Migrating VB6 Inventory Application to C# .NET 8 with WPF

Migration Plan

Phase 1: Assessment and Planning

1. Inventory existing functionality
   • Document all forms, modules, and classes
   • Identify database connections and data access methods
   • Map business logic and workflows
   • Identify third-party dependencies
2. Architecture planning
   • Design new solution structure using MVVM pattern
   • Plan database migration strategy
   • Define technology stack (EF Core, etc.)
   • Identify reusable components

Phase 2: Environment Setup

1. Development environment
   • Set up Visual Studio 2022
   • Create new WPF solution with .NET 8
   • Configure source control
   • Set up CI/CD pipeline
2. Create project structure
   • Create core projects (Models, ViewModels, Services)
   • Set up dependency injection
   • Configure logging and error handling

Phase 3: Database Migration

1. Database assessment
   • Analyze existing database schema
   • Plan migration to modern database if needed
   • Design Entity Framework Core models
2. Data access layer implementation
   • Create DbContext and entity configurations
   • Implement repositories
   • Create data migration scripts

Phase 4: UI Migration

1. UI design
   • Create WPF styles and themes
   • Design reusable controls
   • Implement base MVVM infrastructure
2. Form migration
   • Prioritize forms by complexity/importance
   • Implement one form at a time
   • Create unit tests for each form

Phase 5: Business Logic Migration

1. Service layer implementation
   • Migrate business logic to service classes
   • Implement validation rules
   • Create unit tests
2. Integration
   • Connect UI to services
   • Implement error handling
   • Add logging

Phase 6: Testing and Deployment

1. Testing
   • Unit testing
   • Integration testing
   • User acceptance testing
2. Deployment
   • Create installer
   • Document deployment process
   • Plan rollout strategy

Sample Migration: Inventory Item Form

Original VB6 Form (assumed)

1' frmInventoryItem.frm
2Option Explicit
3
4Private Sub Form_Load()
5    ' Initialize form
6    txtItemID.Text = ""
7    txtName.Text = ""
8    txtDescription.Text = ""
9    txtQuantity.Text = "0"
10    txtPrice.Text = "0.00"
11    cboCategory.Clear
12    
13    ' Load categories
14    Dim rs As ADODB.Recordset
15    Set rs = New ADODB.Recordset
16    rs.Open "SELECT CategoryID, CategoryName FROM Categories", conn, adOpenStatic
17    
18    Do Until rs.EOF
19        cboCategory.AddItem rs!CategoryName
20        cboCategory.ItemData(cboCategory.NewIndex) = rs!CategoryID
21        rs.MoveNext
22    Loop
23    rs.Close
24End Sub
25
26Private Sub btnSave_Click()
27    ' Validate input
28    If Trim(txtName.Text) = "" Then
29        MsgBox "Please enter item name", vbExclamation
30        txtName.SetFocus
31        Exit Sub
32    End If
33    
34    If Not IsNumeric(txtQuantity.Text) Then
35        MsgBox "Quantity must be numeric", vbExclamation
36        txtQuantity.SetFocus
37        Exit Sub
38    End If
39    
40    If Not IsNumeric(txtPrice.Text) Then
41        MsgBox "Price must be numeric", vbExclamation
42        txtPrice.SetFocus
43        Exit Sub
44    End If
45    
46    ' Save to database
47    Dim sql As String
48    If Trim(txtItemID.Text) = "" Then
49        ' Insert new record
50        sql = "INSERT INTO Inventory (Name, Description, CategoryID, Quantity, Price) VALUES ('" & _
51              Replace(txtName.Text, "'", "''") & "', '" & _
52              Replace(txtDescription.Text, "'", "''") & "', " & _
53              cboCategory.ItemData(cboCategory.ListIndex) & ", " & _
54              Val(txtQuantity.Text) & ", " & _
55              Val(txtPrice.Text) & ")"
56        conn.Execute sql
57        MsgBox "Item added successfully", vbInformation
58    Else
59        ' Update existing record
60        sql = "UPDATE Inventory SET Name = '" & Replace(txtName.Text, "'", "''") & _
61              "', Description = '" & Replace(txtDescription.Text, "'", "''") & _
62              "', CategoryID = " & cboCategory.ItemData(cboCategory.ListIndex) & _
63              ", Quantity = " & Val(txtQuantity.Text) & _
64              ", Price = " & Val(txtPrice.Text) & _
65              " WHERE ItemID = " & Val(txtItemID.Text)
66        conn.Execute sql
67        MsgBox "Item updated successfully", vbInformation
68    End If
69    
70    Unload Me
71End Sub
72
73Private Sub btnCancel_Click()
74    Unload Me
75End Sub

