--- product: Chilkat product_version: 11.7.0 language: pascal language_label: Lazarus Pascal class: SCard license: bundle deprecated: false reference_html: https://www.chilkatsoft.com/refdoc/pascal_SCardRef.html --- # Chilkat SCard — Lazarus Pascal — v11.7.0 > Chilkat 11.7.0 · language=pascal · class=SCard > Other versions: replace `11.7.0` in this URL. Other languages: `https://www.chilkatsoft.com/ai-docs/v/11.7.0//classes/SCard.md`. > Language-wide rules (install, unlock, error model, strings/bytes): `https://www.chilkatsoft.com/ai-docs/v/11.7.0/pascal/guide.md`. ## Purpose **Communicate directly with smart card readers and cards through PC/SC.** `Chilkat.SCard` is the low-level PC/SC smart card interface for applications that need direct reader and card communication. It supports reader discovery, reader connection, card status checking, APDU transmission, reader-control commands, status-change monitoring, transactions, and diagnostic access to underlying PC/SC errors. Use this class when the application needs APDU-level control rather than a higher-level certificate, minidriver, or PKCS#11 abstraction. **Reader discovery** Enumerate available PC/SC smart card readers and identify the reader the application should use. **Connect to cards** Connect to a reader/card, check card presence and status, and manage the active PC/SC connection. **Transmit APDUs** Send APDU commands directly to the card and receive the raw response bytes and status words. **Reader-control commands** Issue lower-level reader control commands when supported by the reader driver and PC/SC environment. **Status monitoring** Monitor reader or card status changes so applications can detect card insertion, removal, or state changes. **Transactions and diagnostics** Use PC/SC transactions for coordinated card access and inspect detailed error information when reader or card operations fail. **Common pattern:** Establish the PC/SC context, list readers, connect to the selected reader, check card status, transmit APDU commands, process the response bytes, and disconnect when finished. Use `Chilkat.SCard` for direct PC/SC reader and APDU-level work; use `Chilkat.ScMinidriver` for card-minidriver certificate and key-container operations, and `Chilkat.Pkcs11` for PKCS#11 token or HSM sessions. For an extended overview, see [SCard Class Overview](https://www.chilkatsoft.com/scard_class_overview.asp). ## Object creation, unlocking and error handling **Create / Free** ```pascal uses Chilkat.SCard; var obj: TSCard; begin obj := TSCard.Create; try if not obj.IsValid then raise Exception.Create('Failed to create a TSCard instance.'); // ... use obj ... finally obj.Free; end; end; ``` `constructor Create;` Allocates the underlying CkSCard object and returns a new TSCard instance. Simply adding **Chilkat.SCard** to the unit's `uses` clause is enough to locate and bind to the Chilkat shared library (DLL / .so / .dylib) at runtime — no separate load step is required. Check `obj.IsValid` after calling `Create`; it is `False` if the underlying library could not be found/loaded or the object could not be allocated (for example, when unlicensed). `destructor Destroy; override;` Every TSCard created by calling `Create` should eventually be released by calling `.Free` (inherited from `TObject`). The destructor automatically disposes the underlying CkSCard handle. A native (unmanaged) memory leak occurs if the object is never freed. Call `Global.UnlockBundle` once at the start of the program, before using this or any other Chilkat class. Any string unlocks a fully functional 30-day trial; a purchased unlock code is used in production. See `guide.md` for the exact code in Lazarus Pascal. ## Members common to every Chilkat class Documented once per language in `common-members.md`; listed here so this page is self-contained. | Property | Signature | Access | Meaning | |---|---|---|---| | `DebugLogFilePath` | `property DebugLogFilePath: string read GetDebugLogFilePath write SetDebugLogFilePath;` | read/write | If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. | | `LastErrorHtml` | `property