B4X

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.

B4X

Dim success As Boolean = False

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

Dim scard As ChilkatSCard
scard.Initialize("scard")

'  First establish a context to the PC/SC Resource Manager
success = scard.EstablishContext("user")
If success = False Then
    Log(scard.LastErrorText)
    Return
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 ChilkatJsonObject
json.Initialize
success = scard.FindSmartcards(json)
If success = False Then
    Log(scard.LastErrorText)
    Return
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
Log(json.Emit)
Log(" ")

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

Dim i As Int = 0
Dim count_i As Int = json.SizeOfArray("reader")
Do 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
        Log(name & " has a smart card inserted.")
    Else
        Log(name & " does not have a smart card inserted.")
    End If

    i = i + 1
Loop
Log(" ")

'  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 ChilkatStringTable
stReaders.Initialize
success = scard.ListReaders(stReaders)
If success = False Then
    Log(scard.LastErrorText)
    Return
End If


'  Show the reader names..
Dim numReaders As Int = stReaders.Count
i = 0
Do While i < numReaders
    Log(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 ChilkatJsonObject
json2.Initialize
success = scard.GetStatusChange(30000, stReaders, json2)
If success = False Then
    Log(scard.LastErrorText)
    Return
End If

Log(" ")

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

'  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 Int = json2.IntOf("numChanged")
Log("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 = True Then
        name = json2.StringOf("reader[i].name")
        state = json2.StringOf("reader[i].state")

        Log("Changed: ")
        Log("    reader name: " & name)
        Log("    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")
            Log("    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 = False Then
    Log(scard.LastErrorText)
End If