Windows Forms Applications

$ dotnet new winforms -lang VB -o ShelfDesktop
The template "Windows Forms App" was created successfully.

Processing post-creation actions...
Restoring ShelfDesktop.vbproj:
  Determining projects to restore...
/usr/share/dotnet/sdk/10.0.402/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.FrameworkReferenceResolution.targets(120,5): error NETSDK1100: To build a project targeting Windows on this operating system, set the EnableWindowsTargeting property to true.
Restore failed.
Post action failed.
Manual instructions: Run 'dotnet restore'


$ dotnet build
/usr/share/dotnet/sdk/10.0.402/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.FrameworkReferenceResolution.targets(120,5): error NETSDK1100: To build a project targeting Windows on this operating system, set the EnableWindowsTargeting property to true.
/usr/share/dotnet/sdk/10.0.402/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.FrameworkReferenceResolution.targets(120,5): error NETSDK1100: To build a project targeting Windows on this operating system, set the EnableWindowsTargeting property to true.
    0 Warning(s)
$ dotnet build -p:EnableWindowsTargeting=true
    0 Warning(s)
    0 Error(s)

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net10.0-windows</TargetFramework>
    <RootNamespace>ShelfDesktop</RootNamespace>
    <StartupObject>Sub Main</StartupObject>
    <UseWindowsForms>true</UseWindowsForms>
  </PropertyGroup>

  <ItemGroup>
    <Import Include="System.Data" />
    <Import Include="System.Drawing" />
    <Import Include="System.Windows.Forms" />
  </ItemGroup>

</Project>

Friend Module Program

    <STAThread()>
    Friend Sub Main(args As String())
        Application.SetHighDpiMode(HighDpiMode.SystemAware)
        Application.EnableVisualStyles()
        Application.SetCompatibleTextRenderingDefault(False)
        Application.Run(New Form1)
    End Sub

End Module

Public Class Form1

End Class

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()>
Partial Class Form1
    Inherits System.Windows.Forms.Form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()>
    Protected Overrides Sub Dispose(disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()>
    Private Sub InitializeComponent()
        components = New System.ComponentModel.Container()
        AutoScaleMode = AutoScaleMode.Font
        ClientSize = New Size(800, 450)
        Text = "Form1"
    End Sub

End Class

vbc : error BC30738: 'Sub Main' is declared more than once in 'ShelfDesktop': ShelfDesktop.My.MyApplication.Main(Args As String()), ShelfDesktop.Startup.Main()

Option Strict On

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()>
Partial Class AddBookForm
    Inherits System.Windows.Forms.Form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()>
    Protected Overrides Sub Dispose(disposing As Boolean)
        Try
            If disposing AndAlso components IsNot Nothing Then
                components.Dispose()
            End If
        Finally
            MyBase.Dispose(disposing)
        End Try
    End Sub

