Form with Input Window, where a mechanism shall check if data has been entered

Question

I need it to not close when user press enter or exit so that it mandate for user to make entry for all three box. I am new to powershell so I might be sounding akward but I can't find a good solution anywhere.   1st Textbox for username 2nd Dropbox for Country 3rd Dropbox for City

Also want heading of each box

function GenerateForm {

#region Import the Assemblies
[reflection.assembly]::loadwithpartialname("System.Windows.Forms") | Out-Null
[reflection.assembly]::loadwithpartialname("System.Drawing") | Out-Null
#endregion

#region Generated Form Objects
$form1 = New-Object System.Windows.Forms.Form
$button1 = New-Object System.Windows.Forms.Button
$button2 = New-Object System.Windows.Forms.Button
$textBox2 = New-Object System.Windows.Forms.TextBox
$textBox1 = New-Object System.Windows.Forms.TextBox
$comboBox1 = New-Object System.Windows.Forms.ComboBox
$InitialFormWindowState = New-Object System.Windows.Forms.FormWindowState
#endregion Generated Form Objects

    #region $handler_comboBox1_SelectedIndexChanged
$handler_comboBox1_SelectedIndexChanged=
{
#TODO: Place custom script here
    try{
    if ($comboBox1.Text.Length -gt 0)
    {
        $form1.Text = $comboBox1.Text;
    }
    }catch{} #in case no items are available
}
    #endregion $handler_comboBox1_SelectedIndexChanged
    #region $handler_button1_Click
$handler_button1_Click=
{
#TODO: Place custom script here
    try{
    #How to add one item
    #$textBox1.Text
    if ($textBox1.Text.Length -gt 0 -and `
        $textBox2.Text.Length -eq 0)
    {
        $comboBox1.Items.Add($textBox1.Text);
        Write-Host "Added " $textBox1.Text "from `$textBox1";
    }
    #$textBox2.Text
    elseif ($textBox1.Text.Length -eq 0 -and `
        $textBox2.Text.Length -gt 0)
    {
        $comboBox1.Items.Add($textBox2.Text);
        Write-Host "Added " $textBox2.Text "from `$textBox2";
    }
    #$textBox1.Text and $textBox2.Text
    elseif ($textBox1.Text.Length -gt 0 -and `
        $textBox2.Text.Length -gt 0)
    {
        $comboBox1.Items.AddRange(($textBox1.Text, $textBox2.Text));
        Write-Host "Added " $textBox1.Text "from `$textBox1";
        Write-Host "Added " $textBox2.Text "from `$textBox2";
    }
    else
    {
        #Nothing to add
        #$textBox1.Text.Length -eq 0
        #$textBox2.Text.Length -eq 0
    }
    #At last, if the user typed something
    if ($comboBox1.Text.Length -gt 0)
    {
        $comboBox1.Items.Add($comboBox1.Text);
        Write-Host "Added " $comboBox1.Text "from `$comboBox1";
    }
    }catch{} #for example, no data in the both textboxes
}
    #endregion $handler_button1_Click
    #region $handler_button2_Click
$handler_button2_Click=
{
#TODO: Place custom script here
    try{
    #Clean up the combo box
    $comboBox1.Items.Clear();
    $comboBox1.Text = "";
    }catch{}
}
    #endregion $handler_button2_Click
$OnLoadForm_StateCorrection=
{#Correct the initial state of the form to prevent the .Net maximized form issue
    $form1.WindowState = $InitialFormWindowState
}