LastErrorHtml: string read GetLastErrorHtml;` | read-only | Provides HTML-formatted information about the last called method or property. | | `LastErrorText` | `property LastErrorText: string read GetLastErrorText;` | read-only | Provides plain text information about the last called method or property. | | `LastErrorXml` | `property LastErrorXml: string read GetLastErrorXml;` | read-only | Provides XML-formatted information about the last called method or property. | | `LastMethodSuccess` | `property LastMethodSuccess: Boolean read GetLastMethodSuccess write SetLastMethodSuccess;` | read/write | Indicates the success or failure of the most recent method call: `True` means success, `False` means failure. | | `VerboseLogging` | `property VerboseLogging: Boolean read GetVerboseLogging write SetVerboseLogging;` | read/write | If set to `True`, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. | | `Version` | `property Version: string read GetVersion;` | read-only | Version of the component/library, such as "10.1.0" | ## Member index | Member | Kind | Signature | |---|---|---| | `ActiveProtocol` | property, read-only | `property ActiveProtocol: string read GetActiveProtocol;` | | `CardAtr` | property, read-only | `property CardAtr: string read GetCardAtr;` | | `ConnectedReader` | property, read-only | `property ConnectedReader: string read GetConnectedReader;` | | `Context` | property, read-only | `property Context: string read GetContext;` | | `PcscLibPath` | property, read/write | `property PcscLibPath: string read GetPcscLibPath write SetPcscLibPath;` | | `ReaderStatus` | property, read-only | `property ReaderStatus: string read GetReaderStatus;` | | `ScardError` | property, read-only | `property ScardError: string read GetScardError;` | | `BeginTransaction` | method | `function BeginTransaction: Boolean;` | | `CheckStatus` | method | `function CheckStatus: Boolean;` | | `Connect` | method | `function Connect(const reader: string;     const shareMode: string;     const preferredProtocol: string): Boolean;` | | `Disconnect` | method | `function Disconnect(const disposition: string): Boolean;` | | `EndTransaction` | method | `function EndTransaction(const disposition: string): Boolean;` | | `EstablishContext` | method | `function EstablishContext(const scope: string): Boolean;` | | `FindSmartcards` | method | `// json is a TJsonObject object. function FindSmartcards(json: TChilkatBase): Boolean;` | | `GetAttrib` | method | `// bd is a TBinData object. function GetAttrib(const attr: string;     bd: TChilkatBase): Boolean;` | | `GetAttribStr` | method | `function GetAttribStr(const attr: string): string;` | | `GetAttribUint` | method | `function GetAttribUint(const attr: string): LongWord;` | | `GetStatusChange` | method | `// stReaderNames is a TStringTable object. // json is a TJsonObject object. function GetStatusChange(maxWaitMs: Integer;     stReaderNames: TChilkatBase;     json: TChilkatBase): Boolean;` | | `GetStatusChangeCancel` | method | `function GetStatusChangeCancel: Boolean;` | | `ListReaderGroups` | method | `// readerGroups is a TStringTable object. function ListReaderGroups(readerGroups: TChilkatBase): Boolean;` | | `ListReaders` | method | `// st is a TStringTable object. function ListReaders(st: TChilkatBase): Boolean;` | | `Reconnect` | method | `function Reconnect(const shareMode: string;     const preferredProtocol: string;     const action: string): Boolean;` | | `ReleaseContext` | method | `function ReleaseContext: Boolean;` | | `SendControl` | method | `// bdSend is a TBinData object. // bdRecv is a TBinData object. function SendControl(controlCode: LongWord;     bdSend: TChilkatBase;     bdRecv: TChilkatBase): Boolean;` | | `SendControlHex` | method | `// bdRecv is a TBinData object. function SendControlHex(controlCode: LongWord;     const sendData: string;     bdRecv: TChilkatBase): Boolean;` | | `Transmit` | method | `// bdSend is a TBinData object. // bdRecv is a TBinData object. function Transmit(const protocolName: string;     bdSend: TChilkatBase;     