(Visual Basic 6.0) PC/SC Wait for Smart Card Status Change (Inserted, Removed from Reader, etc.)

See more SCard Examples

Demonstrates how to synchronously wait for a status change, such as for a smart card to be inserted into a reader, or removed from a reader.

Note: This functionality was introduced in Chilkat v9.5.0.87.

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' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim scard As New ChilkatSCard

' First establish a context to the PC/SC Resource Manager
Dim success As Long
success = scard.EstablishContext("user")
If (success = 0) Then
    Debug.Print scard.LastErrorText
    Exit Sub
End If

' First we'll examine the state of all connected readers to see which have smartcards already inserted..
' Get JSON containing information about the smartcards currently inserted into readers.
' This also includes information about USB security tokens.
Dim json As New ChilkatJsonObject
success = scard.FindSmartcards(json)
If (success = 0) Then
    Debug.Print scard.LastErrorText
    Exit Sub
End If

' When writing this example, I have 3 smart card readers plugged into my system.
' One of them has a smart card inserted.
' Here's the JSON returned by FindSmartcards...

' {
'   "reader": [
'     {
'       "name": "Alcor Micro USB Smart Card Reader 0",
'       "state": "empty"
'     },
'     {
'       "name": "Generic Smart Card Reader Interface 0",
'       "state": "present",
'       "vendorName": "Generic",
'       "serialNumber": "3230303730383138303030303030303030",
'       "systemName": "Generic Smart Card Reader Interface 0",
'       "card": {
'         "atr": "3BFC180000813180459067464A00641606F2727E00E0",
'         "windows": {
'           "miniDriver": "tagliov70px.dll",
'           "cryptoProvider": "Microsoft Base Smart Card Crypto Provider",
'           "keyStorageProvider": "Microsoft Smart Card Key Storage Provider"
'         }
'       }
'     },
'     {
'       "name": "SCM Microsystems Inc. SCR33x USB Smart Card Reader 0",
'       "state": "empty"
'     }
'   ]
' }

json.EmitCompact = 0
Debug.Print json.Emit()
Debug.Print " "

' We can iterate over the JSON to find the readers with a smart card already inserted..
Dim name As String
Dim sbState As New ChilkatStringBuilder

Dim i As Long
i = 0
Dim count_i As Long
count_i = json.SizeOfArray("reader")
Do While i < count_i
    json.I = i
    name = json.StringOf("reader[i].name")

    sbState.Clear 
    success = json.StringOfSb("reader[i].state",sbState)

    If (sbState.Contains("present",1) = 1) Then
        Debug.Print name & " has a smart card inserted."
    Else
        Debug.Print name & " does not have a smart card inserted."
    End If

    i = i + 1
Loop
Debug.Print " "

' Now let's begin the code to wait for a change (where a smart card gets inserted or removed)

' Get the list of all readers.
Dim stReaders As New ChilkatStringTable
success = scard.ListReaders(stReaders)
If (success = 0) Then
    Debug.Print scard.LastErrorText
    Exit Sub
End If

' Show the reader names..
Dim numReaders As Long
numReaders = stReaders.Count
i = 0
Do While i < numReaders
    Debug.Print i & ": " & stReaders.StringAt(i)
    i = i + 1
Loop

' Sample output from the above loop.
' 0: Alcor Micro USB Smart Card Reader 0
' 1: Generic Smart Card Reader Interface 0
' 2: SCM Microsystems Inc. SCR33x USB Smart Card Reader 0
' 

' Synchronously wait 30 seconds for a card to be inserted or removed from any of the above readers.
Dim json2 As New ChilkatJsonObject
success = scard.GetStatusChange(30000,stReaders,json2)
If (success = 0) Then
    Debug.Print scard.LastErrorText
    Exit Sub
End If

Debug.Print " "

' Let's see what happened...
json2.EmitCompact = 0
Debug.Print json2.Emit()
Debug.Print " "

' This is what json2 contains.
' A card was inserted into the reader named "SCM Microsystems Inc. SCR33x USB Smart Card Reader 0"
' The "numChanged" indicates that one reader's status changed.  
' The "changed":true indicates the reader that changed.   The state is now "present".

' {
'   "numChanged": 1,
'   "reader": [
'     {
'       "name": "Alcor Micro USB Smart Card Reader 0",
'       "changed": false,
'       "state": "empty"
'     },
'     {
'       "name": "Generic Smart Card Reader Interface 0",
'       "changed": false,
'       "state": "present",
'       "atr": "3BFC180000813180459067464A00641606F2727E00E0"
'     },
'     {
'       "name": "SCM Microsystems Inc. SCR33x USB Smart Card Reader 0",
'       "changed": true,
'       "state": "present",
'       "atr": "3BDF96FF8131FE455A018048494443313158587300011B09"
'     }
'   ]
' }

' Find the reader that changed...
Dim changed As Long
Dim state As String
Dim atr As String

Dim numChanged As Long
numChanged = json2.IntOf("numChanged")
Debug.Print "number of readers with a changed state: " & numChanged

i = 0
count_i = json2.SizeOfArray("reader")
Do While i < count_i
    json2.I = i
    changed = json2.BoolOf("reader[i].changed")
    If (changed = 1) Then
        name = json2.StringOf("reader[i].name")
        state = json2.StringOf("reader[i].state")

        Debug.Print "Changed: "
        Debug.Print "    reader name: " & name
        Debug.Print "    new state: " & state

        ' If a card is now in this reader, we should have the ATR of the card..
        If (json2.HasMember("reader[i].atr") = 1) Then
            atr = json2.StringOf("reader[i].atr")
            Debug.Print "    ATR of card inserted into this reader: " & atr
        End If

    End If

    i = i + 1
Loop

' The output from the above loop:

' number of readers with a changed state: 1
' Changed: 
'     reader name: SCM Microsystems Inc. SCR33x USB Smart Card Reader 0
'     new state: present
'     ATR of card inserted into this reader: 3BDF96FF8131FE455A018048494443313158587300011B09

' Applications should always release the context when finished.
success = scard.ReleaseContext()
If (success = 0) Then
    Debug.Print scard.LastErrorText
End If