Using Powershell GUI + Refresh

I'm struggling here.

Take this sample code:

[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Drawing") 
[void] [System.Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms") 

$objForm = New-Object System.Windows.Forms.Form 
$objForm.Text = "Data Entry Form"
$objForm.Size = New-Object System.Drawing.Size(500,400) 
$objForm.StartPosition = "CenterScreen"

$objForm.KeyPreview = $True
$objForm.Add_KeyDown({if ($_.KeyCode -eq "Enter") 
    {$output1=$objTextBox.Text}})
$objForm.Add_KeyDown({if ($_.KeyCode -eq "Escape") 
    {$objForm.Close()}})

$OKButton = New-Object System.Windows.Forms.Button
$OKButton.Location = New-Object System.Drawing.Size(100,90)
$OKButton.Size = New-Object System.Drawing.Size(75,23)
$OKButton.Text = "Merge"
$OKButton.Add_Click({$output=$objTextBox.Text})
$objForm.Controls.Add($OKButton)

$CancelButton = New-Object System.Windows.Forms.Button
$CancelButton.Location = New-Object System.Drawing.Size(300,90)
$CancelButton.Size = New-Object System.Drawing.Size(75,23)
$CancelButton.Text = "Cancel"
$CancelButton.Add_Click({$objForm.Close()})
$objForm.Controls.Add($CancelButton)

$objLabel = New-Object System.Windows.Forms.Label
$objLabel.Location = New-Object System.Drawing.Size(160,20) 
$objLabel.Size = New-Object System.Drawing.Size(280,20) 
$objLabel.Text = "Please enter the target machine: "
$objForm.Controls.Add($objLabel) 

$output = new-object System.Windows.forms.label
$output.location = new-object System.drawing.size(30, 140)
$output.size = New-Object System.Drawing.Size(300,300) 
$objform.controls.add($output)

$objTextBox = New-Object System.Windows.Forms.TextBox 
$objTextBox.Location = New-Object System.Drawing.Size(115,40) 
$objTextBox.Size = New-Object System.Drawing.Size(260,20) 
$objForm.Controls.Add($objTextBox) 

$objForm.Topmost = $True

$objForm.Add_Shown({$objForm.Activate()})
[void] $objForm.ShowDialog()
$output

I can't for the life of me figure out why when I enter text into the box and click the OKButton (Merge) nothing happns. It should be outputted to the $output, or at least, thats what I want to happen.

I'm simply trying to get the code to take the input of the text box and output it to the label form called $output.

I've got it to work in the sense that when I put input into the text box and press 'Merge', it outputs it to the Powershell_ISE console, but only after the window is closed and in run for a second time (It's not refreshing the $output label when I press 'merge' and only outputs when I close the program)

Please help!

Thank you