bdRecv: TChilkatBase;     maxRecvLen: Integer): Boolean;` | | `TransmitHex` | method | `// bdRecv is a TBinData object. function TransmitHex(const protocolName: string;     const apduHex: string;     bdRecv: TChilkatBase;     maxRecvLen: Integer): Boolean;` | ## Properties ### SCard.ActiveProtocol `Chilkat 11.7.0 · pascal · SCard · ActiveProtocol · property · read-only · since 9.50.87` ```pascal property ActiveProtocol: string read GetActiveProtocol; ``` The name of the active protocol if connected smart card reader, or an empty string if not connected. Possible values are `T0`, `T1`, `raw`, `undefined`, or if not connected to a reader. ### SCard.CardAtr `Chilkat 11.7.0 · pascal · SCard · CardAtr · property · read-only · since 9.50.87` ```pascal property CardAtr: string read GetCardAtr; ``` This is the Current ATR of a card in the connected reader. ### SCard.ConnectedReader `Chilkat 11.7.0 · pascal · SCard · ConnectedReader · property · read-only · since 9.50.87` ```pascal property ConnectedReader: string read GetConnectedReader; ``` The name of the currently connected smart card reader, or an empty string if not connected. ### SCard.Context `Chilkat 11.7.0 · pascal · SCard · Context · property · read-only · since 9.50.87` ```pascal property Context: string read GetContext; ``` Contains the string `user` or `system` if this object has established a context (by calling EstablishContext). Contains the empty string if no context is established. ### SCard.PcscLibPath `Chilkat 11.7.0 · pascal · SCard · PcscLibPath · property · read/write · since 9.50.87` ```pascal property PcscLibPath: string read GetPcscLibPath write SetPcscLibPath; ``` For Linux systems only. Specifies the full path of the libpcsclite.so shared lib. This property should only be used if the libpcsclite.so is in a non-standard location or if Chilkat cannot automatically located it. ### SCard.ReaderStatus `Chilkat 11.7.0 · pascal · SCard · ReaderStatus · property · read-only · since 9.50.87` ```pascal property ReaderStatus: string read GetReaderStatus; ``` The current status of the connected reader. Possible values are: - `absent` - There is no card in the reader. - `present` - There is a card in the reader, but it has not been moved into position for use. - `swallowed` - There is a card in the reader in position for use. The card is not powered. - `powered` - Power is being provided to the card, but the reader driver is unaware of the mode of the card. - `negotiable` - The card has been reset and is awaiting PTS negotiation. - `specific` - The card has been reset and specific communication protocols have been established. ### SCard.ScardError `Chilkat 11.7.0 · pascal · SCard · ScardError · property · read-only · since 9.50.87` ```pascal property ScardError: string read GetScardError; ``` The last error returned by an underlying PC/SC function. Can be one of the following: - `SCARD_W_REMOVED_CARD` - The smart card has been removed, so that further communication is not possible. - `SCARD_W_RESET_CARD` - The smart card has been reset, so any shared state information is invalid. ... ## Methods ### SCard.BeginTransaction `Chilkat 11.7.0 · pascal · SCard · BeginTransaction · method · since 9.50.87` ```pascal function BeginTransaction: Boolean; ``` Establishes a temporary exclusive access mode for doing a series of commands in a transaction. Returns True for success, False for failure. ### SCard.CheckStatus `Chilkat 11.7.0 · pascal · SCard · CheckStatus · method · since 9.50.87` ```pascal function CheckStatus: Boolean; ``` Check the current status of the currently connected reader. Calling this method updates the ReaderStatus, ActiveProtocol, and CardAtr properties. If this method returns `False`, none of the properties are updated. Returns True for success, False for failure. ### SCard.Connect `Chilkat 11.7.0 · pascal · SCard · Connect · method · since 9.50.87` ```pascal function Connect(const reader: string;     const shareMode: string;     const preferredProtocol: string): Boolean; ``` Establish a connection to a reader. The `reader` is the