Adafruit USB + Serial RGB Backlight Character LCD Backpack VBScript API

System Requirements:

  • Adafruit USB Serial RGB Backlight Character LCD Backpack

The Problem:

I recently needed a fast, cheap and modular way to output small amounts of information from a headless Windows 7 appliance, something that didn’t require a large amount of electrical engineering work or assembly while at the same time working over USB.

I accidentally stumbled upon a product by Adafruit, who seem to be tightly aligned with the Raspberry Pi/Arduino, however USB is USB which means that making it cooperate with Win32 wouldn’t be particularly challenging.

Being the lazy person that I am, I never much care for the idea of having to repeatedly type out control commands through a command line parser to get what I want and quite frankly, getting a NT Command Prompt to reliably pass anything out to a Serial Port is more or less a futile exercise unless you are using Plink or replace the shell entirely with something more robust.

My solution was quite simple, create a O-O VBScript API for running it via CScript that can in turn be called from the NT command line where required.

Buy Adafruit USB Serial RGB Backlight Character LCD Backpack, and other Adafruit components or & help support this site.

 

More Info

This API does what I require it to do. I have implemented all of the main command syntax from the Adafruit documentation (links below). It is classful and self contained. As long as you can create a FileSystemObject and can find the COM Port, you can make use of it.

[Update 25/04/2019] You can now obtain this code directly from Github.

View: AdafruitUsbSerial on GitHub

' AdafruitUsbSerial Application Programming Interface v1.0.4

' © C:Amie | www.c-amie.co.uk 1996 - 2014

' Not for commercial reproduction without the express permission of the author

' No warranty is offered or implied as a result of downloading or using this APIClass AdafruitUsbSerialprivate m_ForReadingprivate m_SCREEN_OFF

private m_SCREEN_ON

private m_AUTO_SCROLL_ON

private m_AUTO_SCROLL_OFF

private m_CLEAR_SCREEN

private m_SET_STARTUP_SPLASH

private m_SET_CURSOR_POSITION

private m_SET_CURSOR_HOME

private m_SET_CURSOR_BACK

private m_SET_CURSOR_FORWARD

private m_SET_UNDERLINE_ON

private m_SET_UNDERLINE_OFF

private m_SET_BLINK_ON

private m_SET_BLINK_OFF

private m_SET_RGB

private m_SET_CONTRAST

private m_SET_BRIGHTNESSprivate m_iPortNumber

private m_byteCharacterLength

private m_bolDebug

private m_bolAutoScroll

private m_bolUnderlineCursor

private m_bolBlinkCursorprivate m_fso private

sub Class_Initialize
m_ForReading = 1
m_SCREEN_OFF = chr(254) & chr(70)
m_SCREEN_ON = chr(254) & chr(66)
m_AUTO_SCROLL_ON = chr(254) & chr(81)
m_AUTO_SCROLL_OFF = chr(254) & chr(82)
m_CLEAR_SCREEN = chr(254) & chr(88)
m_SET_STARTUP_SPLASH = chr(254) & chr(64)
m_SET_CURSOR_POSITION = chr(254) & chr(71)
m_SET_CURSOR_HOME = chr(254) & chr(72)
m_SET_CURSOR_BACK = chr(254) & chr(76)
m_SET_CURSOR_FORWARD = chr(254) & chr(77)
m_SET_UNDERLINE_ON = chr(254) & chr(74)
m_SET_UNDERLINE_OFF = chr(254) & chr(75)
m_SET_BLINK_ON = chr(254) & chr(83)
m_SET_BLINK_OFF = chr(254) & chr(84)
m_SET_RGB = chr(254) & chr(208)
m_SET_CONTRAST = chr(254) & chr(80)
m_SET_BRIGHTNESS = chr(254) & chr(153)

m_iPortNumber = 1
m_byteCharacterLength = 32
m_bolDebug = false
m_bolAutoScroll = true
m_bolUnderlineCursor = false
m_bolBlinkCursor = false

set m_fso = CreateObject("Scripting.FileSystemObject")
end sub

private sub Class_Terminate
set m_fso = nothing
end sub

' PROPERTIES
public property get PortNumber
PortNumber = m_iPortNumber
end property

public property let PortNumber(ByRef iIn)
m_iPortNumber = iIn
end property

public property get CharacterLength
CharacterLength = m_byteCharacterLength
end property

