Global Variables from WinForm - function

Question

I am currently trying to use the values of a date/time picker variable from one function and use it multiple times in another function. The date/time picker is on a form, so when a user sets a start date and end date, those values are assigned to a variable to use in the other function, which should call both those variables at least twice. While trying to call that variable from the first function, it contains a null value even though it was assigned to a variable. I am trying to keep the value that was created in one function to use in another function multiple times. Thank you.
Set-strictMode -off
[void][System.Reflection.Assembly]::LoadWithPartialName("System.windows.forms")
[System.Windows.Forms.Application]::EnableVisualStyles()
Add-Type -AssemblyName System.Web
[Net.ServicePointManager]::SecurityProtocol = "tls12, tls11, tls"
$global:startDate=$null
$global:endDate=$null
function MakeForm{
#region begin GUI
$Form = New-Object system.Windows.Forms.Form
$Form.ClientSize = '396,180'
$Form.text = "Rexpii Integrations Version (Beta)"
$Form.BackColor = "#ffffff"
$Form.TopMost = $False
$Form.Icon= [System.Drawing.Icon]::ExtractAssociatedIcon('C:\files\scripts\tpgicon.ico')
$btnSubmit = New-Object system.Windows.Forms.Button
$btnSubmit.text = "Submit"
$btnSubmit.width = 60
$btnSubmit.height = 30
$btnSubmit.location = New-Object System.Drawing.Point(220,116)
$btnSubmit.Font = 'Microsoft Sans Serif,10'
$btnSubmit.Add_Click({
$global:startDate= $Global:txtStartDate.Value.ToString("yyyy-MM-dd")
$global:endDate= $Global:txtEndDate.Value.ToString("yyyy-MM-dd")
GetData
$Form.Close()})
$btnCancel = New-Object system.Windows.Forms.Button
$btnCancel.text = "Cancel"
$btnCancel.width = 60
$btnCancel.height = 30
$btnCancel.location = New-Object System.Drawing.Point(288,116)
$btnCancel.Font = 'Microsoft Sans Serif,10'
$btnCancel.Add_Click({
$Form.Close()
})
$Global:txtStartDate = New-Object system.Windows.Forms.DateTimePicker
$Global:txtStartDate.width = 150
$Global:txtStartDate.location = New-Object System.Drawing.Point(208,40)
$Global:txtStartDate.Format = "Custom"
$Global:txtstartDate.CustomFormat = "yyyy-MM-dd"
$Global:txtEndDate = New-Object system.Windows.Forms.DateTimePicker
$Global:txtEndDate.width = 150
$Global:txtEndDate.location = New-Object System.Drawing.Point(208,80)
$Global:txtEndDate.Format="Custom"
$Global:txtEndDate.CustomFormat = "yyyy-MM-dd"
$Form.controls.AddRange(#($btnSubmit,$btnCancel,$PictureBox1,$PictureBox2,$StartDate,$EndDate,$lblStartDate,$lblEndDate,$txtStartDate, $txtEndDate))
[void]$Form.ShowDialog()
}
MakeForm
function GetData{
#my scripts number one
Write-Output "This is the first $global:startDate to $global:endDate example"
#my scripts number two
Write-Output "This is the second $global:startDate to $global:endDate example"
}

Answer 1

First, you need to define your functions before you can use them. You are trying to call GetData before it's defined. Move the call to MakeForm (which also shows the form) to after the function definition for GetData.
Second, should change GetData to call Write-Host instead of Write-Output so you can see the output from the event handler. And if you call GetData after showing the form, you'll see that the globals are set properly.
So the last part of your script should look like:
function GetData{
#my scripts number one
Write-Host "This is the first $global:startDate to $global:endDate example"
#my scripts number two
Write-Host "This is the second $global:startDate to $global:endDate example"
}
MakeForm
# Call GetData again to verify that the globals are set.
GetData