name of a reader returned from ListReaders. The `shareMode` can be `shared`, `exclusive`, or `direct`. The `preferredProtocol` can be `0` (valid only if the shareMode = `direct`), `T0`, `T1`, `raw`, or `no_preference`. (No preference is effectively T0 or T1.) If successful, the state of this object instance is that it's connected to the reader. Returns True for success, False for failure. ### SCard.Disconnect `Chilkat 11.7.0 · pascal · SCard · Disconnect · method · since 9.50.87` ```pascal function Disconnect(const disposition: string): Boolean; ``` Terminates a connection with a reader. The `disposition` can be one of the following values: - `leave`: Do nothing. - `reset`: Reset the card (warm reset). - `unpower`: Power down the card (cold reset). - `eject`: Eject the card. Returns True for success, False for failure. ### SCard.EndTransaction `Chilkat 11.7.0 · pascal · SCard · EndTransaction · method · since 9.50.87` ```pascal function EndTransaction(const disposition: string): Boolean; ``` Ends a previously begun transaction. The `disposition` is the action to be taken on the reader, and can be `leave` which is to do nothing, `reset`, `unpower`, or `eject`. Returns True for success, False for failure. ### SCard.EstablishContext `Chilkat 11.7.0 · pascal · SCard · EstablishContext · method · since 9.5.0.87` ```pascal function EstablishContext(const scope: string): Boolean; ``` Creates an Application Context to the PC/SC Resource Manager. This must be the first WinSCard function called in a PC/SC application. The `scope` can be `user` or `system`. After calling, this object will have context and all other methods will use the established context. The `Context` property will hold the value `user` or `system` if context was established, or will be empty if no context was established. Returns True for success, False for failure. ### SCard.FindSmartcards `Chilkat 11.7.0 · pascal · SCard · FindSmartcards · method · since 9.50.87` ```pascal // json is a TJsonObject object. function FindSmartcards(json: TChilkatBase): Boolean; ``` Returns JSON containing information about the smartcards currently inserted into readers. Returns True for success, False for failure. ### SCard.GetAttrib `Chilkat 11.7.0 · pascal · SCard · GetAttrib · method · since 9.50.87` ```pascal // bd is a TBinData object. function GetAttrib(const attr: string;     bd: TChilkatBase): Boolean; ``` Get an attribute from the IFD Handler (reader driver). The `attr` can be one of the following: - `ASYNC_PROTOCOL_TYPES` - `ATR_STRING` - `CHANNEL_ID` - `CHARACTERISTICS` - `CURRENT_BWT` - `CURRENT_CLK` - `CURRENT_CWT` - `CURRENT_D` - `CURRENT_EBC_ENCODING` - `CURRENT_F` - `CURRENT_IFSC` - `CURRENT_IFSD` - `CURRENT_IO_STATE` - `CURRENT_N` - `CURRENT_PROTOCOL_TYPE` - `CURRENT_W` - `DEFAULT_CLK` - `DEFAULT_DATA_RATE` - `DEVICE_FRIENDLY_NAME` - `DEVICE_IN_USE` - `DEVICE_SYSTEM_NAME` - `DEVICE_UNIT` - `ESC_AUTHREQUEST` - `ESC_CANCEL` - `ESC_RESET` - `EXTENDED_BWT` - `ICC_INTERFACE_STATUS` - `ICC_PRESENCE` - `ICC_TYPE_PER_ATR` - `MAX_CLK` - `MAX_DATA_RATE` - `MAX_IFSD` - `MAXINPUT` - `POWER_MGMT_SUPPORT` - `SUPRESS_T1_IFS_REQUEST` - `SYNC_PROTOCOL_TYPES` - `USER_AUTH_INPUT_DEVICE` - `USER_TO_CARD_AUTH_DEVICE` - `VENDOR_IFD_SERIAL_NO` - `VENDOR_IFD_TYPE` - `VENDOR_IFD_VERSION` - `VENDOR_NAME` The attribute data is returned in `bd`. Returns True for success, False for failure. ### SCard.GetAttribStr `Chilkat 11.7.0 · pascal · SCard · GetAttribStr · method · since 9.50.87` ```pascal function GetAttribStr(const attr: string): string; ``` Get a string typed attribute from the IFD Handler (reader driver). The `attr` can be one of the following, but should be limited to the particular attributes that return string