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