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在最新发布的v23.1版本中，DevExpress WinForms Lookup Editor（查找编辑器）引入了一个非常受欢迎的功能——多项选择。在这种新的选择模式下，Lookup Editor显示一个带有复选框的列，用户可以使用鼠标或键盘选择查找项。

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启用多项选择

使用EditValueType属性来启用多项选择，此属性指定Lookup如何在其EditValue属性中存储所选值。可用的选项包括：

• LookUpEditValueType.ValueList —Lookup将选择的值存储为对象(List<object>)。
• LookUpEditValueType.CSVString — Lookup将选定的值存储为带有逗号分隔值的字符串。

下面的示例演示如何激活多项选择，将查找的EditValue属性设置为一个带有id的列表，以便在应用程序启动时选择相应的产品。

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 }
};
}
}

将选定状态绑定到数据

Lookup Editor（查找编辑器）可以保存有关数据源字段中所选项的信息，使用CheckBoxSelectorName属性指定包含所选项信息的字段名。如果此字段包含非布尔值类型，您还应该处理以下事件来根据需要 "convert" 字段值：

• QueryCheckBoxSelectorMemberIsSelected
• SetCheckBoxSelectorMemberValue

如何绑定到布尔数据字段

下面的示例演示了如何将选择绑定到“Selected”字段(带有布尔值)：

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}
};
}
}

从下面的截图中可以看到，lookup创建了一个选择器列(Add to Order)，并将其绑定到“Selected”数据字段。

如何绑定到集合属性

如果将EditValueType属性设置为LookUpEditValueType.ValueList，则可以将查找的EditValue属性绑定到只读集合类型属性，这个操作是由EnableEditValueCollectionEditing 设置控制的(默认情况下是启用的)。

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; }
}

有条件的选择

使用此选项，您可以阻止用户根据特定条件选择项目，处理SelectionChanging事件并将e.Cancel参数设置为true来取消项目选择。

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控件可以选择多个项目，GridLookUpEdit、TreeListLookUpEdit和SearchLookUpEdit控件不支持此功能。

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