#----------------------------------------------
#region Generated Form Code
    #region $form1
$form1.Text = "Input Form"
$form1.Name = "form1"
$form1.DataBindings.DefaultDataSourceUpdateMode = 0
$System_Drawing_Size = New-Object System.Drawing.Size
$System_Drawing_Size.Width = 282
$System_Drawing_Size.Height = 220
$form1.ClientSize = $System_Drawing_Size
    #endregion $form1
    #region $button1
$button1.TabIndex = 3
$button1.Name = "Enter"
$System_Drawing_Size = New-Object System.Drawing.Size
$System_Drawing_Size.Width = 70
$System_Drawing_Size.Height = 30
$button1.Size = $System_Drawing_Size
$button1.UseVisualStyleBackColor = $True
$button1.Text = "Enter"
$System_Drawing_Point = New-Object System.Drawing.Point
$System_Drawing_Point.X = 195
$System_Drawing_Point.Y = 160
$button1.Location = $System_Drawing_Point
$button1.DataBindings.DefaultDataSourceUpdateMode = 0
$button1.add_Click($handler_button1_Click)
$form1.Controls.Add($button1)
    #endregion $button1
    #region $button2
$button2.TabIndex = 4
$button2.Name = "Exit"
$System_Drawing_Size = New-Object System.Drawing.Size
$System_Drawing_Size.Width = 70
$System_Drawing_Size.Height = 30
$button2.Size = $System_Drawing_Size
$button2.UseVisualStyleBackColor = $True
$button2.Text = "Exit"
$System_Drawing_Point = New-Object System.Drawing.Point
$System_Drawing_Point.X = 15
$System_Drawing_Point.Y = 160
$button2.Location = $System_Drawing_Point
$button2.DataBindings.DefaultDataSourceUpdateMode = 0
$button2.add_Click($handler_button2_Click)
$form1.Controls.Add($button2)
    #endregion $button2
    #region $textBox1
$System_Drawing_Size = New-Object System.Drawing.Size
$System_Drawing_Size.Width = 250
$System_Drawing_Size.Height = 20
$textBox1.Size = $System_Drawing_Size
$textBox1.DataBindings.DefaultDataSourceUpdateMode = 0
$textBox1.Name = "textBox1"
$System_Drawing_Point = New-Object System.Drawing.Point
$System_Drawing_Point.X = 15
$System_Drawing_Point.Y = 70
$textBox1.Location = $System_Drawing_Point
$textBox1.TabIndex = 1
$form1.Controls.Add($textBox1)
    #endregion $textBox1
    #region $textBox2
$System_Drawing_Size = New-Object System.Drawing.Size
$System_Drawing_Size.Width = 250
$System_Drawing_Size.Height = 20
$textBox2.Size = $System_Drawing_Size
$textBox2.DataBindings.DefaultDataSourceUpdateMode = 0
$textBox2.Name = "textBox2"
$System_Drawing_Point = New-Object System.Drawing.Point
$System_Drawing_Point.X = 15
$System_Drawing_Point.Y = 120
$textBox2.Location = $System_Drawing_Point
$textBox2.TabIndex = 2
$form1.Controls.Add($textBox2)
    #endregion $textBox2
    #region $comboBox1
$comboBox1.FormattingEnabled = $True
$System_Drawing_Size = New-Object System.Drawing.Size
$System_Drawing_Size.Width = 250
$System_Drawing_Size.Height = 21
$comboBox1.Size = $System_Drawing_Size
$comboBox1.DataBindings.DefaultDataSourceUpdateMode = 0
$comboBox1.Name = "comboBox1"
$System_Drawing_Point = New-Object System.Drawing.Point
$System_Drawing_Point.X = 15
$System_Drawing_Point.Y = 20
$comboBox1.Location = $System_Drawing_Point
$comboBox1.TabIndex = 0
$comboBox1.add_SelectedIndexChanged($handler_comboBox1_SelectedIndexChanged)

$comboBox1.DropDownStyle =
    [System.Windows.Forms.ComboBoxStyle]::DropDown;
$comboBox1.Sorted = $true;

$comboBox1.AutoCompleteCustomSource.Add("System.Windows.Forms");
$comboBox1.AutoCompleteCustomSource.AddRange(("System.Data", "Microsoft"));
$comboBox1.AutoCompleteMode =
    [System.Windows.Forms.AutoCompleteMode]::SuggestAppend;
$comboBox1.AutoCompleteSource =
    [System.Windows.Forms.AutoCompleteSource]::CustomSource;

$form1.Controls.Add($comboBox1)
    #endregion $comboBox1
#endregion Generated Form Code

#Save the initial state of the form
$InitialFormWindowState = $form1.WindowState
#Init the OnLoad event to correct the initial state of the form
$form1.add_Load($OnLoadForm_StateCorrection)
#Show the Form
$form1.ShowDialog()| Out-Null

} #End Function

#Call the Function
GenerateForm

Answer 1

Here is a q&d (quick and dirty) approach to what I am trying to recommend in my comment.

If you try and close the form via the WinForm 'X', the Windows 'Alt+F4', or even TaskMgrs' end task, it will warn you and simply restart for the user to try again.

Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Drawing
[System.Windows.Forms.Application]::EnableVisualStyles()


$form               = New-Object System.Windows.Forms.Form 
$form.Text          = 'New user GUI'
$form.Size          = New-Object System.Drawing.Size(300,200) 
$form.StartPosition = 'CenterScreen'

$OKButton              = New-Object System.Windows.Forms.Button
$OKButton.Location     = New-Object System.Drawing.Point(75,120)
$OKButton.Size         = New-Object System.Drawing.Size(75,23)
$OKButton.Text         = 'OK'
$OKButton.DialogResult = [System.Windows.Forms.DialogResult]::OK
$OKButton.Enabled      = $false

$form.AcceptButton = $OKButton
$form.Controls.Add($OKButton)

$label          = New-Object System.Windows.Forms.Label
$label.Location = New-Object System.Drawing.Point(10,20) 
$label.Size     = New-Object System.Drawing.Size(280,20) 
$label.Text     = 'Enter some stuff'

$form.Controls.Add($label) 

$textBox          = New-Object System.Windows.Forms.TextBox 
$textBox.Location = New-Object System.Drawing.Point(10,40) 
$textBox.Size     = New-Object System.Drawing.Size(260,20) 

$form.Controls.Add($textBox) 

$form.Topmost = $True
$form.Add_Shown({$textBox.Select()})

$textbox.Add_KeyDown(
    {$OKButton.Enabled = $True}
)

do
{
    $result = $form.ShowDialog()

    if ([string]::IsNullOrEmpty($textbox.text))
    {{[System.Windows.Forms.MessageBox]::Show('Please enter stuff, because I cannot proceed until you do.', 'Warning Message',1)}}
}
until(![string]::IsNullOrEmpty($textbox.text))

if ($result -eq [System.Windows.Forms.DialogResult]::OK)
{($UserInput = $textBox.Text)}

***Note:

Though I can see your goal here. This is not really a good user experience. Users should always be able to exit any app they are using to move on to other tasks.***

I can guarantee you, you are going to anger many with this use case.