winforms - In PowerShell Form.Show() does not work right, but Form.ShowDialog() does

Question

I am trying to display an image via powershell. I made a script based on this forum post.

If I use ShowDialog() it works fine, except the powershell execution stops while the dialog is up. However, that is by design for a modal dialog. If I call Form.Show() in PowershellISE the form shows up, but freezes and cannot be moved or dismissed. Behavior is similar if I copy and past the code to a powershell console.

How do I make the dialog non-modal, and not freeze.

Answer 1

First Answer Why it appends.

In a Windows graphic program the thread which create a Window must loop in a message pump in order to redistribute (translate) messages coming from the user action to events in his Windows.

In a modal window, the modal code that handles the window display runs its own message pump loop and doesn't return until the window is closed. That's why the code after ShowDialog() won't execute until the window is closed.

Show(), just ask to show the Window, but if there is no pump loop to manage the messages coming from user action, it just freezes.

Second a simple way to have two threads

The CmdLet start-job use another thread from the pool allocated by Powershell so it makes the dialog non-modal, and it does not freeze.

function goForm
{
  [void][reflection.assembly]::LoadWithPartialName("System.Windows.Forms")

  $file = (get-item 'C:empjpb.png')
  #$file = (get-item "c:image.jpg")

  $img = [System.Drawing.Image]::Fromfile($file);

  # This tip from http://stackoverflow.com/questions/3358372/windows-forms-look-different-in-powershell-and-powershell-ise-why/3359274#3359274
  [System.Windows.Forms.Application]::EnableVisualStyles();
  $form = new-object Windows.Forms.Form
  $form.Text = "Image Viewer"
  $form.Width = $img.Size.Width;
  $form.Height =  $img.Size.Height;
  $pictureBox = new-object Windows.Forms.PictureBox
  $pictureBox.Width =  $img.Size.Width;
  $pictureBox.Height =  $img.Size.Height;

  $pictureBox.Image = $img;
  $form.controls.add($pictureBox)
  $form.Add_Shown( { $form.Activate() } )
  $form.ShowDialog()
}

Clear-Host

start-job $function:goForm

$name = Read-Host "What is you name"
Write-Host "your name is $name"