ZipCrc ActiveX Reference Documentation

ZipCrc

Calculate a Zip CRC checksum for a file or in-memory data.

Object Creation

(Visual Basic 6.0)
Dim obj As New ChilkatZipCrc

(ASP)
set obj = Server.CreateObject("Chilkat_9_5_0.ZipCrc")

(VBScript)
set obj = CreateObject("Chilkat_9_5_0.ZipCrc")

(Delphi)
obj := TChilkatZipCrc.Create(Self);

(FoxPro)
loObject = CreateObject('Chilkat_9_5_0.ZipCrc')

(PowerBuilder)
lole_object = create oleobject
li_rc = lole_object.ConnectToNewObject("Chilkat_9_5_0.ZipCrc")

(SQL Server)
EXEC @hr = sp_OACreate 'Chilkat_9_5_0.ZipCrc', @obj OUT

(Javascript)
var obj = new ActiveXObject("Chilkat_9_5_0.ZipCrc");

Properties

LastMethodSuccess As Long

Introduced in version 9.5.0.52

Indicate whether the last method call succeeded or failed. A value of 1 indicates success, a value of 0 indicates failure. This property is automatically set for method calls. It is not modified by property accesses. The property is automatically set to indicate success for the following types of method calls:

  • Any method that returns a string.
  • Any method returning a Chilkat object, binary bytes, or a date/time.
  • Any method returning a standard boolean status value where success = 1 and failure = 0.
  • Any method returning an integer where failure is defined by a return value less than zero.

Note: Methods that do not fit the above requirements will always set this property equal to 1. For example, a method that returns no value (such as a "void" in C++) will technically always succeed.

Methods

BeginStream()

Provides a way to calculate a CRC by streaming the data a chunk at a time. An application would start by calling BeginStream. Then it would add data by calling MoreData for each additional chunk. After the last chunk has been processed, the EndStream method is called to return the CRC.

CalculateCrc(data As Variant) As Long

Calculates a 32-bit CRC for in-memory byte data. This is the 32-bit CRC that would be found in a Zip file header if a file containing the data was added to a zip archive. Returns the CRC32 of the data.

EndStream() As Long

Finalizes and returns the Zip CRC value calculated by calling BeginStream followed by multiple calls to MoreData.

FileCrc(path As String) As Long

Calculates the CRC32 of a file. The data contained in the file is streamed for the calculation to keep the memory footprint small and constant. Returns the CRC32 of the file.

FileCrcAsync(path As String) As ChilkatTask

Creates an asynchronous task to call the FileCrc method with the arguments provided. (Async methods are available starting in Chilkat v9.5.0.52.)

Note: Async method event callbacks happen in the background thread. Accessing and updating UI elements existing in the main thread may require special considerations.

Returns Nothing on failure

VB6 Programs MUST Call FinalizeThreadPool Just Before Exiting

Asynchronous Methods in VB6 - Be Very Careful with Callbacks

(Classic ASP) How to Run an Asynchronous Task

(Visual FoxPro) How to Run an Asynchronous Task

(PowerBuilder) How to Run an Asynchronous Task

(SQL Server) How to Run an Asynchronous Task

(Visual Basic 6.0) How to Run an Asynchronous Task

(VBScript) How to Run an Asynchronous Task

MoreData(data As Variant)

Adds additional data to the CRC currently being calculated. (See BeginStream for more information.)

ToHex(ByVal crc As Long) As String

Converts a 32-bit integer to a hex string.

Returns Nothing on failure

Events

AbortCheck(abort As Long)

Provides the opportunity for a method call to be aborted. The AbortCheck event is fired periodically based on the value of the HeartbeatMs property. If HeartbeatMs is 0, then no AbortCheck events will fire. As an example, to fire 5 AbortCheck events per second, set the HeartbeatMs property equal to 200.

VB6 Event callback implementation:

Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. See VB6 Async Callbacks

Dim WithEvents myZipcrc As ChilkatZipCrc

Private Sub myZipcrc_AbortCheck(abort As Long)

	'Insert application code here.

End Sub

BinaryData(data As Variant)

Binary data provided by certain methods.

VB6 Event callback implementation:

Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. See VB6 Async Callbacks

Dim WithEvents myZipcrc As ChilkatZipCrc

Private Sub myZipcrc_BinaryData(data As Variant)

	'Insert application code here.

End Sub

PercentDone(ByVal pctDone As Long, abort As Long)

Provides the percentage completed for any method that involves network communications or time-consuming processing (assuming it is a method where a percentage completion can be measured). This event is only fired when it is possible to know a percentage completion, and when it makes sense to express the operation as a percentage completed. The pctDone argument will have a value from 1 to 100. For operations (Chilkat method calls) that complete very quickly, the number of PercentDone callbacks will vary, but the final callback should have a value of 100. For long running operations, no more than one callback per percentage point will occur (for example: 1, 2, 3, ... 98, 99, 100).

The PercentDone callback counts as an AbortCheck event. For method calls that complete quickly such that PercentDone events fire, it may be that AbortCheck events don't fire because the opportunity to abort is already provided in the PercentDone callback. For time consuming operations, where the amount of time between PercentDone callbacks are long, AbortCheck callbacks may be used to allow for the operation to be aborted in a more responsive manner.

The abort output argument provides a means for aborting the operation. Setting it to 1 will cause the method to abort and return a failed status (or whatever return value indicates failure).

VB6 Event callback implementation:

Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. See VB6 Async Callbacks

Dim WithEvents myZipcrc As ChilkatZipCrc

Private Sub myZipcrc_PercentDone(ByVal pctDone As Long, abort As Long)

	'Insert application code here.

End Sub

ProgressInfo(name As String, value As String)

A general name/value event that provides information about what is happening during a method call. To find out what information is available, write code to handle this event and log the name/value pairs. Most are self-explanatory.

VB6 Event callback implementation:

Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. See VB6 Async Callbacks

Dim WithEvents myZipcrc As ChilkatZipCrc

Private Sub myZipcrc_ProgressInfo(name As String, value As String)

	'Insert application code here.

End Sub

TextData(data As String)

Text data provided by certain methods.

VB6 Event callback implementation:

Important: Event callbacks from asynchronous method calls are generally not possible from the ActiveX. See VB6 Async Callbacks

Dim WithEvents myZipcrc As ChilkatZipCrc

Private Sub myZipcrc_TextData(data As String)

	'Insert application code here.

End Sub