[DXCategory("Data")]
public LookUpColumnInfoCollection Columns { get; }

<DXCategory("Data")>
Public ReadOnly Property Columns As LookUpColumnInfoCollection

// Form.Load event (recommended)
private void Form1_Load(object sender, EventArgs e) {
    //. . .
    lookUpEdit1.Properties.PopulateColumns();
    lookUpEdit1.Properties.Columns.Add(new DevExpress.XtraEditors.Controls.LookUpColumnInfo("Code", "Added in code", 100));
}

// form constructor
public Form1() {
    InitializeComponent();
    //. . .
    lookUpEdit1.Properties.ForceInitialize();
    lookUpEdit1.Properties.PopulateColumns();
    lookUpEdit1.Properties.Columns.Add(new DevExpress.XtraEditors.Controls.LookUpColumnInfo("Code", "Added in code", 100));
}

' Form.Load event (recommended)
Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs)
    '. . .
    lookUpEdit1.Properties.PopulateColumns()
    lookUpEdit1.Properties.Columns.Add(New DevExpress.XtraEditors.Controls.LookUpColumnInfo("Code", "Added in code", 100))
End Sub

' form constructor
Public Sub New()
    InitializeComponent()
    '. . .
    lookUpEdit1.Properties.ForceInitialize()
    lookUpEdit1.Properties.PopulateColumns()
    lookUpEdit1.Properties.Columns.Add(New DevExpress.XtraEditors.Controls.LookUpColumnInfo("Code", "Added in code", 100))
End Sub

using DevExpress.XtraEditors.Repository;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace LookupEdit_StandardBinding {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e) {
            InitData();

            gridControl1.DataSource = Products;
            gridView1.Columns["UnitPrice"].DisplayFormat.FormatType = DevExpress.Utils.FormatType.Numeric;
            gridView1.Columns["UnitPrice"].DisplayFormat.FormatString = "c2";

            // Create an in-place LookupEdit control.
            RepositoryItemLookUpEdit riLookup = new RepositoryItemLookUpEdit();
            riLookup.DataSource = Categories;
            riLookup.ValueMember = "ID";
            riLookup.DisplayMember = "CategoryName";

            // Enable the "best-fit" functionality mode in which columns have proportional widths and the popup window is resized to fit all the columns.
            riLookup.BestFitMode = DevExpress.XtraEditors.Controls.BestFitMode.BestFitResizePopup;
            // Specify the dropdown height.
            riLookup.DropDownRows = Categories.Count;

            // Enable the automatic completion feature. In this mode, when the dropdown is closed, 
            // the text in the edit box is automatically completed if it matches a DisplayMember field value of one of dropdown rows. 
            riLookup.SearchMode = DevExpress.XtraEditors.Controls.SearchMode.AutoComplete;
            // Specify the column against which an incremental search is performed in SearchMode.AutoComplete and SearchMode.OnlyInPopup modes
            riLookup.AutoSearchColumnIndex = 1;

            // Optionally hide the Description column in the dropdown.
            // riLookup.PopulateColumns();
            // riLookup.Columns["Description"].Visible = false;

            gridControl1.RepositoryItems.Add(riLookup);

            // Assign the in-place LookupEdit control to the grid's CategoryID column.
            // Note that the data types of the "ID" and "CategoryID" fields match.
            gridView1.Columns["CategoryID"].ColumnEdit = riLookup;
            gridView1.BestFitColumns();
        }