    Private components As System.ComponentModel.IContainer

    <System.Diagnostics.DebuggerStepThrough()>
    Private Sub InitializeComponent()
        components = New System.ComponentModel.Container()
        LayoutPanel = New System.Windows.Forms.TableLayoutPanel()
        TitleLabel = New System.Windows.Forms.Label()
        TitleTextBox = New System.Windows.Forms.TextBox()
        IsbnLabel = New System.Windows.Forms.Label()
        IsbnTextBox = New System.Windows.Forms.TextBox()
        YearLabel = New System.Windows.Forms.Label()
        YearUpDown = New System.Windows.Forms.NumericUpDown()
        Buttons = New System.Windows.Forms.FlowLayoutPanel()
        OkButton = New System.Windows.Forms.Button()
        DismissButton = New System.Windows.Forms.Button()
        Problems = New System.Windows.Forms.ErrorProvider(components)
        Tips = New System.Windows.Forms.ToolTip(components)
        LayoutPanel.SuspendLayout()
        CType(YearUpDown, System.ComponentModel.ISupportInitialize).BeginInit()
        Buttons.SuspendLayout()
        CType(Problems, System.ComponentModel.ISupportInitialize).BeginInit()
        SuspendLayout()
        '
        'LayoutPanel
        '
        LayoutPanel.ColumnCount = 2
        LayoutPanel.ColumnStyles.Add(New System.Windows.Forms.ColumnStyle())
        LayoutPanel.ColumnStyles.Add(New System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Percent, 100.0F))
        LayoutPanel.Controls.Add(TitleLabel, 0, 0)
        LayoutPanel.Controls.Add(TitleTextBox, 1, 0)
        LayoutPanel.Controls.Add(IsbnLabel, 0, 1)
        LayoutPanel.Controls.Add(IsbnTextBox, 1, 1)
        LayoutPanel.Controls.Add(YearLabel, 0, 2)
        LayoutPanel.Controls.Add(YearUpDown, 1, 2)
        LayoutPanel.Controls.Add(Buttons, 0, 3)
        LayoutPanel.SetColumnSpan(Buttons, 2)
        LayoutPanel.Dock = System.Windows.Forms.DockStyle.Fill
        LayoutPanel.Padding = New System.Windows.Forms.Padding(12)
        LayoutPanel.RowCount = 4
        LayoutPanel.RowStyles.Add(New System.Windows.Forms.RowStyle())
        LayoutPanel.RowStyles.Add(New System.Windows.Forms.RowStyle())
        LayoutPanel.RowStyles.Add(New System.Windows.Forms.RowStyle())
        LayoutPanel.RowStyles.Add(New System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 100.0F))
        '
        'TitleLabel
        '
        TitleLabel.Anchor = System.Windows.Forms.AnchorStyles.Left
        TitleLabel.AutoSize = True
        TitleLabel.Text = "&Title"
        '
        'TitleTextBox
        '
        TitleTextBox.Anchor = System.Windows.Forms.AnchorStyles.Left Or System.Windows.Forms.AnchorStyles.Right
        TitleTextBox.AccessibleName = "Title of the book"
        TitleTextBox.TabIndex = 0
        '
        'IsbnLabel
        '
        IsbnLabel.Anchor = System.Windows.Forms.AnchorStyles.Left
        IsbnLabel.AutoSize = True
        IsbnLabel.Text = "&ISBN-13"
        '
        'IsbnTextBox
        '
        IsbnTextBox.Anchor = System.Windows.Forms.AnchorStyles.Left Or System.Windows.Forms.AnchorStyles.Right
        IsbnTextBox.AccessibleName = "ISBN-13"
        IsbnTextBox.TabIndex = 1
        Tips.SetToolTip(IsbnTextBox, "Thirteen digits; hyphens are allowed")
        '
        'YearLabel
        '
        YearLabel.Anchor = System.Windows.Forms.AnchorStyles.Left
        YearLabel.AutoSize = True
        YearLabel.Text = "&Year"
        '
        'YearUpDown
        '
        YearUpDown.Anchor = System.Windows.Forms.AnchorStyles.Left
        YearUpDown.Maximum = New Decimal(New Integer() {2100, 0, 0, 0})
        YearUpDown.Minimum = New Decimal(New Integer() {1450, 0, 0, 0})
        YearUpDown.TabIndex = 2
        YearUpDown.Value = New Decimal(New Integer() {2000, 0, 0, 0})
        '
        'Buttons
        '
        Buttons.Anchor = System.Windows.Forms.AnchorStyles.Right
        Buttons.AutoSize = True
        Buttons.Controls.Add(OkButton)
        Buttons.Controls.Add(DismissButton)
        Buttons.FlowDirection = System.Windows.Forms.FlowDirection.RightToLeft
        '
        'OkButton
        '
        OkButton.Text = "&Add"
        OkButton.TabIndex = 3
        '
        'DismissButton
        '
        DismissButton.DialogResult = System.Windows.Forms.DialogResult.Cancel
        DismissButton.Text = "Cancel"
        DismissButton.CausesValidation = False
        DismissButton.TabIndex = 4
        '
        'Problems
        '
        Problems.ContainerControl = Me
        '
        'AddBookForm
        '
        AcceptButton = OkButton
        AutoScaleDimensions = New System.Drawing.SizeF(7.0F, 15.0F)
        AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        CancelButton = DismissButton
        ClientSize = New System.Drawing.Size(420, 190)
        Controls.Add(LayoutPanel)
        FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog
        MaximizeBox = False
        MinimizeBox = False
        Name = "AddBookForm"
        StartPosition = System.Windows.Forms.FormStartPosition.CenterParent
        Text = "Add a book"
        LayoutPanel.ResumeLayout(False)
        LayoutPanel.PerformLayout()
        CType(YearUpDown, System.ComponentModel.ISupportInitialize).EndInit()
        Buttons.ResumeLayout(False)
        CType(Problems, System.ComponentModel.ISupportInitialize).EndInit()
        ResumeLayout(False)
    End Sub

