powershell: change GUI element when async FileSystemWatcher fires - powershell

Question

I like to change a GUI element (windows-form in powershell ISE), when a new file is created. Therefore I set up a form and start a filesystemwatcher in another runspace (MWE):
# this function should be called when a new file is created
function foobar(){
$form.BackColor = "black"
}
# set up runspace for async FileSystemWatcher
$Runspace = [runspacefactory]::CreateRunspace()
$PowerShell = [System.Management.Automation.PowerShell]::Create()
$PowerShell.runspace = $Runspace
$Runspace.Open()
[void]$PowerShell.AddScript({
$logFile = 'C:\powershell\test.log'
$dirName = 'C:\powershell\'
$hotFolder = New-Object IO.FileSystemWatcher $dirName -Property #{IncludeSubdirectories = $false;NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite'}
Register-ObjectEvent $hotFolder Created -SourceIdentifier FileCreated -Action {
$name = $Event.SourceEventArgs.Name
$path = $Event.SourceEventArgs.FullPath
$changeType = $Event.SourceEventArgs.ChangeType
$timeStamp = $Event.TimeGenerated
Out-File -FilePath $logFile -Append -InputObject "The file '$name' was $changeType at $timeStamp"
# this call does not work
foobar
}
})
$AsyncObject = $PowerShell.BeginInvoke()
# set up form
$form = New-Object System.Windows.Forms.Form
$form.ShowDialog()
The FileSystemWatcher works (log-file is written), but the call of "foobar" is ignored / does not work.
My first try was to Register the FileSystemWatcher within the form, which does not work (similar to this: FileSystemWatcher and GUI). I found this thread FileSystemWatcher kommt nicht mit Form zurecht (german only), which suggests the use of runspaces.
The runspace solves the stuck GUI-problem, but I need a way to trigger events in the form, when the fileSystemWatcher registers a new file. How can I achive that?
in short:
1) how can the FileSystemWatcher trigger a change of a GUI-element
2) are runspaces the right approach in this case
I'm not an expert in powershell (still learning). Any help and suggestions are appreciated.
Thanks in advance.

Answer 1

I did some research and found a solution:
added a synchronized hashtable to share variables between runspaces
added a button of the form to the hashtable (this button will be hidden in the final version drawing.Size(0,0) )
fileSystemWatcher makes use of performclick() to click the button
button calls desired function on click
There is still a point which feel awkward:
to unregister the fileSystemWatcher I set a shared variable to 1 and trigger the fileSystemWatcher by generating a file
Is there a more elegant way to do this?
Do I miss some points where the code is unnecessarily complicated?
Any comments are appreciated.
Here is a MWE. To use it set the $dir variable to your need. (MWE does not work in not updated powershell which ships with Win7)
# set working dir
$dir = 'C:\Downloads'
Write-Host 'working dir' $dir
# create function which is called when new file is created
function showPath($path){
$label.Text = $path
}
# set up runspace for async FileSystemWatcher
$Runspace = [runspacefactory]::CreateRunspace()
$Runspace.Open()
# synchronized hashtable and hashtable elements
$sync = [Hashtable]::Synchronized(#{})
$sync.path = 1 # random start value
$sync.exit = 0 # switch: if set to 1 fileSystemWatcher will be unregistert when next event occurs
$sync.dir = $dir
$btnNewFile= New-Object System.Windows.Forms.Button
$btnNewFile.Location = New-Object System.Drawing.Size(220,10)
$btnNewFile.Size = New-Object System.Drawing.Size(150,23)
$btnNewFile.Text = "do not click - fake button"
$btnNewFile.Add_Click({
$newPath = $sync.path
$form.text = $newPath
showPath($newPath)
})
$sync.btnNewFile = $btnNewFile
$Runspace.SessionStateProxy.SetVariable("sync", $sync)
$PowerShell = [System.Management.Automation.PowerShell]::Create()
$PowerShell.runspace = $Runspace
[void]$PowerShell.AddScript({
$logFile = Join-Path $sync.dir test.log
$dirName = $sync.dir
$hotFolder = New-Object IO.FileSystemWatcher $dirName -Property #{IncludeSubdirectories = $false;NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite'}
Register-ObjectEvent $hotFolder Created -SourceIdentifier FileCreated -Action {
$path = $Event.SourceEventArgs.FullPath
$name = $Event.SourceEventArgs.Name
$changeType = $Event.SourceEventArgs.ChangeType
$timeStamp = $Event.TimeGenerated
# check if exit condition is met
if($sync.exit -eq 1){
Out-File -FilePath $logFile -Append -InputObject "Exit file: '$name'"
Unregister-Event FileCreated
}
else{
Out-File -FilePath $logFile -Append -InputObject "The file '$name' was $changeType at $timeStamp"
# set path to synchroniszed variable
$sync.path = $path
# click Button to trigger function call
$sync.btnNewFile.PerformClick()
}
}
})
$AsyncObject = $PowerShell.BeginInvoke()
# GUI setup
$labelHeader = New-Object System.Windows.Forms.Label
$labelHeader.Location = New-Object System.Drawing.Size(10,50)
$labelHeader.Size = New-Object System.Drawing.Size(100,23)
$labelHeader.Text = 'path to new file:'
$label = New-Object System.Windows.Forms.Label
$label.Location = New-Object System.Drawing.Size(110,50)
$label.Size = New-Object System.Drawing.Size(200,23)
$label.Text = 'no file created'
$global:fileCounter = 0
$btnCreateFile = New-Object System.Windows.Forms.Button
$btnCreateFile.Location = New-Object System.Drawing.Size(10,10)
$btnCreateFile.Size = New-Object System.Drawing.Size(100,23)
$btnCreateFile.Text = "New File"
$btnCreateFile.Add_Click({
$global:fileCounter+=1
$fileName = "$global:fileCounter.txt"
$newFile = Join-Path $dir $fileName
New-Item $newFile -ItemType file
})
$btnExit = New-Object System.Windows.Forms.Button
$btnExit.Location = New-Object System.Drawing.Size(110,10)
$btnExit.Size = New-Object System.Drawing.Size(100,23)
$btnExit.Text = "&Exit"
$btnExit.Add_Click({
$sync.Exit = 1
$btnCreateFile.PerformClick()
$Powershell.Dispose()
$form.Close()
})
# set up form
$form = New-Object System.Windows.Forms.Form
$form.Width = 400
$form.Height = 120
$form.Controls.Add($btnCreateFile)
$form.Controls.Add($btnExit)
$form.Controls.Add($labelHeader)
$form.Controls.Add($label)
$form.Controls.Add($sync.btnNewFile)
$form.ShowDialog()