C# .NET 8 WPF Migration

1. Models

1// Models/InventoryItem.cs
2namespace InventoryApp.Models
3{
4    public class InventoryItem
5    {
6        public int ItemId { get; set; }
7        public string Name { get; set; } = string.Empty;
8        public string Description { get; set; } = string.Empty;
9        public int CategoryId { get; set; }
10        public string CategoryName { get; set; } = string.Empty;
11        public int Quantity { get; set; }
12        public decimal Price { get; set; }
13    }
14
15    public class Category
16    {
17        public int CategoryId { get; set; }
18        public string CategoryName { get; set; } = string.Empty;
19    }
20}

2. Data Access

1// Data/AppDbContext.cs
2using InventoryApp.Models;
3using Microsoft.EntityFrameworkCore;
4
5namespace InventoryApp.Data
6{
7    public class AppDbContext : DbContext
8    {
9        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }
10
11        public DbSet<InventoryItem> InventoryItems { get; set; }
12        public DbSet<Category> Categories { get; set; }
13
14        protected override void OnModelCreating(ModelBuilder modelBuilder)
15        {
16            modelBuilder.Entity<InventoryItem>().ToTable("Inventory");
17            modelBuilder.Entity<Category>().ToTable("Categories");
18        }
19    }
20}

3. Services

1// Services/IInventoryService.cs
2using InventoryApp.Models;
3using System.Collections.Generic;
4using System.Threading.Tasks;
5
6namespace InventoryApp.Services
7{
8    public interface IInventoryService
9    {
10        Task<List<Category>> GetCategoriesAsync();
11        Task<InventoryItem?> GetInventoryItemAsync(int id);
12        Task<bool> SaveInventoryItemAsync(InventoryItem item);
13    }
14}
15
16// Services/InventoryService.cs
17using InventoryApp.Data;
18using InventoryApp.Models;
19using Microsoft.EntityFrameworkCore;
20using System.Collections.Generic;
21using System.Threading.Tasks;
22
23namespace InventoryApp.Services
24{
25    public class InventoryService : IInventoryService
26    {
27        private readonly AppDbContext _dbContext;
28
29        public InventoryService(AppDbContext dbContext)
30        {
31            _dbContext = dbContext;
32        }
33
34        public async Task<List<Category>> GetCategoriesAsync()
35        {
36            return await _dbContext.Categories.ToListAsync();
37        }
38
39        public async Task<InventoryItem?> GetInventoryItemAsync(int id)
40        {
41            return await _dbContext.InventoryItems
42                .FirstOrDefaultAsync(i => i.ItemId == id);
43        }
44
45        public async Task<bool> SaveInventoryItemAsync(InventoryItem item)
46        {
47            try
48            {
49                if (item.ItemId == 0)
50                {
51                    await _dbContext.InventoryItems.AddAsync(item);
52                }
53                else
54                {
55                    _dbContext.InventoryItems.Update(item);
56                }
57                
58                await _dbContext.SaveChangesAsync();
59                return true;
60            }
61            catch
62            {
63                return false;
64            }
65        }
66    }
67}

