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

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Demonstrates how to start an asynchronous Chilkat task to wait for a status change, such as for a smart card to be inserted into a reader, or removed from a reader. After starting the background task, the code loops to check on the status of your task.

Note: Instead of writing a loop to wait for the status change, your application might periodically check the task status via a timer event or something similar. The purpose of this example is to show (1) how to start the async task, and (2) how to periodically check the status of the task.

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

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LOCAL loScard
LOCAL lnSuccess
LOCAL loStReaders
LOCAL loJson
LOCAL loTask

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.SCard')
loScard = CreateObject('Chilkat.SCard')

* First establish a context to the PC/SC Resource Manager
lnSuccess = loScard.EstablishContext("user")
IF (lnSuccess = 0) THEN
    ? loScard.LastErrorText
    RELEASE loScard
    CANCEL
ENDIF

* Get the list of all readers.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringTable')
loStReaders = CreateObject('Chilkat.StringTable')
lnSuccess = loScard.ListReaders(loStReaders)
IF (lnSuccess = 0) THEN
    ? loScard.LastErrorText
    RELEASE loScard
    RELEASE loStReaders
    CANCEL
ENDIF

* Create a Chilkat task to wait for a max of 1 hour (3600 seconds, or 3600000 milliseconds) for any smart card reader status change.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJson = CreateObject('Chilkat.JsonObject')
loTask = loScard.GetStatusChangeAsync(3600000,loStReaders,loJson)
IF (loScard.LastMethodSuccess = 0) THEN
    ? loScard.LastErrorText
    RELEASE loScard
    RELEASE loStReaders
    RELEASE loJson
    CANCEL
ENDIF

* Start the task in a background thread.
lnSuccess = loTask.Run()
IF (NOT lnSuccess) THEN
    ? loTask.LastErrorText
ENDIF

* Loop until the task is finished, which happens when any reader's status changes.
* Instead of looping here, your application could periodically check on the task status in some other way,
* such as in a periodic timer event..
DO WHILE loTask.Finished <> 1

    * Sleep 100 ms.  
    loTask.SleepMs(100)
ENDDO

* When we call GetStatusChangeAsync, what's really happening is that GetStatusChange is being called in a background thread.
* It returns a boolean (success/failure).  Therefore, we call task.GetResultBool to get the boolean returned by GetStatusChange
* in the background thread.
lnSuccess = loTask.GetResultBool()
IF (lnSuccess = 0) THEN
    * The call to GetStatusChange in the background thread failed.  Let's find out why by getting the LastErrorText
    * for the background synchronous call.
    ? loTask.ResultErrorText
ENDIF

RELEASE loTask

* If the background call to GetStatusChange succeeded, then the result was placed in the last arg,
* which was our variable named "json".
IF (lnSuccess = 0) THEN
    RELEASE loScard
    RELEASE loStReaders
    RELEASE loJson
    CANCEL
ENDIF

* Let's see what happened...
loJson.EmitCompact = 0
? loJson.Emit()
? " "

* See the Wait for Smart Card Insertion/Removal Example for details about parsing the returned JSON.

* Applications should always release the context when finished.
lnSuccess = loScard.ReleaseContext()
IF (lnSuccess = 0) THEN
    ? loScard.LastErrorText
ENDIF

* Note: It may be necessary to call FinalizeThreadPool in some programming environments just before your program exits.
* (Not after every async function call, but only before program exit.)
* See Call FinalizeThreadPool before program exit

RELEASE loScard
RELEASE loStReaders
RELEASE loJson