Answer 2

I really like your solution, but the problem, like you say, is not working for PS2.0, including the service pack 1 for Win7, where I need.
My solution for the GUI update works both in PS2(win7) and in PS3(win10), it is based in Windows Presentation Framework(WPF) instead Windows Forms, because with WPF we can use Data Binding and the INotifyPropertyChanged interface. I have based my work in Trevor Jones web How-To ,with some tricks to get work.
For your question about Unregister the system I have translated, from VB to PS, a post from Mike Ober in SpiceWorks, in which his concept to Register and Unregister the system based in global variables and possible errors inspired me.
Here is my code:
Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase
Function Create-WPFWindow {
Param($Hash)
# Create a window object
$Window = New-Object System.Windows.Window
$Window.Width = '600'
$Window.Height = '300'
$Window.Title = 'WPF-CONTROL'
$window.WindowStartupLocation = [System.Windows.WindowStartupLocation]::CenterScreen
$Window.ResizeMode = [System.Windows.ResizeMode]::NoResize
# Create a Label object
$Label = New-Object System.Windows.Controls.Label
$Label.Height = 40
$Label.HorizontalContentAlignment = 'Left'
$Label.VerticalContentAlignment = 'Center'
$Label.FontSize = 15
$Label.Content = 'Actividad:'
$Hash.Label = $Label
# Create a TextBlock object
$TextBlock = New-Object System.Windows.Controls.TextBlock
$TextBlock.Height = 150
$TextBlock.FontSize = 20
$TextBlock.TextWrapping = 'Wrap'
$Hash.TextBlock = $TextBlock
# Create a Button1 object
$Button1 = New-Object System.Windows.Controls.Button
$Button1.Width = 300
$Button1.Height = 35
$Button1.HorizontalContentAlignment = 'Center'
$Button1.VerticalContentAlignment = 'Center'
$Button1.FontSize = 20
$Button1.Content = 'Iniciar'
$Hash.Button1 = $Button1
# Assemble the window
$StackPanel1 = New-Object System.Windows.Controls.StackPanel
$StackPanel1.Margin = '150,20,5,5'
$StackPanel1.Orientation = 'Horizontal'
$StackPanel1.Children.Add($Button1)
$StackPanel2 = New-Object System.Windows.Controls.StackPanel
$StackPanel2.Margin = '5,5,5,5'
$StackPanel2.Orientation = 'Vertical'
$StackPanel2.Children.Add($Label)
$StackPanel2.Children.Add($TextBlock)
$StackPanel = New-Object System.Windows.Controls.StackPanel
$StackPanel.Margin = '5,5,5,5'
$StackPanel.Children.Add($StackPanel1)
$StackPanel.Children.Add($StackPanel2)
$Window.Content = $StackPanel
# Stop the service and release the resources
$Window.Add_Closing({
$Hash.On = $false
$global:p.BeginInvoke()
$global:p.Dispose()})
$Hash.Window = $Window
}
$Hash = [hashtable]::Synchronized(#{})
# Create a WPF window and add it to a Hash table
Create-WPFWindow $Hash | Out-Null
# Create a datacontext for the TextBlock, we add it to the synchronized $Hash to update the GUI from the FileSystemWatcher Event.
$DataContext = New-Object System.Collections.ObjectModel.ObservableCollection[Object]
$Text = [string]'Pulse el botón para iniciar el sistema.'
$DataContext.Add($Text)
$Hash.TextBlock.DataContext = $DataContext
$Hash.DataContext = $DataContext
$Hash.path='C:\POWERSHELL_PROJECT\Result'
