綁定到數據源的數據感知控件可以要求顯示附加項。這些項，由控件顯示但不存儲在其底層數據源中，被稱為虛擬或未綁定行。此示例演示如何使用UnboundSource組件實現這些行。

1. 使用lookup editor時經常需要虛擬行，這些行通常需要在其下拉列表中顯示“全部”或“無”等服務項。因此，首先將UnboundSource組件和LookUpEdit控件添加到表單中。

2. 使用UnboundSource組件為lookup editor提供數據。本文將介紹整個過程。以下是您需要做什么的簡要說明。

· 準備外部數據集。對于此示例應用程序，您可以使用填充有簡單實體的列表結構，如下所示：

[C#]

public partial class Form1 : Form {
    public List<Product> Products = new List<Product>();

    public Form1() {
        InitializeComponent();
        Products.AddRange(new Product[] {
            new Product(1, "Item One"),
            new Product (2, "Item Two"),
            new Product(3, "Item Three")});
    }
    
}

public class Product {
    public Product(int ID, string productName) {
        this.ID = ID;
        this.ProductName = productName;
    }

    public int ID { get; set; }
    public string ProductName { get; set; }
}

[VB]

Partial Public Class Form1

    Inherits Form



    Public Products As New List(Of Product)()



    Public Sub New()

        InitializeComponent()

        Products.AddRange(New Product() {

            New Product(1, "Item One"),

            New Product(2, "Item Two"),

            New Product(3, "Item Three")

        })

    End Sub



End Class



Public Class Product

    Public Sub New(ByVal ID As Integer, ByVal productName As String)

        Me.ID = ID

        Me.ProductName = productName

    End Sub



    Public Property ID() As Integer

    Public Property ProductName() As String

End Class

· 將數據字段添加到您的UnboundSource組件。字段名稱必須參考現有的數據集字段。

· 將UnboundSource組件分配給編輯器的RepositoryItemLookUpEditBase.DataSource屬性。

· 指定編輯器的RepositoryItemLookUpEditBase.DisplayMember和RepositoryItemLookUpEditBase.ValueMember屬性。

3. 調用組件的SetRowCount方法來指定“查找”應顯示的項數。通常，您將使用實際數據集行計數作為方法的參數。由于我們需要多個附加行，請使用如下所示的較高值。

[C#]

public const int NotInListItemsCount = 2;
unboundSource1.SetRowCount(Products.Count + NotInListItemsCount);

[VB]

Public Const NotInListItemsCount As Integer = 2
unboundSource1.SetRowCount(Products.Count + NotInListItemsCount)

4. 最后，處理組件的ValueNeeded事件并添加所需的虛擬行。

[C#]

void unboundSource1_ValueNeeded(object sender, DevExpress.Data.UnboundSourceValueNeededEventArgs e) {
    e.Value = GetExtendedListValues(e.RowIndex, e.PropertyName);
}

object GetExtendedListValues(int rowIndex, string propertyName) {
    switch(propertyName) {
        case "ID":
            switch(rowIndex) {
                case 0:
                    return null;
                case 1:
                    return null;
                default:
                    return Products[rowIndex - NotInListItemsCount].ID;
            }
        case "ProductName":
            switch(rowIndex) {
                case 0:
                    return "None";
                case 1:
                    return "All";
                default:
                    return Products[rowIndex - NotInListItemsCount].ProductName;
            }
        default:
            return null;
    }
}

[VB]

Private Sub unboundSource1_ValueNeeded(ByVal sender As Object, ByVal e As DevExpress.Data.UnboundSourceValueNeededEventArgs)
    e.Value = GetExtendedListValues(e.RowIndex, e.PropertyName)
End Sub 

Private Function GetExtendedListValues(ByVal rowIndex As Integer, ByVal propertyName As String) As Object 
    Select Case propertyName
        Case "ID" 
            Select Case rowIndex
                Case 0
                    Return Nothing 
                Case 1
                    Return Nothing 
                Case Else 
                    Return Products(rowIndex - NotInListItemsCount).ID
            End Select 
        Case "ProductName" 
            Select Case rowIndex
                Case 0
                    Return "None" 
                Case 1
                    Return "All" 
                Case Else 
                    Return Products(rowIndex - NotInListItemsCount).ProductName
            End Select 
        Case Else 
            Return Nothing 
    End Select 
End Function

結果如下圖所示：

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