綁定到數(shù)據(jù)源的數(shù)據(jù)感知控件可以要求顯示附加項(xiàng)。這些項(xiàng)，由控件顯示但不存儲在其底層數(shù)據(jù)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(shí)現(xiàn)這些行。

1. 使用lookup editor時(shí)經(jīng)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(wù)項(xiàng)。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(shù)據(jù)。本文將介紹整個(gè)過程。以下是您需要做什么的簡要說明。

· 準(zhǔn)備外部數(shù)據(jù)集。對于此示例應(yīng)用程序，您可以使用填充有簡單實(shí)體的列表結(jié)構(gòu)，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(shù)據(jù)字段添加到您的UnboundSource組件。字段名稱必須參考現(xiàn)有的數(shù)據(jù)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(diào)用組件的SetRowCount方法來指定“查找”應(yīng)顯示的項(xiàng)數(shù)。通常，您將使用實(shí)際數(shù)據(jù)集行計(jì)數(shù)作為方法的參數(shù)。由于我們需要多個(gè)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(jié)果如下圖所示：

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