    Friend WithEvents LayoutPanel As System.Windows.Forms.TableLayoutPanel
    Friend WithEvents TitleLabel As System.Windows.Forms.Label
    Friend WithEvents TitleTextBox As System.Windows.Forms.TextBox
    Friend WithEvents IsbnLabel As System.Windows.Forms.Label
    Friend WithEvents IsbnTextBox As System.Windows.Forms.TextBox
    Friend WithEvents YearLabel As System.Windows.Forms.Label
    Friend WithEvents YearUpDown As System.Windows.Forms.NumericUpDown
    Friend WithEvents Buttons As System.Windows.Forms.FlowLayoutPanel
    Friend WithEvents OkButton As System.Windows.Forms.Button
    Friend WithEvents DismissButton As System.Windows.Forms.Button
    Friend WithEvents Problems As System.Windows.Forms.ErrorProvider
    Friend WithEvents Tips As System.Windows.Forms.ToolTip
End Class

e8.vb(6,24): warning BC40004: WithEvents variable 'Layout' conflicts with event 'Layout' in the base class 'Control' and should be declared 'Shadows'.
e8.vb(7,24): warning BC40004: WithEvents variable 'Resize' conflicts with event 'Resize' in the base class 'Control' and should be declared 'Shadows'.

Option Strict On

Imports System.ComponentModel

Public Class AddBookForm
    ' The result for the caller; Nothing until the user pressed Add with valid input.
    Public ReadOnly Property NewBook As Book

    Public Sub New()
        InitializeComponent()
        AutoValidate = AutoValidate.EnablePreventFocusChange
    End Sub

    Private Sub AddBookForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ActiveControl = TitleTextBox
    End Sub

    ' One handler for two events: the Handles clause takes a comma-separated list.
    Private Sub Fields_TextChanged(sender As Object, e As EventArgs) Handles TitleTextBox.TextChanged, IsbnTextBox.TextChanged
        OkButton.Enabled = TitleTextBox.TextLength > 0
    End Sub

    Private Sub TitleTextBox_Validating(sender As Object, e As CancelEventArgs) Handles TitleTextBox.Validating
        If String.IsNullOrWhiteSpace(TitleTextBox.Text) Then
            Problems.SetError(TitleTextBox, "A title is required.")
            e.Cancel = True
        End If
    End Sub

    Private Sub IsbnTextBox_Validating(sender As Object, e As CancelEventArgs) Handles IsbnTextBox.Validating
        If Not IsbnCheck.IsValid(IsbnTextBox.Text) Then
            Problems.SetError(IsbnTextBox, "Not a valid ISBN-13 (wrong length or check digit).")
            e.Cancel = True
        End If
    End Sub

    ' Validated is raised only after Validating finished without Cancel: clear the error here.
    Private Sub Fields_Validated(sender As Object, e As EventArgs) Handles TitleTextBox.Validated, IsbnTextBox.Validated
        Problems.SetError(DirectCast(sender, Control), "")
    End Sub

    Private Sub OkButton_Click(sender As Object, e As EventArgs) Handles OkButton.Click
        If Not ValidateChildren() Then Return
        _NewBook = New Book With {
            .Title = TitleTextBox.Text.Trim(),
            .Isbn = IsbnTextBox.Text,
            .Year = CInt(YearUpDown.Value)}
        DialogResult = DialogResult.OK
    End Sub
End Class

Option Strict On

Friend Module Startup
    <STAThread>
    Friend Sub Main()
        Application.SetHighDpiMode(HighDpiMode.PerMonitorV2)
        Application.EnableVisualStyles()
        Application.SetCompatibleTextRenderingDefault(False)
        Using dialog As New AddBookForm()
            If dialog.ShowDialog() = DialogResult.OK Then
                MessageBox.Show(dialog.NewBook.ToString(), "Added")
            End If
        End Using
    End Sub
End Module

Option Strict On

Public Class ListForm
    Inherits Form

    Private WithEvents AddButton As New Button()
    Private WithEvents YearBox As New NumericUpDown()
    Private WithEvents Choices As New ComboBox()

    Private Sub AddButton_Click(sender As Object, e As EventArgs) Handles AddButton.Click
        Dim year As Integer = YearBox.Value
        Dim choice As String = Choices.SelectedItem
        sender.Text = "Clicked"
    End Sub

    Private Async Function Later(sender As Object, e As EventArgs) As Task Handles AddButton.MouseEnter
        Await Task.Delay(1)
    End Function
End Class

Friend Module Startup
    <STAThread>
    Friend Sub Main()
    End Sub
End Module

e6.vb(11,31): error BC30512: Option Strict On disallows implicit conversions from 'Decimal' to 'Integer'.
e6.vb(12,32): error BC30512: Option Strict On disallows implicit conversions from 'Object' to 'String'.
e6.vb(13,9): error BC30574: Option Strict On disallows late binding.
e6.vb(16,84): warning BC42359: The Task returned from this Async Function will be dropped, and any exceptions in it ignored. Consider changing it to an Async Sub so its exceptions are propagated.

e2.vb(8,75): error BC30506: Handles clause requires a WithEvents variable defined in the containing type or one of its base types.
e3.vb(8,85): error BC30590: Event 'Clck' cannot be found.
e4.vb(8,82): error BC31029: Method 'AddButton_Click' cannot handle event 'Click' because they do not have a compatible signature.

