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 ClassUI 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 = $"Processing: {e.ProgressPercentage}%"
End Sub
' Manual invoke when needed
Private Sub UpdateUIFromThread(text As String)
If lblStatus.InvokeRequired Then
lblStatus.Invoke(Sub() lblStatus.Text = text)
Else
lblStatus.Text = text
End If
End Sub
' Async pattern
Private Async Sub btnProcess_Click(sender As Object, e As EventArgs) Handles btnProcess.Click
btnProcess.Enabled = False
Try
Dim result = Await Task.Run(Function() LongRunningOperation())
lblResult.Text = result ' Safe - back on UI thread
Finally
btnProcess.Enabled = True
End Try
End SubBackgroundWorker Pattern
Private WithEvents bgWorker As New BackgroundWorker With {
.WorkerReportsProgress = True,
.WorkerSupportsCancellation = True
}
Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
If Not bgWorker.IsBusy Then
bgWorker.RunWorkerAsync()
End If
End Sub
Private Sub bgWorker_DoWork(sender As Object, e As DoWorkEventArgs) Handles bgWorker.DoWork
For i = 0 To 100
If bgWorker.CancellationPending Then
e.Cancel = True
Exit For
End If
' Simulate work
Threading.Thread.Sleep(50)
bgWorker.ReportProgress(i)
Next
End Sub
Private Sub bgWorker_ProgressChanged(sender As Object, e As ProgressChangedEventArgs) Handles bgWorker.ProgressChanged
progressBar.Value = e.ProgressPercentage
End Sub
Private Sub bgWorker_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles bgWorker.RunWorkerCompleted
If e.Cancelled Then
MessageBox.Show("Operation cancelled")
ElseIf e.Error IsNot Nothing Then
MessageBox.Show($"Error: {e.Error.Message}")
Else
MessageBox.Show("Operation completed")
End If
End SubData 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 ClassObject 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 ClassEvent 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 SubForm 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 SubDialog 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 SubBest 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 WhileRelated Skills
- vb-core: Core VB.NET patterns and type safety
- vb-database: Database integration with Windows Forms
- test-driven-development: Testing Windows Forms applications