4. ViewModel

1// ViewModels/InventoryItemViewModel.cs
2using CommunityToolkit.Mvvm.ComponentModel;
3using CommunityToolkit.Mvvm.Input;
4using InventoryApp.Models;
5using InventoryApp.Services;
6using System;
7using System.Collections.ObjectModel;
8using System.ComponentModel.DataAnnotations;
9using System.Threading.Tasks;
10using System.Windows;
11
12namespace InventoryApp.ViewModels
13{
14    public partial class InventoryItemViewModel : ObservableObject
15    {
16        private readonly IInventoryService _inventoryService;
17
18        [ObservableProperty]
19        private int _itemId;
20
21        [ObservableProperty]
22        [NotifyDataErrorInfo]
23        [Required(ErrorMessage = "Name is required")]
24        private string _name = string.Empty;
25
26        [ObservableProperty]
27        private string _description = string.Empty;
28
29        [ObservableProperty]
30        [NotifyDataErrorInfo]
31        [Range(0, int.MaxValue, ErrorMessage = "Quantity must be a positive number")]
32        private int _quantity;
33
34        [ObservableProperty]
35        [NotifyDataErrorInfo]
36        [Range(0, double.MaxValue, ErrorMessage = "Price must be a positive number")]
37        private decimal _price;
38
39        [ObservableProperty]
40        private Category? _selectedCategory;
41
42        [ObservableProperty]
43        private ObservableCollection<Category> _categories = new();
44
45        [ObservableProperty]
46        private bool _isLoading;
47
48        [ObservableProperty]
49        private string _windowTitle = "New Inventory Item";
50
51        public InventoryItemViewModel(IInventoryService inventoryService)
52        {
53            _inventoryService = inventoryService;
54        }
55
56        public async Task LoadDataAsync(int? itemId = null)
57        {
58            try
59            {
60                IsLoading = true;
61                
62                // Load categories
63                var categoryList = await _inventoryService.GetCategoriesAsync();
64                Categories = new ObservableCollection<Category>(categoryList);
65
66                // If editing existing item
67                if (itemId.HasValue && itemId.Value > 0)
68                {
69                    var item = await _inventoryService.GetInventoryItemAsync(itemId.Value);
70                    if (item != null)
71                    {
72                        ItemId = item.ItemId;
73                        Name = item.Name;
74                        Description = item.Description;
75                        Quantity = item.Quantity;
76                        Price = item.Price;
77                        SelectedCategory = Categories.FirstOrDefault(c => c.CategoryId == item.CategoryId);
78                        WindowTitle = "Edit Inventory Item";
79                    }
80                }
81            }
82            finally
83            {
84                IsLoading = false;
85            }
86        }
87
88        [RelayCommand]
89        private async Task SaveAsync()
90        {
91            if (SelectedCategory == null)
92            {
93                MessageBox.Show("Please select a category", "Validation Error", MessageBoxButton.OK, MessageBoxImage.Warning);
94                return;
95            }
96
97            var item = new InventoryItem
98            {
99                ItemId = ItemId,
100                Name = Name,
101                Description = Description,
102                CategoryId = SelectedCategory.CategoryId,
103                Quantity = Quantity,
104                Price = Price
105            };
106
107            var result = await _inventoryService.SaveInventoryItemAsync(item);
108            if (result)
109            {
110                MessageBox.Show(ItemId == 0 ? "Item added successfully" : "Item updated successfully", 
111                    "Success", MessageBoxButton.OK, MessageBoxImage.Information);
112                CloseWindow?.Invoke();
113            }
114            else
115            {
116                MessageBox.Show("Error saving item", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
117            }
118        }
119
120        [RelayCommand]
121        private void Cancel()
122        {
123            CloseWindow?.Invoke();
124        }
125
126        // Event to close the window
127        public Action? CloseWindow { get; set; }
128    }
129}

5. View

1<!-- Views/InventoryItemView.xaml -->
2<Window x:Class="InventoryApp.Views.InventoryItemView"
3        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
4        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
5        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
6        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
7        xmlns:vm="clr-namespace:InventoryApp.ViewModels"
8        mc:Ignorable="d"
9        Title="{Binding WindowTitle}"
10        Height="450" Width="500"
11        WindowStartupLocation="CenterOwner">
12    
13    <Window.Resources>
14        <Style TargetType="TextBlock">
15            <Setter Property="Margin" Value="0,5,0,2" />
16        </Style>
17        <Style TargetType="TextBox">
18            <Setter Property="Padding" Value="5" />
19            <Setter Property="Margin" Value="0,0,0,10" />
20        </Style>
21        <Style TargetType="ComboBox">
22            <Setter Property="Padding" Value="5" />
23            <Setter Property="Margin" Value="0,0,0,10" />
24        </Style>
25        <Style TargetType="Button">
26            <Setter Property="Padding" Value="15,5" />
27            <Setter Property="Margin" Value="5" />
28            <Setter Property="MinWidth" Value="80" />
29        </Style>
30    </Window.Resources>
31    
32    <Grid Margin="20">
33        <Grid.RowDefinitions>
34            <RowDefinition Height="*" />
35            <RowDefinition Height="Auto" />
36        </Grid.RowDefinitions>
37        
38        <StackPanel Grid.Row="0">
39            <TextBlock Text="Item Name:" />
40            <TextBox Text="{Binding Name, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
41            
42            <TextBlock Text="Description:" />
43            <TextBox Text="{Binding Description}" Height="60" TextWrapping="Wrap" AcceptsReturn="True" />
44            
45            <TextBlock Text="Category:" />
46            <ComboBox ItemsSource="{Binding Categories}" 
47                      SelectedItem="{Binding SelectedCategory}"
48                      DisplayMemberPath="CategoryName" />
49            
50            <TextBlock Text="Quantity:" />
51            <TextBox Text="{Binding Quantity, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
52            
53            <TextBlock Text="Price:" />
54            <TextBox Text="{Binding Price, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
55        </StackPanel>
56        
57        <StackPanel Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Right">
58            <Button Content="Save" Command="{Binding SaveCommand}" />
59            <Button Content="Cancel" Command="{Binding CancelCommand}" />
60        </StackPanel>
61        
62        <Grid Grid.RowSpan="2" Background="#80000000" Visibility="{Binding IsLoading, Converter={StaticResource BooleanToVisibilityConverter}}">
63            <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
64                <TextBlock Text="Loading..." Foreground="White" FontSize="16" HorizontalAlignment="Center" />
65                <ProgressBar IsIndeterminate="True" Width="200" Height="20" Margin="0,10,0,0" />
66            </StackPanel>
67        </Grid>
68    </Grid>
69</Window>

