DOCUMENT:Q177244 17-MAY-2002 [visualc] TITLE :HOWTO: AsyncDown Demonstrates Asynchronous Data Download PRODUCT :Microsoft C Compiler PROD/VER:winnt:4.2,4.2b,5.0,6.0 OPER/SYS: KEYWORDS:kbfile kbole kbSample kbInternet kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSInet ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - The Microsoft Foundation Classes (MFC), used with: - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2b - Microsoft Visual C++, 32-bit Professional Edition, version 4.2b - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 - Microsoft Windows Internet Services (WinInet) ------------------------------------------------------------------------------- SUMMARY ======= The Asyndown.exe sample demonstrates asynchronous download of data in an MFC ActiveX control. MFC wraps this asynchronous download process in the CAsyncMonikerFile class. MORE INFORMATION ================ The following files are available for download from the Microsoft Download Center: Asyndown.exe For additional information about how to download Microsoft Support files, click the article number below to view the article in the Microsoft Knowledge Base: Q119591 How to Obtain Microsoft Support Files from Online Services Microsoft used the most current virus detection software available on the date of posting to scan this file for viruses. After it is posted, the file is housed on secure servers that prevent any unauthorized changes to the file. An Asynchronous moniker provides a way to download data asynchronously over a network. After a download is first requested, Asynchronous Monikers use a callback interface to indicate that data is available. This data can then be read with an Asynchronous Read operation. A Read operation on an Asynchronous moniker returns immediately even if the operation has not been completed. If there are only 10 bytes available and Read is called with 1K, it does not block but returns with the 10 available bytes at that point in time. It is the caller's responsibility to return later and attempt to read more data when notified through the callback. MFC wraps this asynchronous download process in the CAsyncMonikerFile class. ActiveX controls can use the CDataPathProperty class, derived from CAsyncMonikerFile, to help implement asynchronous control properties. This sample demonstrates how to set up an asynchronous loop using timers to read the data. In the function CDataPathProperty::OnDataAvailable, a timer is set to indicate that data is available. When the timer message is received, the sample reads in blocks of 128 bytes and fills an edit control. If data is not available when the timer message is handled, the timer is turned off. OnDataAvailable turns on the timer if more data arrives later. Please note that the timer duration is intentionally large and data blocks are intentionally small to demonstrate the behavior even with small files. You can test the control either by using the HTML page with the sample or by inserting the control in a control container and setting the DataPath property. The control is not signed so you need to set your security settings appropriately if you want to test the control. Depending on your security setting, you may still be warned that the control is not safe for scripting. (c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Sridhar S. Madhugiri, Microsoft Corporation Additional query words: softlib ====================================================================== Keywords : kbfile kbole kbSample kbInternet kbMFC kbVC420 kbVC500 kbVC600 kbGrpDSInet Technology : kbAudDeveloper kbMFC Version : winnt:4.2,4.2b,5.0,6.0 Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2002.