public property let CharacterLength(ByRef byteIn)
m_byteCharacterLength = byteIn
end property

public property get Debug()
Debug = m_bolDebug
end property

public property let Debug(ByRef bolIn)
m_bolDebug = bolIn
end property

public property get AutoScroll()
AutoScroll = m_bolAutoScroll
end property

public property let AutoScroll(ByRef bolIn)
if (bolIn) then
me.write(m_AUTO_SCROLL_ON)
else
me.write(m_AUTO_SCROLL_OFF)
end if
m_bolAutoScroll = bolIn
end property

public property get Underline()
Underline = m_bolUnderlineCursor
end property

public property let Underline(ByRef bolIn)
if (bolIn) then
me.write(m_SET_UNDERLINE_ON)
else
me.write(m_SET_UNDERLINE_OFF)
end if
m_bolUnderlineCursor = bolIn
end property

public property get Blink()
Blink = m_bolBlinkCursor
end property

public property let Blink(ByRef bolIn)
if (bolIn) then
me.write(m_SET_BLINK_ON)
else
me.write(m_SET_BLINK_OFF)
end if
m_bolBlinkCursor = bolIn
end property

' METHODS
public sub clearScreen()
me.write(m_CLEAR_SCREEN)
end sub public sub screenOn()
me.write(m_SCREEN_ON)
end sub

public sub screenOff()
me.write(m_SCREEN_OFF)
end sub

public sub changeSplashScreen(ByVal strIn)
strIn = Left(strIn, m_byteCharacters)
' Force it to be exactly 32 characters by padding
do while (Len(strIn) < m_byteCharacters)
strIn = (strIn & " ")
loop
me.clearScreen()
me.home()
me.write(m_SET_STARTUP_SPLASH)
me.write(strIn)
end sub

public sub backlight(ByRef byteR, ByRef byteG, ByRef byteB)
me.write(m_SET_RGB)
me.write(chr(byteR))
me.write(chr(byteG))
me.write(chr(byteB))
end sub

' Valid Range 0 - 255. Values between 180 and 220 are suggested
public sub contrast(ByRef byteIn)
me.write(m_SET_CONTRAST)
me.write(chr(byteIn))
end sub

' Valid Range 0 - 255.
public sub brightness(ByRef byteIn)
me.write(m_SET_BRIGHTNESS)
me.write(chr(byteIn))
end sub

public sub setCursorPosition(ByRef iX, ByRef iY)
me.write(m_SET_CURSOR_POSITION)
me.write(chr(iX))
me.write(chr(iY))
end sub

public sub home()
me.write(m_SET_CURSOR_HOME)
end sub

public sub back()
me.write(m_SET_CURSOR_BACK)
end sub

public sub goBack(ByRef iIn)
Dim i
for i = 1 to iIn
me.write(m_SET_CURSOR_BACK)
next
end sub

public sub forward()
me.write(m_SET_CURSOR_FORWARD)
end sub

public sub goForward(ByRef iIn)
Dim i
for i = 1 to iIn
me.write(m_SET_CURSOR_FORWARD)
next
end sub

public sub delete()
me.write(m_SET_CURSOR_BACK)
me.write(" ")
me.write(m_SET_CURSOR_BACK)
end sub

public sub write(ByRef strIn)
Dim serialWriter
if (me.Debug) then
wscript.echo strIn
end if
set serialWriter = m_fso.CreateTextFile("COM" & m_iPortNumber & ":",True)
serialWriter.Write(strIn)
serialWriter.Close()
set serialWriter = nothing
end sub

public sub teletype(ByRef strIn, ByRef iDelayMs)
Dim i
Dim iLen
iLen = Len(strIn)
for i = 1 to iLen
me.write(Mid(strIn, i, 1))
WScript.Sleep(iDelayMs)
next
end sub

public function testComPort(ByRef byteNumber)
Dim serialWriter
if (me.Debug) then
wscript.echo "Attempting communications with COM" & byteNumber
end if
On Error Resume Next
set serialWriter = m_fso.CreateTextFile("COM" & byteNumber & ":",True)
serialWriter.Write("Initialising...")
serialWriter.Close()
set serialWriter = nothing
if (err.number = 0) then
testComPort = true
else
testComPort = false
end if
On Error Goto 0
end function

End Class

Copy it into your VBScript project file or into a dedicated class file and include it. Once it is in scope, the example below shows a general usage pattern for the main API.