1// Views/InventoryItemView.xaml.cs
2using InventoryApp.ViewModels;
3using System.Windows;
4
5namespace InventoryApp.Views
6{
7    public partial class InventoryItemView : Window
8    {
9        private readonly InventoryItemViewModel _viewModel;
10
11        public InventoryItemView(InventoryItemViewModel viewModel, int? itemId = null)
12        {
13            InitializeComponent();
14            _viewModel = viewModel;
15            DataContext = _viewModel;
16            
17            _viewModel.CloseWindow = () => Close();
18            
19            Loaded += async (s, e) => 
20            {
21                await _viewModel.LoadDataAsync(itemId);
22            };
23        }
24    }
25}

6. App Startup and DI Configuration

1// App.xaml.cs
2using InventoryApp.Data;
3using InventoryApp.Services;
4using InventoryApp.ViewModels;
5using InventoryApp.Views;
6using Microsoft.EntityFrameworkCore;
7using Microsoft.Extensions.DependencyInjection;
8using Microsoft.Extensions.Hosting;
9using System.Windows;
10
11namespace InventoryApp
12{
13    public partial class App : Application
14    {
15        private readonly IHost _host;
16
17        public App()
18        {
19            _host = Host.CreateDefaultBuilder()
20                .ConfigureServices((context, services) =>
21                {
22                    // Register DbContext
23                    services.AddDbContext<AppDbContext>(options =>
24                        options.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=InventoryApp;Trusted_Connection=True;"));
25
26                    // Register services
27                    services.AddScoped<IInventoryService, InventoryService>();
28
29                    // Register ViewModels
30                    services.AddTransient<InventoryItemViewModel>();
31
32                    // Register Views
33                    services.AddTransient<InventoryItemView>();
34                    services.AddTransient<MainWindow>();
35                })
36                .Build();
37        }
38
39        protected override void OnStartup(StartupEventArgs e)
40        {
41            _host.Start();
42
43            var mainWindow = _host.Services.GetRequiredService<MainWindow>();
44            mainWindow.Show();
45
46            base.OnStartup(e);
47        }
48
49        protected override void OnExit(ExitEventArgs e)
50        {
51            _host.Dispose();
52            base.OnExit(e);
53        }
54    }
55}

Key Improvements in the Migration

1. Modern Architecture
   • MVVM pattern with clear separation of concerns
   • Dependency injection for better testability
   • Async/await for responsive UI
2. Data Access
   • Entity Framework Core instead of ADO.NET
   • Parameterized queries to prevent SQL injection
   • Repository pattern for data access
3. UI Improvements
   • WPF styling and templates
   • Data binding with validation
   • Loading indicators for async operations
4. Code Quality
   • Strong typing instead of variant types
   • Proper error handling
   • Input validation using data annotations
5. Maintainability
   • Organized project structure
   • Testable components
   • Modern C# language features

This migration approach provides a solid foundation for modernizing your VB6 inventory application while preserving its core functionality and improving it with modern development practices.