在最新發布的v23.1版本中，DevExpress WinForms Lookup Editor（查找編輯器）引入了一個非常受歡迎的功能——多項選擇。在這種新的選擇模式下，Lookup Editor顯示一個帶有復選框的列，用戶可以使用鼠標或鍵盤選擇查找項。

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啟用多項選擇

使用EditValueType屬性來啟用多項選擇，此屬性指定Lookup如何在其EditValue屬性中存儲所選值。可用的選項包括：

• LookUpEditValueType.ValueList —Lookup將選擇的值存儲為對象(List<object>)。
• LookUpEditValueType.CSVString — Lookup將選定的值存儲為帶有逗號分隔值的字符串。

下面的示例演示如何激活多項選擇，將查找的EditValue屬性設置為一個帶有id的列表，以便在應用程序啟動時選擇相應的產品。

using System.Windows.Forms;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using DevExpress.XtraEditors;
using DevExpress.XtraEditors.Repository;

public partial class Form1 : XtraForm {
public Form1() {
InitializeComponent();
lookUpEdit1.Properties.DataSource = ProductA.GetList();
lookUpEdit1.Properties.DisplayMember = "Name";
lookUpEdit1.Properties.ValueMember = "ID";
lookUpEdit1.Properties.EditValueType = LookUpEditValueType.ValueList;
lookUpEdit1.EditValue = new List<object>() {0, 1, 4};
}
}
public class ProductA {
int id;
public ProductA(int id) {
this.id = id;
}
[Display(Order = -1)]
public int ID {
get { return id; }
}
[Display(ShortName = "Bakery & Desserts")]
public string Name { get; set; }
[DisplayFormat(DataFormatString = "c2")]
public double Price { get; set; }
public static List<ProductA> GetList() {
return new List<ProductA>() {
new ProductA(0){ Name = "Butter Cake", Price = 56.99 },
new ProductA(1){ Name = "Chocolate Pie ", Price = 89.99 },
new ProductA(2){ Name = "Frozen Cookie Dough", Price = 54.99 },
new ProductA(3){ Name = "Truffie Cake", Price = 59.99 },
new ProductA(4){ Name = "Original Apple Pie", Price = 59.99 }
};
}
}

將選定狀態綁定到數據

Lookup Editor（查找編輯器）可以保存有關數據源字段中所選項的信息，使用CheckBoxSelectorName屬性指定包含所選項信息的字段名。如果此字段包含非布爾值類型，您還應該處理以下事件來根據需要 "convert" 字段值：

如何綁定到布爾數據字段

下面的示例演示了如何將選擇綁定到“Selected”字段(帶有布爾值)：

public partial class Form1 : XtraForm {
public Form1() {
InitializeComponent();
lookUpEdit2.Properties.DataSource = ProductB.GetList();
lookUpEdit2.Properties.DisplayMember = "Name";
lookUpEdit2.Properties.ValueMember = "ID";
lookUpEdit2.Properties.CheckBoxSelectorMember = "Selected";
lookUpEdit2.Properties.EditValueType = LookUpEditValueType.ValueList;
lookUpEdit2.EditValue = new List<object>() {0, 1};
}
}
public class ProductB {
int id;
public ProductB(int id) {
this.id = id;
}
[Display(Order = -1)]
public int ID {
get { return id; }
}
[Display(ShortName = "Bakery & Desserts")]
public string Name { get; set; }
[DisplayFormat(DataFormatString = "c2")]
public double Price { get; set; }
public int InStock { get; set; }
[Display(ShortName = "Add to Order")]
public bool Selected { get; set; }
public static List<ProductB> GetProductList() {
return new List<ProductB>() {
new ProductB(0){ Name = "Butter Cake", Price = 56.99, InStock = 50 },
new ProductB(1){ Name = "Chocolate Pie ", Price = 89.99, InStock = 32 },
new ProductB(2){ Name = "Frozen Cookie Dough", Price = 54.99, InStock = 0 },
new ProductB(3){ Name = "Truffie Cake", Price = 59.99, InStock = 42 },
new ProductB(4){ Name = "Original Apple Pie", Price = 59.99, InStock = 0}
};
}
}

從下面的截圖中可以看到，lookup創建了一個選擇器列(Add to Order)，并將其綁定到“Selected”數據字段。

如何綁定到集合屬性

如果將EditValueType屬性設置為LookUpEditValueType.ValueList，則可以將查找的EditValue屬性綁定到只讀集合類型屬性，這個操作是由 設置控制的(默認情況下是啟用的)。

using System.Windows.Forms;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using DevExpress.XtraEditors;
using DevExpress.XtraEditors.Repository;

public partial class Form1 : XtraForm {
List<Item> orderItems;
List<Order> orders;
public Form1() {
InitializeComponent();
orders = new List<Order>(){
new Order(10295),
new Order(10296),
new Order(10297)
};
teOrder.DataBindings.Add(new Binding("EditValue", orders, "ID"));
dataNavigator1.DataSource = orders;

orderItems = new List<Item>() {
new Item(){ ID = 0, ItemName = "Butter Cake", Price = 56.99 },
new Item(){ ID = 1, ItemName = "Chocolate Pie", Price = 89.99},
new Item(){ ID = 2, ItemName = "Frozen Cookie Dough", Price = 54.99},
new Item(){ ID = 3, ItemName = "Truffie Cake", Price = 59.99 },
new Item(){ ID = 4, ItemName = "Original Apple Pie", Price = 59.99 }
};
lookupOrderItems.Properties.DataSource = orderItems;
lookupOrderItems.Properties.DisplayMember = "ItemName";
lookupOrderItems.Properties.ValueMember = "ID";
lookupOrderItems.Properties.EditValueType = LookUpEditValueType.ValueList;
lookupOrderItems.DataBindings.Add(new Binding("Editvalue", orders, "Items"));
}
}

public class Order {
int id;
public Order(int id) {
this.id = id;
Items = new HashSet<int>();
}
[Display(ShortName = "Order ID")]
public int ID { get { return id; } }
public HashSet<int> Items { get; private set; }
}
public class Item {
public int ID { get; set; }
public string ItemName { get; set; }
public double Price { get; set; }
}

有條件的選擇

使用此選項，您可以阻止用戶根據特定條件選擇項目，處理SelectionChanging事件并將e.Cancel參數設置為true來取消項目選擇。

using DevExpress.XtraEditors.Controls;

public partial class Form1 : XtraForm {
List<ProductB> products;
public Form1() {
InitializeComponent();
//...
lookUpEdit1.Properties.SelectionChanging += Properties_SelectionChanging;
}
private void Properties_SelectionChanging(object sender, PopupSelectionChangingEventArgs e) {
e.Cancel = products[e.RecordIndex].InStock == 0;
}
}

重要提示：WinForms LookUpEdit控件可以選擇多個項目，GridLookUpEdit、TreeListLookUpEdit和SearchLookUpEdit控件不支持此功能。