Powershell Timer - Update gui

Question

I have created a powershell timer, and after every 1 second, I would like to run a function to execute or post text to a text box log on the interface.

Run the below. When you click Start, every 1 second, the log text area should show "Post to log every 1 second, not as a batch". However, this messages only appear as a batch, all at once, when you click Stop.

This question does not appear to be answered on the internet!

Code:

$global:timer = New-Object System.Timers.Timer
$global:timer.Interval = 1000


function AddToLog($logtext)
{
    $txtLog.Text = $txtLog.Text + "`r`n" + $logtext
    $txtLog.ScrolltoCaret
}

function startTimer() { 
    Register-ObjectEvent -InputObject $global:timer -EventName Elapsed -SourceIdentifier theTimer -Action {AddToLog('Post to log every 1 second, not as a batch') }
    $global:timer.start()
    Write-Host "Start Timer"
}

function stopTimer() {
    $global:timer.stop()
    Write-Host "Close Function"
    Unregister-Event theTimer
}


########################
# Setup User Interface
########################

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

$objForm = New-Object System.Windows.Forms.Form 
$objForm.Text = "Timer Example"
$objForm.Size = New-Object System.Drawing.Size(330,380) 
$objForm.StartPosition = "CenterScreen"


#Start Button
$btnStart = New-Object System.Windows.Forms.Button
$btnStart.Location = New-Object System.Drawing.Size(10,190)
$btnStart.Size = New-Object System.Drawing.Size(140,35)
$btnStart.Text = "Start"

$btnStart.Add_Click({StartTimer; })
$objForm.Controls.Add($btnStart)

#Stop Button
$btnStop = New-Object System.Windows.Forms.Button
$btnStop.Location = New-Object System.Drawing.Size(150,190)
$btnStop.Size = New-Object System.Drawing.Size(140,35)
$btnStop.Text = "Stop"
$btnStop.Add_Click({StopTimer; })
$objForm.Controls.Add($btnStop)
$btnStop.Enabled  = $true

#Log Area
$lblLog = New-Object System.Windows.Forms.Label
$lblLog.Location = New-Object System.Drawing.Size(10,230) 
$lblLog.Size = New-Object System.Drawing.Size(80,20) 
$lblLog.Text = "Event Log:"
$objForm.Controls.Add($lblLog) 

$txtLog = New-Object System.Windows.Forms.Textbox
$txtLog.Location = New-Object System.Drawing.Size(10,250)
$txtLog.Size = New-Object System.Drawing.Size(290,90)
$txtLog.Multiline = $True
$txtLog.Scrollbars = "vertical"

$txtLog.Add_Click({$txtLog.SelectAll(); $txtLog.Copy()})
$objForm.Controls.Add($txtLog)

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

Thanks for your help in advanced.

-R

Answer 1

I took what you had, and looked at this egg_timer project and came up with the following:

  $timer = New-Object System.Windows.Forms.Timer
  $timer.Interval = 1000
  $timer.add_tick({AddToLog 'Post to log every 1 second, not as a batch'})



function AddToLog($logtext)
{
    $txtLog.Text = $txtLog.Text + "`r`n" + $logtext
    $txtLog.ScrolltoCaret
}

function startTimer() { 

   $timer.start()

}

function stopTimer() {

    $timer.Enabled = $false
    Write-Host "Close Function"

}


########################
# Setup User Interface
########################

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

$objForm = New-Object System.Windows.Forms.Form 
$objForm.Text = "Timer Example"
$objForm.Size = New-Object System.Drawing.Size(330,380) 
$objForm.StartPosition = "CenterScreen"


#Start Button
$btnStart = New-Object System.Windows.Forms.Button
$btnStart.Location = New-Object System.Drawing.Size(10,190)
$btnStart.Size = New-Object System.Drawing.Size(140,35)
$btnStart.Text = "Start"

$btnStart.Add_Click({StartTimer; })
$objForm.Controls.Add($btnStart)

#Stop Button
$btnStop = New-Object System.Windows.Forms.Button
$btnStop.Location = New-Object System.Drawing.Size(150,190)
$btnStop.Size = New-Object System.Drawing.Size(140,35)
$btnStop.Text = "Stop"
$btnStop.Add_Click({StopTimer; })
$objForm.Controls.Add($btnStop)
$btnStop.Enabled  = $true

#Log Area
$lblLog = New-Object System.Windows.Forms.Label
$lblLog.Location = New-Object System.Drawing.Size(10,230) 
$lblLog.Size = New-Object System.Drawing.Size(80,20) 
$lblLog.Text = "Event Log:"
$objForm.Controls.Add($lblLog) 

$txtLog = New-Object System.Windows.Forms.Textbox
$txtLog.Location = New-Object System.Drawing.Size(10,250)
$txtLog.Size = New-Object System.Drawing.Size(290,90)
$txtLog.Multiline = $True
$txtLog.Scrollbars = "vertical"

$txtLog.Add_Click({$txtLog.SelectAll(); $txtLog.Copy()})
$objForm.Controls.Add($txtLog)


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

Answer 2

Try using a System.Windows.Forms.Timer. See this article for info on the differences between .NET timers.

In the case of a WinForms timer, ditch the Register-ObjectEvent and Unregister-Event and add this line before you call ShowDialog():

$timer.add_Tick({AddToLog('Post to log every 1 second, not as a batch')})

Don't forget to change to System.Windows.Forms.Timer. When I make those change, the UI works.

Use of Register-ObjectEvent requires that PowerShell services the event queue at various safe points in its execution. However, since PowerShell is blocked inside some .NET code (Form.ShowDialog()), it doesn't get a chance to service its event queue.