It is recommended that all projects include and set the first 8 lines shown below, just so that you can ensure that you are tuning your project in the way that you want it. The remainder of the code shows examples of how to use the functions.

As a result of the USB driver allocating COM ports in a fairly dynamic way under Win32, you cannot expect to hard code your COM Port inside the project – particularly if the physical USB port that the backpack is connected to changes. Consequently, you can use testComPort() to attempt to locate the correct port as shown below. The function will terminate on the first port that it finds with an active serial output line available, if you have multiple active serial ports available on your project, the function may find the wrong port.

Finally, Adafruit recommends – at a minimum -adding a 10 millisecond delay between each command, which is not shown below. You should use WScript.Sleep(10) to achieve similar under VBScript. If you don’t, everything shown below with the exception of the executing of the Teletype macro will occur in well under a second.

Dim usbSerial

set usbSerial = new AdafruitUsbSerial

    usbSerial.PortNumber = 3              ' Set to COM3

    usbSerial.Debug = true                ' Inputs will be written back to WScript

    usbSerial.CharacterLength = 32        ' 32 is the default

    usbSerial.AutoScroll = true           ' Enable/Disable Auto Scroll

    usbSerial.Underline = true            ' Enable Cursor Underline

    usbSerial.Blink = true                ' Enable Cursor Blink' Find the first live COM Port if you don't know where it is

Dim iComPort

for iComPort = 1 to 30

    if (usbSerial.testComPort(iComPort)) then

        usbSerial.PortNumber = iComPort

        Exit For

    end if

next' Write Text

usbSerial.write("some text")' Write on both lines

usbSerial.write("line one" & vblf & "line two")' Clear the screen

usbSerial.clearScreen()' Screen Off

usbSerial.screenOff()

' Screen On
usbSerial.screenOn()

' Change the Backlight Colour
call usbSerial.backlight(255, 0, 255) ' Sets the RGB values (Fuchsia in this case)

' Set the screen brightness
usbSerial.brightness(180) ' 0 - 255

' Set the screen contrast
usbSerial.contrast(180) ' 0 - 255

' Set the Cursor Position
usbSerial.home()                  ' Moves to character 1, row 1
usbSerial.back()                  ' Moves the cursor back 1 character
usbSerial.forward()               ' Moves the cursor forward 1 character
usbSerial.goBack(5)               ' Steps the cursor back 5 characters
usbSerial.goForward(6)            ' Progresses the cursor forward 6 characters
usbSerial.setCursorPosition(5,1)  ' Sets the cursor to Character 5 on Row 1
usbSerial.delete()                ' Moves the cursor back 1 and clears the previous character

' Teletype (Macro)
call usbSerial.teletype("this will teletype out", 100) ' Write the text, with a 0.1 second character delay

' Change the Adafruit Splash Screen (Auto truncated/padded to usbSerial.CharacterLength)
usbSerial.changeSplashScreen("This is a splash screen message")

' Clean up and free resources
set usbSerial = nothing

Thanks to a structured API it is as easy as that!

View: Adafruit: Command Reference
View: Adafruit: Sending Text

See Also

View: Adafruit

Buy Adafruit USB Serial RGB Backlight Character LCD Backpack, and other Adafruit components from Amazon & help support this site:

Exploration of which request headers you need, should and cannot set when using MsXml2.XmlHttp, Microsoft.XmlHttp and MsXml2.ServerXmlHttp

System Requirements:

  • Windows NT 4.0 Server SP4+
  • Windows Server 2000
  • Windows Server 2003
  • Windows Server 2008, R2
  • Windows Server 2012, R2
  • Windows 2000 Professional
  • Windows XP
  • Windows Vista
  • Windows 7
  • Windows 8, 8.1
  • IIS 4.0, 5.0, 5.1, 6.0, 7.0, 7.5, 8.0
  • ASP 3.0 (Classic)
  • VBScript

The Problem:

I was browsing around the web earlier looking for inspiration on making PowerShell send asynchronous XmlHttp requests when I came across a block of VBScript examples. In them, I observed that the coder was religiously attempting to set the Content-Length request header, something that when using MsXml I don’t usually do – it’s a different story with PHP.