Option Strict On

Imports System.ComponentModel
Imports System.IO
Imports System.Threading

' A form written entirely in code: no designer file, controls created and wired by hand.
Public Class CatalogForm
    Inherits Form

    Private ReadOnly _books As New BindingList(Of Book)()
    Private ReadOnly _source As New BindingSource()
    Private ReadOnly _grid As New DataGridView()
    Private ReadOnly _status As New StatusStrip()
    Private ReadOnly _statusLabel As New ToolStripStatusLabel("Ready")
    Private ReadOnly _progress As New ToolStripProgressBar() With {.Visible = False}
    Private ReadOnly _titleBox As New TextBox() With {.Dock = DockStyle.Top}
    Private _loading As CancellationTokenSource

    Public Sub New()
        Text = "Shelf catalogue"
        ClientSize = New Size(640, 360)

        ' Menu
        Dim menu As New MenuStrip()
        Dim fileMenu As New ToolStripMenuItem("&File")
        Dim openItem As New ToolStripMenuItem("&Open CSV...", Nothing, AddressOf OpenItem_Click) With {
            .ShortcutKeys = Keys.Control Or Keys.O}
        Dim addItem As New ToolStripMenuItem("&Add book...", Nothing, AddressOf AddItem_Click)
        Dim exitItem As New ToolStripMenuItem("E&xit", Nothing, Sub(s, e) Close())
        fileMenu.DropDownItems.AddRange({openItem, addItem, New ToolStripSeparator(), exitItem})
        menu.Items.Add(fileMenu)
        MainMenuStrip = menu

        ' Status bar
        _status.Items.AddRange({_statusLabel, _progress})

        ' Grid bound through a BindingSource to a BindingList(Of Book)
        _source.DataSource = _books
        _grid.Dock = DockStyle.Fill
        _grid.AutoGenerateColumns = False
        _grid.AllowUserToAddRows = False
        _grid.SelectionMode = DataGridViewSelectionMode.FullRowSelect
        _grid.Columns.Add(New DataGridViewTextBoxColumn() With {.DataPropertyName = "Title", .HeaderText = "Title", .AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill})
        _grid.Columns.Add(New DataGridViewTextBoxColumn() With {.DataPropertyName = "Year", .HeaderText = "Year", .Width = 70})
        _grid.Columns.Add(New DataGridViewTextBoxColumn() With {.DataPropertyName = "Isbn", .HeaderText = "ISBN", .Width = 140})
        _grid.DataSource = _source

        ' A simple-bound TextBox: editing the text edits the current book
        _titleBox.DataBindings.Add("Text", _source, "Title", True, DataSourceUpdateMode.OnPropertyChanged)

        Controls.Add(_grid)
        Controls.Add(_titleBox)
        Controls.Add(menu)
        Controls.Add(_status)
        AddHandler _books.ListChanged, AddressOf Books_ListChanged
    End Sub

    Private Sub Books_ListChanged(sender As Object, e As ListChangedEventArgs)
        _statusLabel.Text = _books.Count.ToString() & " book(s)"
    End Sub

    Private Sub AddItem_Click(sender As Object, e As EventArgs)
        Using dialog As New AddBookForm()
            If dialog.ShowDialog(Me) = DialogResult.OK Then _books.Add(dialog.NewBook)
        End Using
    End Sub

    ' An Async Sub is correct here: an event handler must be a Sub. Catch everything inside it.
    Private Async Sub OpenItem_Click(sender As Object, e As EventArgs)
        Using dialog As New OpenFileDialog() With {.Filter = "CSV files (*.csv)|*.csv|All files (*.*)|*.*"}
            If dialog.ShowDialog(Me) <> DialogResult.OK Then Return
            _loading?.Cancel()
            _loading = New CancellationTokenSource()
            Dim token = _loading.Token
            Dim progress As New Progress(Of Integer)(
                Sub(percent)
                    _progress.Value = percent        ' runs on the UI thread: Progress captured its context
                End Sub)
            _progress.Visible = True
            Try
                Dim rows = Await Task.Run(Function() ReadBooks(dialog.FileName, progress, token), token)
                For Each book In rows
                    _books.Add(book)
                Next
                _statusLabel.Text = "Loaded " & rows.Count.ToString() & " book(s)"
            Catch ex As OperationCanceledException
                _statusLabel.Text = "Cancelled"
            Catch ex As IOException
                Dim page As New TaskDialogPage() With {
                    .Caption = "Shelf",
                    .Heading = "The file could not be read",
                    .Text = ex.Message,
                    .Icon = TaskDialogIcon.Error}
                page.Buttons.Add(TaskDialogButton.OK)
                TaskDialog.ShowDialog(Me, page)
            Finally
                _progress.Visible = False
            End Try
        End Using
    End Sub

