combobox trigger

PowerShell Help
1

I’m stumped. Have a form with a ComboBox on it that holds two items. What I want is if I change the selected item in that ComboBox, some stuff happens. But there’s no trigger built into the ComboBox control that I can find. I found one article and it looks like they created a trigger, but I don’t understand how or why it works. Applicable lines of code:

$cbx_Campus = New-Object System.Windows.Forms.ComboBox
$cbx_Campus.OnTextUpdate(
{$campus = $cbx_Campus.Text; write-host "campus = $campus" }
) 
$frm_CampusVar.Controls.Add($cbx_Campus)

Error: [System.Windows.Forms.ComboBox] doesn’t contain a method named ‘OnTextUpdate’.

When I get-member on a ComboBox object, it lists “OnTextUpdate” as an event for ComboBox. So why is it not working?

Thanks in advance for your help.

2

According to Get-Member, the event name is just TextUpdate, not OnTextUpdate. There’s also a TextChanged event, though; I’d recommend checking the MSDN documentation to find out which event meets your needs.

3

I tried the following code. It didn’t throw an error, but neither did it do anything.

   if ($cbx_Campus.TextUpdate) {
      write-host "campus = $cbx_campus.text"
      }
4

Somebody put this code up on the web. Looks like they manufactured an event trigger that works. But I’m not sure why it works or how to incorporate it in my script.

$Form1 = New-Object System.Windows.Forms.Form
$Form1.ClientSize = New-Object System.Drawing.Size(200, 200)
$form1.topmost = $true
 
$comboBox1 = New-Object System.Windows.Forms.ComboBox
$comboBox1.Location = New-Object System.Drawing.Point(25, 55)
$comboBox1.Size = New-Object System.Drawing.Size(150, 150)
$comboBox1.Items.add("Test1")
$comboBox1.Items.add("Test2")
$Form1.Controls.Add($comboBox1)
 
# -------------------------------------------------------------------------------
#                             Change triggered function
# -------------------------------------------------------------------------------
 
$ComboBox1_SelectedIndexChanged=
{
   If ($ComboBox1.text -eq "Test1") {Write-host "Test1 chosen"}
   Else {Write-host "Test2 chosen"}
}
################ MUST CREATE BEFORE ASSIGN ################
$ComboBox1.add_SelectedIndexChanged($ComboBox1_SelectedIndexChanged)
 
[void]$form1.showdialog()

Specifically, I don’t know where the “add_SelectedIndexChanged” part comes from on this line: $ComboBox1.add_SelectedIndexChanged($ComboBox1_SelectedIndexChanged)

5

Your original code was closer to what you’d need to do:

$cbx_Campus = New-Object System.Windows.Forms.ComboBox
$cbx_Campus.add_TextUpdate(
    {$script:campus = $cbx_Campus.Text; write-host "campus = $campus" }
) 
$frm_CampusVar.Controls.Add($cbx_Campus)

Notice that I added a $script: scope modifier to your variable assignment within the event handler. Otherwise, you’d be assigning a value to a local $campus variable within the handler block, and it wouldn’t be accessible to the rest of your code later.

6

Yep, you’re on the right track there. They’re using a different event (SelectedIndexChanged instead of TextUpdate), but the basic code is the same. You call the add_EventName() method and pass in a script block.

7

Got it. Figured sleep would help.

$cbx_Campus_SelectedIndexChanged=
{
$script:campus = $cbx_Campus.Text
If ($script:Campus -eq “RGC”) {Write-host “RGC chosen”}
Else {Write-host “HLC chosen”}
}
################ MUST CREATE BEFORE ASSIGN ################
$cbx_Campus.add_SelectedIndexChanged($cbx_Campus_SelectedIndexChanged)

Thanks for the explanation about how add_EventName() method works.

8

Here is a modified example that seems to work. Two buttons are added to process the selected item and clear the form.

#region Form
[void] [System.Reflection.Assembly]::LoadWithPartialName(“System.Drawing”)
[void] [System.Reflection.Assembly]::LoadWithPartialName(“System.Windows.Forms”)

$Form1 = New-Object System.Windows.Forms.Form
$Form1.ClientSize = New-Object System.Drawing.Size(200, 200)
$form1.topmost = $true
#endregion Form

#region Functions
Function Clear-Form{
$ComboBox1.SelectedIndex = -1
$ComboBox1.SelectedItem = “”
Clear-Host
}

Function Test-Something{
If ($ComboBox1.SelectedItem -lt 0){
$Selected = “No selection was made”
Write-host $Selected -ForegroundColor Red

}
Else {
$Selected = $ComboBox1.SelectedItem.ToString()
Write-host “$Selected chosen” -ForegroundColor Green
}
Return $Selected
}
#endregion Functions

#region Dropdown
$comboBox1 = New-Object System.Windows.Forms.ComboBox
$comboBox1.Location = New-Object System.Drawing.Point(20, 20)
$comboBox1.Size = New-Object System.Drawing.Size(150, 150)
$comboBox1.Items.add(“Test1”)
$comboBox1.Items.add(“Test2”)
$Form1.Controls.Add($comboBox1)
#endregion Dropdown

#region Buttons
#region TEST Button1
$TestButton1 = New-Object System.Windows.Forms.Button
$TestButton1.Location = New-Object System.Drawing.Size(20,50)
$TestButton1.Size = New-Object System.Drawing.Size(50,50)
$TestButton1.ForeColor = “White”
$TestButton1.BackColor = “Green”
$TestButton1.Text = “Test”
$TestButton1.Add_Click({Test-Something}) #Test-Something
$Form1.controls.Add($TestButton1)
#endregion TEST Button1

#region TEST Button1
	$ClearButton = New-Object System.Windows.Forms.Button 
	$ClearButton.Location = New-Object System.Drawing.Size(90,50) 
	$ClearButton.Size = New-Object System.Drawing.Size(50,50)
	$ClearButton.ForeColor = "Black"
	$ClearButton.BackColor = "White"
	$ClearButton.Text = "Clear" 
	$ClearButton.Add_Click({Clear-Form})
	$Form1.controls.Add($ClearButton)
#endregion TEST Button1

#endregion Buttons

[void]$form1.showdialog()