Equally, I observed that the programmer was using Len() to define the length of the content body for text, but ASP usually operates using an internal UTF-16 encoding to represent strings, thus does it follow that Len() will give the correct value?

So I thought that I would explore the issue to see for my own amusement, what was actually going on.

More Info

Let us take a standard code block to use for our tests and use the services of the good people at httpbin.org for a public message echo system.

Option Explicit
Dim x
Dim strRequest : strRequest = "a=1&b=2&c=3" ' <- 11 charactersset x = CreateObject("MsXml2.XmlHttp")
call x.open("POST", "http://httpbin.org/post", false)
call x.setRequestHeader("Content-Length", 11)
call x.setRequestHeader("Accept-Language", "EN-GB")
call x.setRequestHeader("Connection", "keep-alive")x.send(strRequest)

The above gives us a boiler plate for what we believe the correct header should looklike written in VBScript. When executed, HttpBin responds with:

{
"args": {},
"data": "a=1&b=2&c=3",
"files": {},
"form": {},
"headers": {
"Accept": "*/*",
"Accept-Encoding": "gzip, deflate",
"Accept-Language": "EN-GB",
"Cache-Control": "no-cache",
"Connection": "close",
"Content-Length": "11",
"Host": "httpbin.org",
"User-Agent": "<omitted>",
"X-Request-Id": "<omitted>"
},
"json": null,
"origin": "<ommitted>",
"url": "http://httpbin.org/post"
}

HttpBin provides us with an echo of the header and WireShark provides us with a wire capture of the transport packet being sent between the XmlHttpResponse provider and the HttpBin server. With these two tools we can analyse the header states.

Content-Length

If you take out the line call x.setRequestHeader(“Content-Length”, 11) and do not specify a content-length, both HttpBin and Wireshark’s trace of the connection report Content-Length: 11\r\n, which is correct. So logically, this has been inserted by the XmlHttp parser during the request to .send().

So what happens if we attempt to override it. If we inject call x.setRequestHeader(“Content-Length”, 15), which is 4 characters too long, again both WireShark and HttpBin report

Content-Length: 11\r\n

The same occurs if we under-report the content length, i.e. 10 characters. Therefore it is safe to conclude that MsXml2.XmlHttp’s send() operator handles this for you and any processing of the Len() of the message body before sending is just wasting CPU time, memory and lines of code as it is ultimately an action that will be duplicated.

To further test the theory to see if it is required in down-level versions of MsXml, I repeated the experiment using HttpBin and Wireshark with the following COM objects:

Microsoft.XmlHttp
MsXml2.XmlHttp            <-which is logically v3.0
MsXml2.XmlHttp.3.0
MsXml2.XmlHttp.6.0
MsXml2.ServerXmlHttp      <-which is logically v3.0
MsXml2.ServerXmlHttp.3.0
MsXml2.ServerXmlHttp.6.0

None of them could be coerced to include an incorrectly sized Content-Length and all of them appended the correct 11 character content length on their own when no attempt was made to manually provide it.

We can therefore categorically conclude that with MSXML 3.0 and higher, you do not need to waste time calculating the content length.

A an aside, when dealing with character data, the use of Len() appears to be correct for UTF-8 encoding. LenB() should be used when passing in binary data i.e. ADODB.Stream data, FileSystemObject data etc.

Content-Type

If you do not manually specify a Content-Type header, all MSXML providers appear to transmit POST encoded data as

Content-Type: text/xml; charset="utf-8"\r\n

As we were sending POST data (i.e. a HTML form), this is incorrect as the content-type should be “application/x-www-form-urlencoded; Charset=UTF-8”. Thus is is appropriate and necessary to include the Content-Type header manually as shown below.

call x.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; Charset=UTF-8")

Accept-Language

Accept language was decidedly different depending on which provider you are using. You can safely override Accept-language by manually specifying it using setRequestHeader(“Accept-Language”, “EN-GB”).

Microsoft.XmlHttp         <- NOT SET
MsXml2.XmlHttp.3.0        <- NOT SET
MsXml2.XmlHttp.6.0        <- Derived it from OS i.e. Accept-Language: en-gb\r\n
MsXml2.ServerXmlHttp.3.0  <- Derived it from OS i.e. Accept-Language: en-gb\r\n
MsXml2.ServerXmlHttp.6.0  <- Derived it from OS i.e. Accept-Language: en-gb\r\n

Thus, if you are using the legacy Microsoft.XmlHttp or the client MsXml2.XmlHttp.3.0, it is necessary to manually enter the Accept-Language if of course it is needed.