    ' Runs on a thread-pool thread: it must not touch any control.
    Private Shared Function ReadBooks(path As String, progress As IProgress(Of Integer), token As CancellationToken) As List(Of Book)
        Dim lines = File.ReadAllLines(path)
        Dim result As New List(Of Book)
        For i = 1 To lines.Length - 1
            token.ThrowIfCancellationRequested()
            Dim f = lines(i).Split(","c)
            If f.Length >= 3 Then
                result.Add(New Book With {.Title = f(0), .Year = Integer.Parse(f(1)), .Isbn = f(2)})
            End If
            progress.Report(CInt(i * 100 \ lines.Length))
        Next
        Return result
    End Function

    Protected Overrides Sub OnFormClosing(e As FormClosingEventArgs)
        If _books.Count > 0 Then
            Dim answer = MessageBox.Show(Me, "Close the catalogue?", "Shelf", MessageBoxButtons.YesNo, MessageBoxIcon.Question)
            If answer = DialogResult.No Then e.Cancel = True
        End If
        MyBase.OnFormClosing(e)
    End Sub
End Class

Option Strict On

Imports System.ComponentModel
Imports System.Runtime.CompilerServices

' A trimmed copy of the Shelf.Core Book: it raises PropertyChanged, so bound controls update.
Public Class Book
    Implements INotifyPropertyChanged

    Private _title As String = ""
    Private _year As Integer
    Private _isbn As String = ""

    Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

    Public Property Title As String
        Get
            Return _title
        End Get
        Set(value As String)
            SetField(_title, value)
        End Set
    End Property

    Public Property Year As Integer
        Get
            Return _year
        End Get
        Set(value As Integer)
            SetField(_year, value)
        End Set
    End Property

    Public Property Isbn As String
        Get
            Return _isbn
        End Get
        Set(value As String)
            SetField(_isbn, value)
        End Set
    End Property

    Private Sub SetField(Of T)(ByRef field As T, value As T, <CallerMemberName> Optional name As String = Nothing)
        If EqualityComparer(Of T).Default.Equals(field, value) Then Return
        field = value
        RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
    End Sub

    Public Overrides Function ToString() As String
        Return $"{Title} ({Year})"
    End Function
End Class

Public Module IsbnCheck
    ' ISBN-13 check digit, as in Shelf.Core.Isbn.
    Public Function IsValid(text As String) As Boolean
        Dim digits = New String(If(text, "").Where(AddressOf Char.IsDigit).ToArray())
        If digits.Length <> 13 Then Return False
        Dim sum = 0
        For i = 0 To 12
            Dim d = AscW(digits(i)) - AscW("0"c)
            sum += If(i Mod 2 = 0, d, d * 3)
        Next
        Return sum Mod 10 = 0
    End Function
End Module

Option Strict On

Imports System.Threading

Public Class CrossThreadForm
    Inherits Form

    Private ReadOnly _label As New Label() With {.Dock = DockStyle.Fill, .TextAlign = ContentAlignment.MiddleCenter}
    Private ReadOnly _panel As New FlowLayoutPanel() With {.Dock = DockStyle.Bottom, .AutoSize = True}
    Private ReadOnly _wrong As New Button() With {.Text = "Wrong", .AutoSize = True}
    Private ReadOnly _invoke As New Button() With {.Text = "Invoke", .AutoSize = True}
    Private ReadOnly _async As New Button() With {.Text = "Await", .AutoSize = True}

    Public Sub New()
        _panel.Controls.AddRange({_wrong, _invoke, _async})
        Controls.Add(_label)
        Controls.Add(_panel)
        AddHandler _wrong.Click, AddressOf Wrong_Click
        AddHandler _invoke.Click, AddressOf Invoke_Click
        AddHandler _async.Click, AddressOf Async_Click
    End Sub

    ' Wrong: a worker thread touches a control. At run time WinForms throws InvalidOperationException
    ' ("Cross-thread operation not valid") on the worker thread, and the process ends if nothing catches it.
    Private Sub Wrong_Click(sender As Object, e As EventArgs)
        Dim worker As New Thread(Sub() _label.Text = "from a worker thread")
        worker.Start()
    End Sub