values. - `ASYNC_PROTOCOL_TYPES` - `ATR_STRING` - `CHANNEL_ID` - `CHARACTERISTICS` - `CURRENT_BWT` - `CURRENT_CLK` - `CURRENT_CWT` - `CURRENT_D` - `CURRENT_EBC_ENCODING` - `CURRENT_F` - `CURRENT_IFSC` - `CURRENT_IFSD` - `CURRENT_IO_STATE` - `CURRENT_N` - `CURRENT_PROTOCOL_TYPE` - `CURRENT_W` - `DEFAULT_CLK` - `DEFAULT_DATA_RATE` - `DEVICE_FRIENDLY_NAME` - `DEVICE_IN_USE` - `DEVICE_SYSTEM_NAME` - `DEVICE_UNIT` - `ESC_AUTHREQUEST` - `ESC_CANCEL` - `ESC_RESET` - `EXTENDED_BWT` - `ICC_INTERFACE_STATUS` - `ICC_PRESENCE` - `ICC_TYPE_PER_ATR` - `MAX_CLK` - `MAX_DATA_RATE` - `MAX_IFSD` - `MAXINPUT` - `POWER_MGMT_SUPPORT` - `SUPRESS_T1_IFS_REQUEST` - `SYNC_PROTOCOL_TYPES` - `USER_AUTH_INPUT_DEVICE` - `USER_TO_CARD_AUTH_DEVICE` - `VENDOR_IFD_SERIAL_NO` - `VENDOR_IFD_TYPE` - `VENDOR_IFD_VERSION` - `VENDOR_NAME` Returns True for success, False for failure. ### SCard.GetAttribUint `Chilkat 11.7.0 · pascal · SCard · GetAttribUint · method · since 9.50.87` ```pascal function GetAttribUint(const attr: string): LongWord; ``` Get an unsigned integer typed attribute from the IFD Handler (reader driver). The `attr` can be one of the following, but should be limited to the particular attributes that return unsigned integer values. - `ASYNC_PROTOCOL_TYPES` - `ATR_STRING` - `CHANNEL_ID` - `CHARACTERISTICS` - `CURRENT_BWT` - `CURRENT_CLK` - `CURRENT_CWT` - `CURRENT_D` - `CURRENT_EBC_ENCODING` - `CURRENT_F` - `CURRENT_IFSC` - `CURRENT_IFSD` - `CURRENT_IO_STATE` - `CURRENT_N` - `CURRENT_PROTOCOL_TYPE` - `CURRENT_W` - `DEFAULT_CLK` - `DEFAULT_DATA_RATE` - `DEVICE_FRIENDLY_NAME` - `DEVICE_IN_USE` - `DEVICE_SYSTEM_NAME` - `DEVICE_UNIT` - `ESC_AUTHREQUEST` - `ESC_CANCEL` - `ESC_RESET` - `EXTENDED_BWT` - `ICC_INTERFACE_STATUS` - `ICC_PRESENCE` - `ICC_TYPE_PER_ATR` - `MAX_CLK` - `MAX_DATA_RATE` - `MAX_IFSD` - `MAXINPUT` - `POWER_MGMT_SUPPORT` - `SUPRESS_T1_IFS_REQUEST` - `SYNC_PROTOCOL_TYPES` - `USER_AUTH_INPUT_DEVICE` - `USER_TO_CARD_AUTH_DEVICE` - `VENDOR_IFD_SERIAL_NO` - `VENDOR_IFD_TYPE` - `VENDOR_IFD_VERSION` - `VENDOR_NAME` Returns 0xFFFFFFFF on failure. ### SCard.GetStatusChange `Chilkat 11.7.0 · pascal · SCard · GetStatusChange · method · since 9.50.87` ```pascal // stReaderNames is a TStringTable object. // json is a TJsonObject object. function GetStatusChange(maxWaitMs: Integer;     stReaderNames: TChilkatBase;     json: TChilkatBase): Boolean; ``` Blocks execution until the current availability of the cards in a specific set of readers changes. This function receives a list of reader names in `stReaderNames`. It then blocks waiting for a change in state to occur for a maximum blocking time of `maxWaitMs` (in milliseconds) or forever if 0 is used. Information about the current reader states and which reader(s) changed is returned in `json`. See the example below for more information. To wait for a reader event (reader added or removed) you may use the special reader name `\\?PnP?\Notification`. To cancel the ongoing call, call Cancel(). The `stReaderNames` contains the reader names to check. The `json` is empty on input, and if the call returns success contains information about the state (after the event change) of each reader. Returns True for success, False for failure. ### SCard.GetStatusChangeCancel `Chilkat 11.7.0 · pascal · SCard · GetStatusChangeCancel · method · since 9.50.87` ```pascal function GetStatusChangeCancel: Boolean; ``` Cancels an ongoing GetStatusChange method call. This would be called from a separate thread in your application if GetStatusChange was called synchronously. Returns True for success, False for failure. ### SCard.ListReaderGroups `Chilkat 11.7.0 · pascal · SCard · ListReaderGroups · method · since 9.50.87` ```pascal // readerGroups is a TStringTable object. function ListReaderGroups(readerGroups: TChilkatBase): Boolean; ``` Returns a list of currently available reader groups on the system. The reader groups are returned in `readerGroups`. Returns True for success, False for failure. ### SCard.ListReaders `Chilkat 11.7.0 · pascal · SCard · ListReaders · method · since 9.50.87` ```pascal // st is a TStringTable object. function ListReaders(st: TChilkatBase): Boolean; ``` Returns a list of currently available readers on the system. Returns True for success, False for failure. ### SCard.Reconnect `Chilkat 11.7.0 · pascal · SCard · Reconnect · method · since 9.50.87` ```pascal function Reconnect(const shareMode: string;     const preferredProtocol: string;     