Connection

All examples set the connection value to Connection: Keep-Alive\r\n when communicating with the HTTP/1.1 protocol. If you need to force the remote server to close the TCP connection immediately after the response has been received, you must manually set Connection: Close\r\n using setRequestHeader(“Connection”, “Close”).

Cache-Control

Cache-control is only set by the client providers and can be added manually to the server providers.

Microsoft.XmlHttp         <- Cache-Control: no-cache\r\n
MsXml2.XmlHttp.3.0        <- Cache-Control: no-cache\r\n
MsXml2.XmlHttp.6.0        <- Cache-Control: no-cache\r\n
MsXml2.ServerXmlHttp.3.0  <- NOT SET
MsXml2.ServerXmlHttp.6.0  <- NOT SET

Accept-Encoding

Accept-encoding is only set by the client providers and can be added manually to the server providers.

Microsoft.XmlHttp         <- Accept-Encoding: gzip, deflate\r\n
MsXml2.XmlHttp.3.0        <- Accept-Encoding: gzip, deflate\r\n
MsXml2.XmlHttp.6.0        <- Accept-Encoding: gzip, deflate\r\n
MsXml2.ServerXmlHttp.3.0  <- NOT SET
MsXml2.ServerXmlHttp.6.0  <- NOT SET

Accept

Accept is set to Accept: */*\r\n by all providers and can be overridden if required.

0x80090020 when attempting to load a .PFX Private Key Certificate into a CAPICOM_MEMORY_STORE using Store.Load() or Certificate.Load() using CAPICOM 2.1.0.2

System Requirements:

  • Windows Server 2008, R2
  • Windows Vista
  • Windows 7
  • Windows 8, 8.1
  • 7.0, 7.5, 8.0
  • ASP 3.0 (Classic)
  • CAPICOM 2.1.0.2

The Problem:

Ah encryption, that most noble of things. One thing that is sure to drive every developer close to the brink on the odd occasion. The one time where clear, concise API documentation should be considered mandatory – and the one place where good API documentation it seems is an obligation itself not to provide. Be it Microsoft, Java, BouncyCastle, PHP it would seem they are all blighted with the same issue.

Attempting to use legacy API on an unsupported platform should seem like an exercise in masochism, however, you know how much I like to avoid using .net whenever I can.

If you attempt to do this

Dim cert
set cert = Server.CreateObject("CAPICOM.Certificate")
call cert.load("c:\myPrivateKey.pfx", "test", CAPICOM_KEY_STORAGE_EXPORTABLE)

or this

const CAPICOM_MEMORY_STORE = 0
const CAPICOM_LOCAL_MACHINE_STORE = 1
const CAPICOM_STORE_OPEN_READ_WRITE = 1
const CAPICOM_KEY_STORAGE_EXPORTABLE = 1Dim store
set store = Server.CreateObject("CAPICOM.Store")
call store.Open(CAPICOM_MEMORY_STORE, "MemoryStore1", CAPICOM_STORE_OPEN_READ_WRITE)
call store.load("c:\myPrivateKey.pfx", "test", CAPICOM_KEY_STORAGE_EXPORTABLE)

you will get back

error '80090020'
/file.asp, line ###

If you send in a .cer file instead of a .pfx, it works without error but doesn’t allow you to access the Private Key.

More Info

Taking the two code samples in order

Dim cert
set cert = Server.CreateObject("CAPICOM.Certificate")
call cert.load("c:\myPrivateKey.pfx", "test", CAPICOM_KEY_STORAGE_EXPORTABLE)

Should you be getting a 0x80070056 error, your password is wrong. If the file doesn’t have a password, only send parameter 1 (which is about to cause you a problem). To resolve the 0x80090020 error while using a CAPICOM_MEMORY_STORE, you need to stop CAPICOM from attempting to insert the certificate as a resource for a user. If the IIS worker process that you are using doesn’t connect to a user account and has no permissions, the default parameter CAPICOM_CURRENT_USER_KEY or 0 will throw 0x80090020.