        List<Product> Products = new List<Product>();
        List<Category> Categories = new List<Category>();

        private void InitData() {
            Products.Add(new Product() { ProductName = "Sir Rodney's Scones", CategoryID = 3, UnitPrice = 10 });
            Products.Add(new Product() { ProductName = "Gustaf's Knäckebröd", CategoryID = 5, UnitPrice = 21 });
            Products.Add(new Product() { ProductName = "Tunnbröd", CategoryID = 5, UnitPrice = 9 });
            Products.Add(new Product() { ProductName = "Guaraná Fantástica", CategoryID = 1, UnitPrice = 4.5m });
            Products.Add(new Product() { ProductName = "NuNuCa Nuß-Nougat-Creme", CategoryID = 3, UnitPrice = 14 });
            Products.Add(new Product() { ProductName = "Gumbär Gummibärchen", CategoryID = 3, UnitPrice = 31.23m });
            Products.Add(new Product() { ProductName = "Rössle Sauerkraut", CategoryID = 7, UnitPrice = 45.6m });
            Products.Add(new Product() { ProductName = "Thüringer Rostbratwurst", CategoryID = 6, UnitPrice = 123.79m });
            Products.Add(new Product() { ProductName = "Nord-Ost Matjeshering", CategoryID = 8, UnitPrice = 25.89m });
            Products.Add(new Product() { ProductName = "Gorgonzola Telino", CategoryID = 4, UnitPrice = 12.5m });

            Categories.Add(new Category() { ID = 1, CategoryName = "Beverages", Description = "Soft drinks, coffees, teas, beers, and ales" });
            Categories.Add(new Category() { ID = 2, CategoryName = "Condiments", Description = "Sweet and savory sauces, relishes, spreads, and seasonings" });
            Categories.Add(new Category() { ID = 3, CategoryName = "Confections", Description = "Desserts, candies, and sweet breads" });
            Categories.Add(new Category() { ID = 4, CategoryName = "Dairy Products", Description = "Cheeses" });
            Categories.Add(new Category() { ID = 5, CategoryName = "Grains/Cereals", Description = "Breads, crackers, pasta, and cereal" });
            Categories.Add(new Category() { ID = 6, CategoryName = "Meat/Poultry", Description = "Prepared meats" });
            Categories.Add(new Category() { ID = 7, CategoryName = "Produce", Description = "Dried fruit and bean curd" });
            Categories.Add(new Category() { ID = 8, CategoryName = "Seafood", Description = "Seaweed and fish" });
        }
    }

    public class Product {
        public string ProductName { get; set; }
        public decimal UnitPrice { get; set; }
        public int CategoryID { get; set; }
    }

    public class Category {
        public int ID { get; set; }
        public string CategoryName { get; set; }
        public string Description { get; set; }
    }
}

Imports DevExpress.XtraEditors.Repository
Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Linq
Imports System.Text
Imports System.Threading.Tasks
Imports System.Windows.Forms

Namespace LookupEdit_StandardBinding
    Partial Public Class Form1
        Inherits Form

        Public Sub New()
            InitializeComponent()
        End Sub

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

            gridControl1.DataSource = Products
            gridView1.Columns("UnitPrice").DisplayFormat.FormatType = DevExpress.Utils.FormatType.Numeric
            gridView1.Columns("UnitPrice").DisplayFormat.FormatString = "c2"

            ' Create an in-place LookupEdit control.
            Dim riLookup As New RepositoryItemLookUpEdit()
            riLookup.DataSource = Categories
            riLookup.ValueMember = "ID"
            riLookup.DisplayMember = "CategoryName"

            ' Enable the "best-fit" functionality mode in which columns have proportional widths and the popup window is resized to fit all the columns.
            riLookup.BestFitMode = DevExpress.XtraEditors.Controls.BestFitMode.BestFitResizePopup
            ' Specify the dropdown height.
            riLookup.DropDownRows = Categories.Count

            ' Enable the automatic completion feature. In this mode, when the dropdown is closed, 
            ' the text in the edit box is automatically completed if it matches a DisplayMember field value of one of dropdown rows. 
            riLookup.SearchMode = DevExpress.XtraEditors.Controls.SearchMode.AutoComplete
            ' Specify the column against which an incremental search is performed in SearchMode.AutoComplete and SearchMode.OnlyInPopup modes
            riLookup.AutoSearchColumnIndex = 1

