Powershell : When event handler is inside for loop, Checkbox change event does not give valid result

Question

I created an array of Check boxes. I could create a event handler for each check box separately but as it would be lengthy code I thought if I could create them using loop. When event handler is written inside loop the event is being handled but the result shown is wrong i.e -> when I select i'th check box the event is handled but $checkBox_Charts[$i].Checked is always returning False whether the box is checked or unchecked.

Edit 1:

I realized even when checked event is raised on any check box this code is returning checked status of last element in for loop,
Adding the complete code

Code:

function whichCharts(){
    Write-Host "CP1: in whichCharts"
    foreach ($key_chart in $charts.Keys){
        Write-Host $charts[$key_chart]
    }
}

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

# Set the size of your form
$Form = New-Object System.Windows.Forms.Form
$Form.width = 1000
$Form.height = 600
$Form.Text = ”My First Form with a working checkbox”

# Set the font of the text to be used within the form
$Font = New-Object System.Drawing.Font("Times New Roman",12)
$Form.Font = $Font



$charts = @("x","y","z")

$checkBox_Charts =[System.Windows.Forms.checkbox[]]::new(3)

$index_checkBox_Charts=0
for ($i=0;$i -lt $charts.Count; $i++){
$CheckBox = new-object System.Windows.Forms.checkbox
    $height = (60*$i)+20
    $CheckBox.Location = new-object System.Drawing.Size(100,$height)
$CheckBox.Size = '150,50'
$CheckBox.Text = $charts[$i]
$CheckBox.Checked = $false
$checkBox_Charts[$i] = $CheckBox

}



# Add an OK button
$OKButton = new-object System.Windows.Forms.Button
$OKButton.Location = '50,500'
$OKButton.Size = '100,40'
$OKButton.Text = "OK"
$OKButton.DialogResult=[System.Windows.Forms.DialogResult]::OK

#Add a cancel button
$CancelButton = new-object System.Windows.Forms.Button
$CancelButton.Location = '255,100'
$CancelButton.Size = '100,40'
$CancelButton.Text = "Cancel"
$CancelButton.DialogResult=[System.Windows.Forms.DialogResult]::Cancel

# Create a group that will contain your radio buttons
$MyGroupBox = New-Object System.Windows.Forms.GroupBox
$MyGroupBox.Location = '40,30'
$MyGroupBox.size = '800,400'
$MyGroupBox.text = "Do you like Cheese?"

# Add all the GroupBox controls on one line
$MyGroupBox.Controls.AddRange(@($checkBox_Charts))

$Form.Controls.AddRange(@($MyGroupBox,$OKButton,$CancelButton))
###########  This is the important piece ##############
#                                                     #
# Do something when the state of the checkbox changes #
#######################################################

for($i=0; $i -lt 2; $i++){
    $checkBox_Charts[$i].Add_CheckStateChanged({
    Write-Host "CP2: in Add_CheckStateChanged " + $checkBox_Charts[$i].Checked
    Write-Host $checkBox_Charts[$i]
    Write-Host $i})

}



# Activate the form
$Form.Add_Shown({$Form.Activate()})
[void] $Form.ShowDialog() 
}



#Call the function
checkbox_test

Can you give me some test data to fill this with?

ArcSet
– ArcSet

2020-04-04 18:18:26 +00:00
Commented Apr 4, 2020 at 18:18 — ArcSet
– ArcSet, Commented Apr 4, 2020 at 18:18
Code sample is incomplete, where is $charts defined?

Mathias R. Jessen
– Mathias R. Jessen

2020-04-04 19:21:03 +00:00
Commented Apr 4, 2020 at 19:21 — Mathias R. Jessen
– Mathias R. Jessen, Commented Apr 4, 2020 at 19:21
yes charts is defined

sql_dummy
– sql_dummy

2020-04-04 19:33:22 +00:00
Commented Apr 4, 2020 at 19:33 — sql_dummy
– sql_dummy, Commented Apr 4, 2020 at 19:33
@ArcSet I have added complete code, please check on it.

sql_dummy
– sql_dummy

2020-04-05 08:05:18 +00:00
Commented Apr 5, 2020 at 8:05 — sql_dummy
– sql_dummy, Commented Apr 5, 2020 at 8:05

Theo · Accepted Answer · 2020-04-05 13:33:51Z

Inside the scriptblock for the CheckStateChanged event, the variable $i is unknown. To make its value available there, you must have stored it in a property the checkbox can read. The best place for this is the checkbox's own Tag property.

In your code, create the checkboxes like this:

$charts = "x","y","z"   # no need to surround this with @()

$checkBox_Charts = [System.Windows.Forms.checkbox[]]::new($charts.Count)
for ($i = 0; $i -lt $charts.Count; $i++){
    $CheckBox = new-object System.Windows.Forms.checkbox
    $height = (60*$i)+20
    $CheckBox.Location = new-object System.Drawing.Size(100,$height)
    $CheckBox.Size = '150,50'
    $CheckBox.Text = $charts[$i]
    $CheckBox.Checked = $false
    # save the index $i in the Tag property of the checkbox itself
    $CheckBox.Tag = $i
    $CheckBox.Add_CheckStateChanged({
        # inside this scriptblock, the variable $i is unknown
        # so we use the index value stored in the Tag property earlier
        Write-Host "CP2: in Add_CheckStateChanged $($this.Checked)"
        Write-Host "CheckBox index: $($this.Tag)"
        Write-Host $checkBox_Charts[$this.Tag]
        Write-Host
    })
    $checkBox_Charts[$i] = $CheckBox
}

Then remove the code you have here:

###########  This is the important piece ##############
#                                                     #
# Do something when the state of the checkbox changes #
#######################################################

for($i=0; $i -lt 2; $i++){
    $checkBox_Charts[$i].Add_CheckStateChanged({
    Write-Host "CP2: in Add_CheckStateChanged " + $checkBox_Charts[$i].Checked
    Write-Host $checkBox_Charts[$i]
    Write-Host $i})

}

because this is now all done while creating the checkboxes earlier (and won't work as you have noticed)

As sidenotes:

change this obsolete/deprecated code:

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

into

Add-Type -AssemblyName System.Windows.Forms Add-Type -AssemblyName System.Drawing

straighten the curly quotes you have in $Form.Text = ”My First Form with a working checkbox” to become $Form.Text = "My First Form with a working checkbox".
They won't hurt you in this case, but using curly quotes in code can lead to numerous weird problems. Never use them in code.

^{Inside a control's event handler, the $this automatic variable refers to the control itself}

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