To change the scope, ensure that you use the fourth parameter and set the value to CAPICOM_LOCAL_MACHINE_KEY.

const CAPICOM_CURRENT_USER_KEY = 0
const CAPICOM_LOCAL_MACHINE_KEY = 1Dim cert
set cert = Server.CreateObject("CAPICOM.Certificate")
call cert.load("c:\myPrivateKey.pfx", "test", CAPICOM_KEY_STORAGE_EXPORTABLE, CAPICOM_LOCAL_MACHINE_KEY)

To resolve the second issue, modify the original code to make use of the now fixed certificate.load() call and import it vie the long route.

const CAPICOM_MEMORY_STORE = 0
const CAPICOM_LOCAL_MACHINE_STORE = 1
const CAPICOM_STORE_OPEN_READ_WRITE = 1
const CAPICOM_KEY_STORAGE_EXPORTABLE = 1Dim cert
Dim store
set store = Server.CreateObject("CAPICOM.Store")
call store.Open(CAPICOM_MEMORY_STORE, "MemoryStore1", CAPICOM_STORE_OPEN_READ_WRITE)set cert = Server.CreateObject("CAPICOM.Certificate")
call cert.load("c:\myPrivateKey.pfx", "test", CAPICOM_KEY_STORAGE_EXPORTABLE, CAPICOM_LOCAL_MACHINE_KEY)

call store.add(cert)

If you receive 0x80070005, you are either getting an Access Denied error to the MEMORY_STORE or you are attempting to import a certificate into the instantiated store which already exists. Similarly, if you receive 0x80070056, your password is wrong.

‘Bug’ in ASP 3.0 Application.Contents iterator causes undesired deletion patterns when Application.Contents.Remove() is called from within a for each / for loop

System Requirements:

  • Windows NT 4.0 Server SP4+
  • Windows Server 2000
  • Windows Server 2003
  • Windows Server 2008, R2
  • Windows Server 2012, R2
  • Windows Server 2016
  • Windows Server 2019
  • Windows 2000 Professional
  • Windows XP
  • Windows Vista
  • Windows 7
  • Windows 8, 8.1
  • windows 10
  • IIS 4.0, 5.0, 5.1, 6.0, 7.0, 7.5, 8.0, 10.0
  • ASP 3.0 (Classic)

The Problem:

I remember, long ago in approximately 2001 – in my less competent days – fighting to make something work and ultimately concluded that it was a hapless endeavour and ultimately went about it in a different way. The task was to clear down all but a small number of elements from the ASP 3.0 Application.Contents object.

What I concluded then, is something that I’ve only just re-remembered now after finally making a determined effort to hunt down a bug in a module on HPC:Factor – which is being used elsewhere – and in which a recent change brought the issue back to light.

There is an iterator issue come bug (depending on your point of view) in the ASP 3.0 Application object.

More Info

We’ll lead by example with this one. After spending an hour or so reacquainting myself with the problem while fixing (read making more robust) the HPC:Factoor class module, a fairly simple process can be used to demonstrate it. Whether or not you see this as a natural feature, or a sincere bug is something that I’ll leave to you. There are always ways around this sort of thing, so I guess that what counts is whether you think it should be fixed in the iterator or by the end user.

Take the following code

Option Explicit
Dim strKey
Application.Contents.RemoveAll()
Application.Contents("one") = "a"
Application.Contents("two") = "b"
Application.Contents("three") = "c"
Application.Contents("four") = "d"
for each strKey in Application.Contents
  Response.Write strKey & " == " & Application.Contents(strKey) & "<br />"
next

It’s obviously going to print out the following

one == a two == b three == c four == d

So what if we now do this:

for each strKey in Application.Contents
  Application.Contents.Remove(strKey)
next
for each strKey in Application.Contents
  Response.Write strKey & " == " & Application.Contents(strKey) & "<br />"
next

Clearly it should print

For dramatic effect, that’s “absolutely nothing being printed”. The application object should be completely empty.

Wrong! It prints:

two == b
four == d

What’s going on is quite simple. The for each iterator being called from the Application.Contents collection is indexed, in other words when items are added or removed they are given a numeric, integer based index in order to aid lookup.

This index becomes stateful as it initially exists at call time for the “for each” provider and its content is copied out to the iterator, By Value (ByVal). It should really be passed out By Reference (ByRef) i.e. via a Pointer.