    ' Right, explicit: marshal the call to the UI thread. InvokeRequired is False on the UI thread itself.
    Private Sub Invoke_Click(sender As Object, e As EventArgs)
        Dim worker As New Thread(
            Sub()
                Dim text = "computed on thread " & Environment.CurrentManagedThreadId.ToString()
                If _label.InvokeRequired Then
                    _label.Invoke(Sub() _label.Text = text)
                Else
                    _label.Text = text
                End If
            End Sub)
        worker.Start()
    End Sub

    ' Right, usual today: Await resumes on the UI thread because the click handler started there.
    Private Async Sub Async_Click(sender As Object, e As EventArgs)
        _async.Enabled = False
        Try
            Dim text = Await Task.Run(Function() "computed on thread " & Environment.CurrentManagedThreadId.ToString())
            _label.Text = text
        Finally
            _async.Enabled = True
        End Try
    End Sub

    ' .NET 9 and later: Control.InvokeAsync hops to the UI thread from any thread and returns a Task.
    Public Function ShowFromAnyThreadAsync(text As String) As Task
        Return _label.InvokeAsync(Sub() _label.Text = text)
    End Function
End Class

internal sealed class MyForms   // nested in the hidden module My.MyProject
{
	[ThreadStatic]
	private static Hashtable m_FormBeingCreated;

	public MainForm m_MainForm;

	public MainForm MainForm
	{
		get
		{
			m_MainForm = Create__Instance__(m_MainForm);
			return m_MainForm;
		}
		set
		{
			if (value != m_MainForm)
			{
				if (value != null)
				{
					throw new ArgumentException("Property can only be set to Nothing");
				}
				Dispose__Instance__(ref m_MainForm);
			}
		}
	}

	// the same property exists for every other Form class of the project (AddBookForm, SplashForm)

	private static T Create__Instance__<T>(T Instance) where T : Form, new()
	{
		if (Instance == null || ((Control)Instance).IsDisposed)
		{
			if (m_FormBeingCreated != null)
			{
				if (m_FormBeingCreated.ContainsKey(typeof(T)))
				{
					throw new InvalidOperationException(Utils.GetResourceString("WinForms_RecursiveFormCreate"));
				}
			}
			else
			{
				m_FormBeingCreated = new Hashtable();
			}
			m_FormBeingCreated.Add(typeof(T), null);
			try
			{
				return new T();
			}
			// catch (TargetInvocationException): rethrown as InvalidOperationException with the inner message
			finally
			{
				m_FormBeingCreated.Remove(typeof(T));
			}
		}
		return Instance;
	}

	private void Dispose__Instance__<T>(ref T instance) where T : Form
	{
		((Component)instance/*cast due to constrained. prefix*/).Dispose();
		instance = default;
	}
}

Option Strict On

Public Class Form1
    Inherits Form
End Class

Friend Module Startup
    <STAThread>
    Friend Sub Main()
        Form1.Show()
    End Sub
End Module

e1.vb(10,9): error BC30469: Reference to a non-shared member requires an object reference.

Option Strict On

Imports System.ComponentModel
Imports System.Drawing.Drawing2D

' A custom control: draws itself, raises an event, takes keyboard and mouse input.
<DefaultEvent("RatingChanged")>
Public Class RatingControl
    Inherits Control

    Private _rating As Integer
    Private _maximum As Integer = 5

    <Category("Behavior"), Description("The current rating."), DefaultValue(0)>
    Public Property Rating As Integer
        Get
            Return _rating
        End Get
        Set(value As Integer)
            value = Math.Clamp(value, 0, _maximum)
            If value = _rating Then Return
            _rating = value
            Invalidate()
            OnRatingChanged(EventArgs.Empty)
        End Set
    End Property

    <Category("Behavior"), Description("How many stars are shown."), DefaultValue(5)>
    Public Property Maximum As Integer
        Get
            Return _maximum
        End Get
        Set(value As Integer)
            _maximum = Math.Max(1, value)
            Rating = Math.Min(_rating, _maximum)
            Invalidate()
        End Set
    End Property

    <Category("Property Changed"), Description("Raised when Rating changes.")>
    Public Event RatingChanged As EventHandler

    Protected Overridable Sub OnRatingChanged(e As EventArgs)
        RaiseEvent RatingChanged(Me, e)
    End Sub

    Public Sub New()
        DoubleBuffered = True
        SetStyle(ControlStyles.Selectable Or ControlStyles.UserPaint Or ControlStyles.ResizeRedraw, True)
        TabStop = True
        AccessibleRole = AccessibleRole.Slider
        Size = New Size(130, 28)
    End Sub