            ' Optionally hide the Description column in the dropdown.
            ' riLookup.PopulateColumns();
            ' riLookup.Columns["Description"].Visible = false;

            gridControl1.RepositoryItems.Add(riLookup)

            ' Assign the in-place LookupEdit control to the grid's CategoryID column.
            ' Note that the data types of the "ID" and "CategoryID" fields match.
            gridView1.Columns("CategoryID").ColumnEdit = riLookup
            gridView1.BestFitColumns()
        End Sub

        Private Products As New List(Of Product)()
        Private Categories As New List(Of Category)()

        Private Sub InitData()
            Products.Add(New Product() With {.ProductName = "Sir Rodney's Scones", .CategoryID = 3, .UnitPrice = 10})
            Products.Add(New Product() With {.ProductName = "Gustaf's Knäckebröd", .CategoryID = 5, .UnitPrice = 21})
            Products.Add(New Product() With {.ProductName = "Tunnbröd", .CategoryID = 5, .UnitPrice = 9})
            Products.Add(New Product() With {.ProductName = "Guaraná Fantástica", .CategoryID = 1, .UnitPrice = 4.5D})
            Products.Add(New Product() With {.ProductName = "NuNuCa Nuß-Nougat-Creme", .CategoryID = 3, .UnitPrice = 14})
            Products.Add(New Product() With {.ProductName = "Gumbär Gummibärchen", .CategoryID = 3, .UnitPrice = 31.23D})
            Products.Add(New Product() With {.ProductName = "Rössle Sauerkraut", .CategoryID = 7, .UnitPrice = 45.6D})
            Products.Add(New Product() With {.ProductName = "Thüringer Rostbratwurst", .CategoryID = 6, .UnitPrice = 123.79D})
            Products.Add(New Product() With {.ProductName = "Nord-Ost Matjeshering", .CategoryID = 8, .UnitPrice = 25.89D})
            Products.Add(New Product() With {.ProductName = "Gorgonzola Telino", .CategoryID = 4, .UnitPrice = 12.5D})

            Categories.Add(New Category() With {.ID = 1, .CategoryName = "Beverages", .Description = "Soft drinks, coffees, teas, beers, and ales"})
            Categories.Add(New Category() With {.ID = 2, .CategoryName = "Condiments", .Description = "Sweet and savory sauces, relishes, spreads, and seasonings"})
            Categories.Add(New Category() With {.ID = 3, .CategoryName = "Confections", .Description = "Desserts, candies, and sweet breads"})
            Categories.Add(New Category() With {.ID = 4, .CategoryName = "Dairy Products", .Description = "Cheeses"})
            Categories.Add(New Category() With {.ID = 5, .CategoryName = "Grains/Cereals", .Description = "Breads, crackers, pasta, and cereal"})
            Categories.Add(New Category() With {.ID = 6, .CategoryName = "Meat/Poultry", .Description = "Prepared meats"})
            Categories.Add(New Category() With {.ID = 7, .CategoryName = "Produce", .Description = "Dried fruit and bean curd"})
            Categories.Add(New Category() With {.ID = 8, .CategoryName = "Seafood", .Description = "Seaweed and fish"})
        End Sub
    End Class

    Public Class Product
        Public Property ProductName() As String
        Public Property UnitPrice() As Decimal
        Public Property CategoryID() As Integer
    End Class

    Public Class Category
        Public Property ID() As Integer
        Public Property CategoryName() As String
        Public Property Description() As String
    End Class
End Namespace

// and making one of them invisible
LookUpColumnInfoCollection coll = lookUpEditHints1.Properties.Columns;
coll.Add(new LookUpColumnInfo("Customer"));

' and making one of them invisible
Dim coll As LookUpColumnInfoCollection = lookUpEditHints1.Properties.Columns
coll.Add(New LookUpColumnInfo("Customer"))