Visual Basic Windows Forms Patterns

Modern Windows Forms development with VB.NET focusing on proper UI threading, data binding, and event handling.

Quick Start

' Form definition Public Class CustomerForm Inherits Form

Private customerService As ICustomerService
Private bindingSource As New BindingSource()

Public Sub New()
    InitializeComponent()
    customerService = New CustomerService()
End Sub

' Async load
Private Async Sub CustomerForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Await LoadCustomersAsync()
End Sub

Private Async Function LoadCustomersAsync() As Task
    Try
        Cursor = Cursors.WaitCursor
        Dim customers = Await customerService.GetAllAsync()
        bindingSource.DataSource = customers
        dataGridView.DataSource = bindingSource
    Catch ex As Exception
        MessageBox.Show($"Error loading customers: {ex.Message}", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
    Finally
        Cursor = Cursors.Default
    End Try
End Function

End Class

UI Threading Patterns

Invoke vs BeginInvoke

' Update UI from background thread Private Sub BackgroundWorker_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) ' Already on UI thread with BackgroundWorker progressBar.Value = e.ProgressPercentage lblStatus.Text = $"Processing: {e.ProgressPercentage}%" End Sub

' Manual invoke when needed Private Sub UpdateUIFromThread(text As String) If lblStatus.InvokeRequired Then lblStatus.Invoke(Sub() lblStatus.Text = text) Else lblStatus.Text = text End If End Sub

' Async pattern Private Async Sub btnProcess_Click(sender As Object, e As EventArgs) Handles btnProcess.Click btnProcess.Enabled = False Try Dim result = Await Task.Run(Function() LongRunningOperation()) lblResult.Text = result ' Safe - back on UI thread Finally btnProcess.Enabled = True End Try End Sub

BackgroundWorker Pattern

Private WithEvents bgWorker As New BackgroundWorker With { .WorkerReportsProgress = True, .WorkerSupportsCancellation = True }

Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click If Not bgWorker.IsBusy Then bgWorker.RunWorkerAsync() End If End Sub

Private Sub bgWorker_DoWork(sender As Object, e As DoWorkEventArgs) Handles bgWorker.DoWork For i = 0 To 100 If bgWorker.CancellationPending Then e.Cancel = True Exit For End If

    ' Simulate work
    Threading.Thread.Sleep(50)
    bgWorker.ReportProgress(i)
Next

End Sub

Private Sub bgWorker_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles bgWorker.ProgressChanged progressBar.Value = e.ProgressPercentage End Sub

Private Sub bgWorker_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles bgWorker.RunWorkerCompleted If e.Cancelled Then MessageBox.Show("Operation cancelled") ElseIf e.Error IsNot Nothing Then MessageBox.Show($"Error: {e.Error.Message}") Else MessageBox.Show("Operation completed") End If End Sub

Data Binding

BindingSource Pattern

Public Class CustomerForm Private bindingSource As New BindingSource() Private customers As List(Of Customer)

Private Async Sub Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    customers = Await customerService.GetAllAsync()

    ' Setup binding source
    bindingSource.DataSource = customers

    ' Bind controls
    dataGridView.DataSource = bindingSource
    txtName.DataBindings.Add("Text", bindingSource, "Name")
    txtEmail.DataBindings.Add("Text", bindingSource, "Email")

    ' Navigation
    bindingNavigator.BindingSource = bindingSource
End Sub

' Filter
Private Sub txtSearch_TextChanged(sender As Object, e As EventArgs) Handles txtSearch.TextChanged
    If String.IsNullOrEmpty(txtSearch.Text) Then
        bindingSource.RemoveFilter()
    Else
        bindingSource.Filter = $"Name LIKE '%{txtSearch.Text}%'"
    End If
End Sub

End Class

Object Data Binding

' Customer class with INotifyPropertyChanged Public Class Customer Implements INotifyPropertyChanged

Private _name As String
Public Property Name As String
    Get
        Return _name
    End Get
    Set(value As String)
        If _name <> value Then
            _name = value
            OnPropertyChanged(NameOf(Name))
        End If
    End Set
End Property