# These two vars are for my needs, you can obviate them or delete
$Hash.urlLOGIN=''
$Hash.urlLOTE=''
$Hash.fileWatcher = $null
$Hash.LOG='C:\POWERSHELL_PROJECT\Result\LOG.log'
$Hash.firstEvent = $false
$Hash.On=$false
$Hash.msg=''
# Create and set a binding on the TextBlock object
$Binding = New-Object System.Windows.Data.Binding -ArgumentList '[0]'
$Binding.Mode = [System.Windows.Data.BindingMode]::OneWay
[void][System.Windows.Data.BindingOperations]::SetBinding($Hash.TextBlock,[System.Windows.Controls.TextBlock]::TextProperty, $Binding)
# Add an event for the Button1 click to Register FileSystemWatcher and Unregister it
$Hash.Button1.Add_Click({
if ($Hash.On -eq $true){
$Hash.On = $false
$Hash.Button1.Background = 'Green'
$Hash.Button1.Content = 'Iniciar'
}else{
$Hash.On = $true
$Hash.Button1.Background = 'Red'
$Hash.Button1.Content = 'Detener'
}
$p.BeginInvoke() | Out-Null
})
# Multithreading runspaces for FileSystemWatcher
$rs_dForm = [Management.Automation.Runspaces.RunspaceFactory]::CreateRunspace()
$rs_dForm.ApartmentState = 'STA'
$rs_dForm.ThreadOptions = 'ReuseThread'
$rs_dForm.Open()
$rs_dForm.SessionStateProxy.SetVariable('Hash', $Hash)
$p = [PowerShell]::Create().AddScript({
Function global:OnFileSystemWatcherError {
FileEventListener -Path $Hash.path
}
# With simple function we can refresh the Textbox and Log
Function global:Refresh-WPF-and-LOG {
$Hash.DataContext[0] = $Hash.msg
echo $Hash.msg >> $Hash.LOG
}
Function global:FileEventListener ($Path){
if ($Hash.On){
$Hash.fileWatcher = New-Object System.IO.FileSystemWatcher
$Hash.fileWatcher.Path = $Path
$Hash.fileWatcher.Filter = '*.xml'
$Hash.fileWatcher.IncludeSubdirectories = $false
$Hash.fileWatcher.InternalBufferSize = 32768
$Hash.fileWatcher.EnableRaisingEvents=$true
Register-ObjectEvent -InputObject $Hash.fileWatcher -EventName Changed -SourceIdentifier File.Changed -Action {
$Global:t = $event
if (!$Hash.firstEvent){
try{
# For example you can:
$Hash.msg = '[' + $(Get-Date -Format u | foreach {$_ -replace ' ','-'}).ToString() + ']--' + $event.SourceEventArgs.Name
}catch{
$Hash.msg = '[' + $(Get-Date -Format u | foreach {$_ -replace ' ','-'}).ToString() + ']--' + $_.Exception.Message + ' ' + $_.Exception.ItemName
}finally{
Refresh-WPF-and-LOG
}
$Hash.firstEvent=$true
}else{
$Hash.firstEvent=$false
}
}
# With this Register we control the errors from the FileSystemWatcher system, and reinit it this case
Register-ObjectEvent -InputObject $Hash.fileWatcher -EventName Error -SourceIdentifier File.Error -Action {
$Global:t = $event
$Hash.On = $false
OnFileSystemWatcherError
}
$Hash.msg = '[' + $(Get-Date -Format u | foreach {$_ -replace ' ','-'}).ToString() + ']--' + 'Servicio INICIADO.'
}else{
if ( $Hash.fileWatcher -ne $null ){
$Hash.fileWatcher.EnableRaisingEvents=$false
Unregister-Event File.Changed
Unregister-Event File.Error
$Hash.fileWatcher.Dispose()
$Hash.fileWatcher=$null
$Hash.msg='[' + $(Get-Date -Format u | foreach {$_ -replace ' ','-'}).ToString() + ']--' + 'Sistema DETENIDO.'
}
}
Refresh-WPF-and-LOG
}
FileEventListener -Path $Hash.path
})
$p.Runspace = $rs_dForm
# Show the window
$Hash.Window.ShowDialog() | Out-Null
I hope to help.