    Protected Overrides Sub OnPaint(e As PaintEventArgs)
        MyBase.OnPaint(e)
        e.Graphics.SmoothingMode = SmoothingMode.AntiAlias
        Dim cell = ClientSize.Width / _maximum
        For i = 0 To _maximum - 1
            Dim box As New RectangleF(CSng(i * cell) + 2, 2, CSng(cell) - 4, ClientSize.Height - 4)
            Using brush As New SolidBrush(If(i < _rating, Color.Goldenrod, Color.LightGray))
                e.Graphics.FillEllipse(brush, box)
            End Using
        Next
        If Focused AndAlso ShowFocusCues Then
            ControlPaint.DrawFocusRectangle(e.Graphics, ClientRectangle)
        End If
    End Sub

    Protected Overrides Sub OnMouseDown(e As MouseEventArgs)
        MyBase.OnMouseDown(e)
        Focus()
        Rating = CInt(Math.Ceiling(e.X / (ClientSize.Width / _maximum)))
    End Sub

    Protected Overrides Function IsInputKey(keyData As Keys) As Boolean
        Return keyData = Keys.Left OrElse keyData = Keys.Right OrElse MyBase.IsInputKey(keyData)
    End Function

    Protected Overrides Sub OnKeyDown(e As KeyEventArgs)
        MyBase.OnKeyDown(e)
        If e.KeyCode = Keys.Right Then Rating += 1
        If e.KeyCode = Keys.Left Then Rating -= 1
    End Sub

    Protected Overrides Sub OnGotFocus(e As EventArgs)
        MyBase.OnGotFocus(e)
        Invalidate()
    End Sub

    Protected Overrides Sub OnLostFocus(e As EventArgs)
        MyBase.OnLostFocus(e)
        Invalidate()
    End Sub
End Class

' A UserControl: several existing controls composed into one reusable unit.
Public Class IsbnBox
    Inherits UserControl

    Private ReadOnly _text As New TextBox() With {.Dock = DockStyle.Fill}
    Private ReadOnly _mark As New Label() With {.Dock = DockStyle.Right, .Width = 24, .TextAlign = ContentAlignment.MiddleCenter}

    Public Event IsValidChanged As EventHandler

    Public Sub New()
        Controls.Add(_text)
        Controls.Add(_mark)
        Height = _text.PreferredHeight
        AddHandler _text.TextChanged, AddressOf Text_TextChanged
    End Sub

    <Browsable(True), DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)>
    Public Overrides Property Text As String
        Get
            Return _text.Text
        End Get
        Set(value As String)
            _text.Text = value
        End Set
    End Property

    <Browsable(False)>
    Public ReadOnly Property IsValid As Boolean
        Get
            Return IsbnCheck.IsValid(_text.Text)
        End Get
    End Property

    Private Sub Text_TextChanged(sender As Object, e As EventArgs)
        _mark.Text = If(IsValid, ChrW(&H2713), "")
        RaiseEvent IsValidChanged(Me, EventArgs.Empty)
    End Sub
End Class

Option Strict On

Imports Microsoft.Extensions.DependencyInjection
Imports Microsoft.Extensions.Hosting
Imports Microsoft.VisualBasic.ApplicationServices

' The Generic Host inside the Application Framework: build it in Startup, stop it in Shutdown,
' and resolve the main form from the container instead of using the default form instance.
Namespace My
    Partial Friend Class MyApplication
        Private Shared _host As IHost

        Friend Shared ReadOnly Property Services As IServiceProvider
            Get
                Return _host.Services
            End Get
        End Property

        Private Sub MyApplication_Startup(sender As Object, e As StartupEventArgs) Handles Me.Startup
            Dim builder = Host.CreateApplicationBuilder(e.CommandLine.ToArray())
            builder.Services.AddSingleton(Of ICatalogService, CatalogService)()
            builder.Services.AddTransient(Of MainForm)()
            _host = builder.Build()
            _host.Start()
        End Sub

        Private Sub MyApplication_Shutdown(sender As Object, e As EventArgs) Handles Me.Shutdown
            _host.StopAsync().GetAwaiter().GetResult()
            _host.Dispose()
        End Sub

        Protected Overrides Sub OnCreateMainForm()
            MainForm = Services.GetRequiredService(Of MainForm)()
        End Sub
    End Class
End Namespace

Option Strict On

Imports Microsoft.Extensions.Logging

Public Class MainForm
    Inherits Form

    Private ReadOnly _logger As ILogger(Of MainForm)
    Private ReadOnly _catalog As ICatalogService

