(VB.NET) PC/SC Wait for Smart Card Status Change (Inserted, Removed from Reader, etc.)

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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 Chilkat.SCard

' First establish a context to the PC/SC Resource Manager
Dim success As Boolean = scard.EstablishContext("user")
If (success = False) Then
    Debug.WriteLine(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 Chilkat.JsonObject
success = scard.FindSmartcards(json)
If (success = False) Then
    Debug.WriteLine(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 = False
Debug.WriteLine(json.Emit())
Debug.WriteLine(" ")

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

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

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

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

    i = i + 1
End While
Debug.WriteLine(" ")

' 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 Chilkat.StringTable
success = scard.ListReaders(stReaders)
If (success = False) Then
    Debug.WriteLine(scard.LastErrorText)
    Exit Sub
End If


' Show the reader names..
Dim numReaders As Integer = stReaders.Count
i = 0
While i < numReaders
    Debug.WriteLine(i & ": " & stReaders.StringAt(i))
    i = i + 1
End While

' 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 Chilkat.JsonObject
success = scard.GetStatusChange(30000,stReaders,json2)
If (success = False) Then
    Debug.WriteLine(scard.LastErrorText)
    Exit Sub
End If

Debug.WriteLine(" ")

' Let's see what happened...
json2.EmitCompact = False
Debug.WriteLine(json2.Emit())
Debug.WriteLine(" ")

' 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 Boolean
Dim state As String
Dim atr As String

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

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

        Debug.WriteLine("Changed: ")
        Debug.WriteLine("    reader name: " & name)
        Debug.WriteLine("    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") = True) Then
            atr = json2.StringOf("reader[i].atr")
            Debug.WriteLine("    ATR of card inserted into this reader: " & atr)
        End If

    End If

    i = i + 1
End While

' 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 = False) Then
    Debug.WriteLine(scard.LastErrorText)
End If