const action: string): Boolean; ``` Reestablishes a connection to a reader that was previously connected to using Connect(). In a multi application environment it is possible for an application to reset the card in shared mode. When this occurs any other application trying to access certain commands will be returned the value SCARD_W_RESET_CARD. When this occurs Reconnect() must be called in order to acknowledge that the card was reset and allow it to change its state accordingly. The `shareMode` can be `shared`, `exclusive`, or `direct`. The `preferredProtocol` can be `0` (valid only if the shareMode = `direct`), `T0`, `T1`, `raw`, or `no_preference`. (No preference is effectively T0 or T1.) The `action` is the desired action taken on the card/reader. It can be `leave`, `reset`, `unpower`, or `eject`. If successful, the state of this object instance is that it's connected to the reader. Returns True for success, False for failure. ### SCard.ReleaseContext `Chilkat 11.7.0 · pascal · SCard · ReleaseContext · method · since 9.50.87` ```pascal function ReleaseContext: Boolean; ``` Destroys a communication context to the PC/SC Resource Manager. This must be the last function called in a PC/SC application. Returns True for success, False for failure. ### SCard.SendControl `Chilkat 11.7.0 · pascal · SCard · SendControl · method · since 9.50.87` ```pascal // bdSend is a TBinData object. // bdRecv is a TBinData object. function SendControl(controlCode: LongWord;     bdSend: TChilkatBase;     bdRecv: TChilkatBase): Boolean; ``` Sends a command directly to the IFD Handler (reader driver) to be processed by the reader. This is useful for creating client side reader drivers for functions like PIN pads, biometrics, or other extensions to the normal smart card reader that are not normally handled by PC/SC. The command data is sent in `bdSend`. The response is written to `bdRecv`. Returns True for success, False for failure. ### SCard.SendControlHex `Chilkat 11.7.0 · pascal · SCard · SendControlHex · method · since 9.50.87` ```pascal // bdRecv is a TBinData object. function SendControlHex(controlCode: LongWord;     const sendData: string;     bdRecv: TChilkatBase): Boolean; ``` Sends a command directly to the IFD Handler (reader driver) to be processed by the reader. This is useful for creating client side reader drivers for functions like PIN pads, biometrics, or other extensions to the normal smart card reader that are not normally handled by PC/SC. The command data is provided as a hex string in `sendData`. The response is written to `bdRecv`. Returns True for success, False for failure. ### SCard.Transmit `Chilkat 11.7.0 · pascal · SCard · Transmit · method · since 9.50.87` ```pascal // bdSend is a TBinData object. // bdRecv is a TBinData object. function Transmit(const protocolName: string;     bdSend: TChilkatBase;     bdRecv: TChilkatBase;     maxRecvLen: Integer): Boolean; ``` Sends an APDU to the smart card contained in the currently connected reader. The `protocolName` can be `T0`, `T1`, or `raw`. The APDU to be sent is contained in `bdSend`. The response from the card is contained in `bdRecv`. The `maxRecvLen` is the maximum response size (in bytes) willing to be accepted. Returns True for success, False for failure. ### SCard.TransmitHex `Chilkat 11.7.0 · pascal · SCard · TransmitHex · method · since 9.50.87` ```pascal // bdRecv is a TBinData object. function TransmitHex(const protocolName: string;     const apduHex: string;     bdRecv: TChilkatBase;     maxRecvLen: Integer): Boolean; ``` Sends an APDU to the smart card contained in the currently connected reader. The `protocolName` can be `T0`, `T1`, or `raw`. The APDU (in hexadecimal) to be sent is passed in `apduHex`. The response from the card is contained in `bdRecv`. The `maxRecvLen` is the maximum response size (in bytes) willing to be accepted. Returns True for success, False for failure. ## Events and callbacks Chilkat for Pascal supports three synchronous event callbacks: `OnAbortCheck`, `OnPercentDone`, and `OnProgressInfo`. Each is a property