What this means (using comments to explain the process) is that the following logic occurs:

Option Explicit
Dim strKey
Application.Contents.RemoveAll()            ' Delete all indexes, release pointers to all data
Application.Contents("one") = "a"           ' Create Index 1, Key:"One", Value:"a"
Application.Contents("two") = "b"           ' Create Index 2, Key:"two", Value:"b"
Application.Contents("three") = "c"         ' Create Index 3, Key:"three", Value:"c"
Application.Contents("four") = "d"          ' Create Index 4, Key:"four", Value:"d"
' Application.Contents.Count = 4

for each strKey in Application.Contents     ' Create an iterator of the index [1 - 4]
  ' Iterator Index i = 1
  Application.Contents.Remove(strKey)     ' Remove item at index 1
  ' Index 1 removed, compact index
  ' Index 1, Key:"two", Value:"b"
  ' Index 2, Key:"three", Value:"c"
  ' Index 3, Key:"four", Value:"d"
  ' Application.Contents.Count = 3
  ' Move to NEXT
  ' Iterator Index = 2 (i = (i + 1))
  Application.Contents.Remove(strKey)     ' Remove item at index 2
  ' Index 2 removed, compact index
  ' Index 1, Key:"two", Value:"b"
  ' Index 2, Key:"four", Value:"d"
  ' Application.Contents.Count = 2
  ' Move to NEXT
  ' Iterator Index = 3 (i = (i + 1))
  ' 3 is greater than 2 (the index is > count), exit

The problem is that the Index is being compacted on a successful call to .Remove(). The count of the number of items in Application.Contents is being updated to reflect the correct number of items, but the iterator isn’t being told i = (i – 1) after the successful completion of the Remove() method.

The same thing happens if you use “for” rather than “for each”:

Option Explicit
Dim i
Application.Contents.RemoveAll()
Application.Contents("one") = "a"
Application.Contents("two") = "b"
Application.Contents("three") = "c"
Application.Contents("four") = "d"
for i = 1 to Application.Contents.Count
  Application.Contents.Remove(i)
next

This also results in data still remaining inside the Application Object due to the same error, except here we are directly calling the iteration number ourselves via i so we also get 2 and 4 left in the collection as with calling .Remove() from the “for each”.

If the Application.Contents.Remove method supported a success/failure return type – for example a boolean true for item removed and boolean false for no such item in collection, then the fix would be simple:

for i = 1 to Application.Contents.Count
  if (Application.Contents.Remove(i)) then
    i = (i - i)
  end if
next

Sadly the method doesn’t support a return type.

The Fix

This bug means that there are only two ways to deal with it The first way would be to iterate across the collection, store the Keys in an array and then in a second pass remove all of the items that you want to delete by using an external array.

It does the job and allows you to continue to use keys, but why use two loops when you can use one? In the knowledge that the following is true:

  1. The index is compacting
  2. The iterator is not being reduced by 1 after a successful call to .Remove()

The second and simplest approach to solve the problem is to force the for loop to decrement it for you. In other words, reverse iterate instead of forward iterate through the collection.

Dim i

Application.Contents.RemoveAll()
Application.Contents("one") = 1
Application.Contents("two") = 2
Application.Contents("three") = 3
Application.Contents("four") = 4
for i = Application.Contents.Count to 1 step -1
  Application.Contents.Remove(i)
next

for i = 1 to Application.Contents.Count
  Response.Write Application.Contents.Key(i) & " == " & Application.Contents.Item(i) & "<br />"
next

By going backwards, the index is decremented and so is the external iterator, meaning that they keep in sync with each other.

To adapt this further, if you only want to remove certain items from the collection and want to delete based upon the key, use the following.

Dim i
Application.Contents.RemoveAll()
Application.Contents("one") = 1
Application.Contents("two") = 2
Application.Contents("three") = 3
Application.Contents("four") = 4
for i = Application.Contents.Count to 1 step -1
  if ((Application.Contents.Key(i) = "one") OR (Application.Contents.Key(i) = "three")) then
    Application.Contents.Remove(i)
  end if
next

for i = 1 to Application.Contents.Count
  Response.Write Application.Contents.Key(i) & " == " & Application.Contents.Item(i) & "<br />"
next

Using our example above, the output will correctly be:

two == b
four == d