviderMessageCollection)
你能贴出ErrorProviderMessageCollection的代码吗？
好的，你要么需要使用扩展方法/ienumerable helper（请参阅上一篇文章了解stackoverflow.com/questions/100851/…）或诉诸foreach语句，例如foreach (var p in unsortedCollection.OrderBy(i => i.Control.TabIndex)) { Sorted.Add(p); }
如果没有更好的结果，我会尝试使用它，但我的第一个原因是我不应该自己重新创建集合。
好吧，让我知道你过得怎么样。看来这里有很多其他人已经走上了扩展方法路径：stackoverflow.com/questions/1121938/…

【解决方案2】：

唯一的办法就是这样做：

Dim Sorted As ErrorProviderMessageCollection = 
    New ErrorProviderMessageCollection(From item In unsortedCollection 
                                       Order By item.Control.TabIndex)

为此，ErrorProviderMessageCollection 需要一个带有 IEnumerable(Of TypeOfItem) 类型参数的构造函数。

【讨论】：

【解决方案3】：

正如批准的答案中所建议的那样，这很有效。此处显示的工作示例：

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim MyCollection As New ErrorProviderMessageCollection


        If txtLastName.Text.Trim = "" Then
            MyCollection.Add(New ErrorProviderMessage("Last Name required", txtLastName, txtLastName.TabIndex))
        End If

        If txtFirstName.Text.Trim = "" Then
            MyCollection.Add(New ErrorProviderMessage("First Name required", txtFirstName, txtFirstName.TabIndex))
        End If

        Dim Sorted As ErrorProviderMessageCollection = New ErrorProviderMessageCollection(From item In MyCollection Order By item.Control.TabIndex)

        For Each ErrorProviderMessage As ErrorProviderMessage In Sorted
            MessageBox.Show(ErrorProviderMessage.Message & " " & ErrorProviderMessage.Control.TabIndex & " " & ErrorProviderMessage.Control.Name)
        Next

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

End Class


Imports System.ComponentModel

Public Class ErrorProviderMessage

    Private _Message As String
    Private _Control As Control
    Private _TabIndex As Integer

    Public Sub New(ByVal message As String, ByVal control As Control, ByVal tabIndex As Integer)
        _Message = message
        _Control = control
        _TabIndex = tabIndex
    End Sub

    Public ReadOnly Property Message() As String
        Get
            Return _Message
        End Get
    End Property

    Public ReadOnly Property Control() As Control
        Get
            Return _Control
        End Get
    End Property

    Public Property Tabindex() As Integer
        Get
            Return _TabIndex
        End Get
        Set(ByVal value As Integer)
            _TabIndex = value
        End Set
    End Property


End Class


Public Class ErrorProviderMessageCollection

    Inherits System.Collections.ObjectModel.Collection(Of ErrorProviderMessage)

    Public Sub New()

    End Sub

    Public Sub New(ByVal source As IEnumerable(Of ErrorProviderMessage))

        Dim orderedCollection = New ErrorProviderMessageCollection()

        For Each Item As ErrorProviderMessage In source
            Me.Add(Item)
        Next

    End Sub

End Class

【讨论】：