of the class; assign a method of one of your own objects (an *of object* handler) to receive the callbacks, or assign `nil` to unhook. The handler types are declared in the `Chilkat.Base` unit: ```pascal TChilkatAbortCheckEvent = function(Sender: TChilkatBase): Boolean of object; TChilkatPercentDoneEvent = function(Sender: TChilkatBase; PctDone: Integer): Boolean of object; TChilkatProgressInfoEvent = procedure(Sender: TChilkatBase; const Name, Value: string) of object; ``` All Chilkat methods are synchronous, so callbacks are invoked on the thread that called the method -- if the method was called from the main thread, it is safe to access UI elements from the handler. The `HeartbeatMs` property controls the frequency of `OnAbortCheck` callbacks (the default of 0 means no AbortCheck events fire). Returning `True` from an `OnAbortCheck` or `OnPercentDone` handler aborts the running method. ### SCard.AbortCheck (event) `Chilkat 11.7.0 · pascal · SCard · AbortCheck · event` ```pascal // TChilkatAbortCheckEvent = function(Sender: TChilkatBase): Boolean of object; property OnAbortCheck: TChilkatAbortCheckEvent; ``` Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the `HeartbeatMs` property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second. **Event callback implementation:** ```pascal // A handler is a method of one of your own classes, e.g. a form: function TMyObject.SCardAbortCheck(Sender: TChilkatBase): Boolean; begin // Called every HeartbeatMs milliseconds while a method is running. // Return True to abort the method; return False to continue. Result := False; end; ``` **To add an event handler:** ```pascal scard := TSCard.Create; scard.HeartbeatMs := 250; // fire OnAbortCheck 4 times per second scard.OnAbortCheck := MyObject.SCardAbortCheck; ``` ### SCard.PercentDone (event) `Chilkat 11.7.0 · pascal · SCard · PercentDone · event` ```pascal // TChilkatPercentDoneEvent = function(Sender: TChilkatBase; PctDone: Integer): Boolean of object; property OnPercentDone: TChilkatPercentDoneEvent; ``` This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The `pctDone` argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have `pctDone` equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100). The PercentDone callback also acts as an `AbortCheck` event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination. To abort the operation, set the `abort` output argument to `True`. This will cause the method to terminate and return a failure status or corresponding failure value. **Event callback implementation:** ```pascal // A handler is a method of one of your own classes, e.g. a form: function TMyObject.SCardPercentDone(Sender: TChilkatBase; PctDone: Integer): Boolean; begin // PctDone ranges from 1 to 100. WriteLn('Percent done: ', PctDone); // Return True to abort the method; return False to continue. Result := False; end; ``` **To add an event handler:** ```pascal scard := TSCard.Create; scard.OnPercentDone := MyObject.SCardPercentDone; ``` ### SCard.ProgressInfo (event) `Chilkat 11.7.0 · pascal · SCard · ProgressInfo · event` ```pascal // TChilkatProgressInfoEvent = procedure(Sender: TChilkatBase; const Name, Value: string) of object; property OnProgressInfo: TChilkatProgressInfoEvent; ``` This event callback provides `tag name`/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory. Note: Some Chilkat methods don't fire any ProgressInfo events. **Event callback implementation:** ```pascal // A handler is a method of one of your own classes, e.g. a form: procedure TMyObject.SCardProgressInfo(Sender: TChilkatBase; const Name, Value: string); begin WriteLn(Name, ': ', Value); end; ``` **To add an event handler:** ```pascal scard := TSCard.Create; scard.OnProgressInfo := MyObject.SCardProgressInfo; ``` ## Related classes [`BinData`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/pascal/classes/BinData.md), [`JsonObject`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/pascal/classes/JsonObject.md), [`StringTable`](https://www.chilkatsoft.com/ai-docs/v/11.7.0/pascal/classes/StringTable.md)