Public Event PropertyChanged As PropertyChangedEventHandler _
    Implements INotifyPropertyChanged.PropertyChanged

Protected Sub OnPropertyChanged(propertyName As String)
    RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
End Sub

End Class

Event Handling

Standard Event Pattern

' Button click Private Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click If ValidateForm() Then SaveCustomer() End If End Sub

' Multiple controls, same handler Private Sub TextBox_TextChanged(sender As Object, e As EventArgs) _ Handles txtName.TextChanged, txtEmail.TextChanged

ValidateForm()

End Sub

' Custom event arguments Public Class CustomerEventArgs Inherits EventArgs

Public Property Customer As Customer

Public Sub New(customer As Customer)
    Me.Customer = customer
End Sub

End Class

Public Event CustomerSaved As EventHandler(Of CustomerEventArgs)

Protected Sub OnCustomerSaved(customer As Customer) RaiseEvent CustomerSaved(Me, New CustomerEventArgs(customer)) End Sub

Form Validation

Private Function ValidateForm() As Boolean errorProvider.Clear() Dim isValid = True

' Validate name
If String.IsNullOrWhiteSpace(txtName.Text) Then
    errorProvider.SetError(txtName, "Name is required")
    isValid = False
End If

' Validate email
If String.IsNullOrWhiteSpace(txtEmail.Text) OrElse Not txtEmail.Text.Contains("@") Then
    errorProvider.SetError(txtEmail, "Valid email is required")
    isValid = False
End If

' Enable/disable save button
btnSave.Enabled = isValid

Return isValid

End Function

' Real-time validation Private Sub txtEmail_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) _ Handles txtEmail.Validating

If Not txtEmail.Text.Contains("@") Then
    errorProvider.SetError(txtEmail, "Invalid email format")
    e.Cancel = True
Else
    errorProvider.SetError(txtEmail, "")
End If

End Sub

Dialog Patterns

Custom Dialog Result

Public Class CustomerDialog Inherits Form

Public Property Customer As Customer

Private Sub btnOK_Click(sender As Object, e As EventArgs) Handles btnOK.Click
    If ValidateForm() Then
        Customer = New Customer With {
            .Name = txtName.Text,
            .Email = txtEmail.Text
        }
        DialogResult = DialogResult.OK
        Close()
    End If
End Sub

Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
    DialogResult = DialogResult.Cancel
    Close()
End Sub

End Class

' Usage Private Sub ShowCustomerDialog() Using dialog = New CustomerDialog() If dialog.ShowDialog() = DialogResult.OK Then ' Use dialog.Customer customers.Add(dialog.Customer) RefreshGrid() End If End Using End Sub

Best Practices

✅ DO

' Use async for I/O operations Private Async Sub btnLoad_Click(sender As Object, e As EventArgs) Handles btnLoad.Click Dim data = Await LoadDataAsync() End Sub

' Dispose resources properly Private Sub Form_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing connection?.Dispose() timer?.Dispose() End Sub

' Use BindingSource for data binding bindingSource.DataSource = customers dataGridView.DataSource = bindingSource

' Validate on events Private Sub txtName_Validating(sender As Object, e As CancelEventArgs) Handles txtName.Validating

' Use ErrorProvider for validation feedback errorProvider.SetError(txtName, "Name is required")

❌ DON'T

' Don't block UI thread Private Sub btnLoad_Click(sender As Object, e As EventArgs) Handles btnLoad.Click Dim data = LoadDataAsync().Result ' Blocks UI! End Sub

' Don't update UI from background thread directly Task.Run(Sub() lblStatus.Text = "Done" ' WRONG - cross-thread operation End Sub)

' Don't forget to dispose forms Dim form = New CustomerForm() form.Show() ' Memory leak - use Using or handle FormClosed

' Don't use Application.DoEvents While processing Application.DoEvents() ' Bad practice - use async instead End While

Related Skills

• vb-core: Core VB.NET patterns and type safety

• vb-database: Database integration with Windows Forms

• test-driven-development: Testing Windows Forms applications