    ' Constructor injection into a form: the designer needs a parameterless constructor too
    ' (it is used only at design time), but the container uses this one.
    Public Sub New(catalog As ICatalogService, logger As ILogger(Of MainForm))
        _catalog = catalog
        _logger = logger
        Text = "Shelf (" & _catalog.Count().ToString() & " books)"
        _logger.LogInformation("Main form created")
    End Sub

    Public Sub New()
        InitializeDesignTime()
    End Sub

    Private Sub InitializeDesignTime()
        Text = "Shelf (design time)"
    End Sub
End Class

Option Strict On

Public Interface ICatalogService
    Function Count() As Integer
End Interface

Public Class CatalogService
    Implements ICatalogService

    Public Function Count() As Integer Implements ICatalogService.Count
        Return 3
    End Function
End Class

Option Strict On

Imports Microsoft.Extensions.DependencyInjection
Imports Microsoft.Extensions.Hosting

' The Generic Host in a WinForms program: forms and services come from the container.
Friend Module HostStartup
    <STAThread>
    Friend Sub Main(args As String())
        Dim builder = Host.CreateApplicationBuilder(args)
        builder.Services.AddTransient(Of CatalogForm)()
        builder.Services.AddTransient(Of AddBookForm)()

        Using host = builder.Build()
            Application.SetHighDpiMode(HighDpiMode.PerMonitorV2)
            Application.EnableVisualStyles()
            Application.SetCompatibleTextRenderingDefault(False)
            host.Start()
            Try
                Application.Run(host.Services.GetRequiredService(Of CatalogForm)())
            Finally
                host.StopAsync().GetAwaiter().GetResult()
            End Try
        End Using
    End Sub
End Module

<?xml version="1.0" encoding="utf-8"?>
<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
  <assemblyIdentity version="1.0.0.0" name="ShelfDesktop.app"/>
  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
    <application>
      <!-- Windows 10 and Windows 11 -->
      <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}"/>
    </application>
  </compatibility>
  <application xmlns="urn:schemas-microsoft-com:asm.v3">
    <windowsSettings>
      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
    </windowsSettings>
  </application>
</assembly>

<?xml version="1.0" encoding="utf-8"?>
<root>
  <resheader name="resmimetype"><value>text/microsoft-resx</value></resheader>
  <resheader name="version"><value>2.0</value></resheader>
  <resheader name="reader"><value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value></resheader>
  <resheader name="writer"><value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value></resheader>
  <data name="AddBookTitle" xml:space="preserve"><value>Add a book</value></data>
  <data name="OkButton" xml:space="preserve"><value>&amp;Add</value></data>
  <data name="BookCount" xml:space="preserve"><value>{0} book(s) in the catalogue</value></data>
</root>

Option Strict On

Imports System.Globalization
Imports System.Reflection
Imports System.Resources

' The lookup WinForms uses for a Localizable form, done by hand: one .resx per culture,
' satellite assemblies built by MSBuild, and a fallback chain from specific to neutral.
Module Program
    Sub Main()
        Dim manager As New ResourceManager("ShelfApp.Strings", Assembly.GetExecutingAssembly())
        For Each name In {"en", "de", "es", "de-AT", "fr"}
            Dim culture = CultureInfo.GetCultureInfo(name)
            Console.WriteLine($"{name,-6} {manager.GetString("AddBookTitle", culture),-18} {manager.GetString("OkButton", culture),-12} " &
                              String.Format(culture, manager.GetString("BookCount", culture), 1234.5))
        Next

        ' The UI culture picks the language of resources; the culture (CurrentCulture) formats numbers and dates.
        CultureInfo.CurrentUICulture = CultureInfo.GetCultureInfo("de")
        CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("de")
        Console.WriteLine(manager.GetString("AddBookTitle") & " / " & (1234.5).ToString("N1"))
        Console.WriteLine("Satellite assembly folders: " &
            String.Join(", ", IO.Directory.GetDirectories(AppContext.BaseDirectory).Select(AddressOf IO.Path.GetFileName).OrderBy(Function(n) n)))
    End Sub
End Module

en     Add a book         &Add         1234.5 book(s) in the catalogue
de     Buch hinzufügen    &Hinzufügen  1234,5 Buch/Bücher im Katalog
es     Añadir un libro    &Añadir      1234,5 libro(s) en el catálogo
de-AT  Buch hinzufügen    &Hinzufügen  1234,5 Buch/Bücher im Katalog
fr     Add a book         &Add         1234,5 book(s) in the catalogue
Buch hinzufügen / 1.234,5
Satellite assembly folders: de, es