Click to open or copy the ASYNC project files.
This sample creates a control that downloads data asynchronously from a URL. The control implements the IBindStatusCallback interface. Typically, you asynchronously download large binary objects or properties. This allows the control's user interface to remain unblocked during potentially lengthy network operations. The use of asynchronous downloading also gives the user a chance to abort the download. ATL uses WinInet functions internally to implement asynchronous downloading.
ASYNC creates a subclassed edit control with one property called URL. The URL property is a BSTR that represents a URL that points to data. The ASYNC sample uses the ATL CBindStatusCallback class to implement asynchronous downloading. When the control user sets the URL property, ASYNC creates a CBindStatusCallback object. The CBindStatusCallback::StartAsyncDownload method is then called and passed both the URL and a pointer to a callback function. This function, CAtlAsync::OnData, is called by the CBindStatusCallback object and is passed the binary data from the URL as it is received. CAtlAsync::OnData simply sends the received data to the subclassed edit control, where it is displayed.
Running the Sample
Load the AtlAsync.htm file into your web browser. Type a URL into the edit control and press the Go button. This sets the ASYNC control's URL property to the URL you typed and starts the download. As data is downloaded, you will see it displayed in the ASYNC control.
For an example of how to subclass Windows controls using ATL, see the ATL SubEdit sample.
This sample uses the following keywords:
ALT_MSG_MAP; ATLTRACE ; BEGIN_COM_MAP; BEGIN_MSG_MAP; BEGIN_OBJECT_MAP; BEGIN_PROPERTY_MAP; CBindStatusCallback::Download; CComBSTR::Append; CComCoClass; CComControl; CComModule::GetClassObject; CComModule::GetLockCount; CComModule::Init; CComModule::RegisterServer; CComModule::Term; CComModule::UnregisterServer; CComObjectRoot; COM_INTERFACE_ENTRY; COM_INTERFACE_ENTRY_IMPL; DECLARE_REGISTRY_RESOURCEID; DisableThreadLibraryCalls; DLL_PROCESS_ATTACH; DLL_PROCESS_DETACH; DllMain; END_COM_MAP; END_MSG_MAP; END_OBJECT_MAP; END_PROPERTY_MAP; IDataObjectImpl; IDispatchImpl; IObjectSafetyImpl; IOleControlImpl; IOleInPlaceActiveObjectImpl; IOleInPlaceObjectWindowlessImpl; IOleInPlaceObjectWindowlessImpl::SetObjectRects; IOleObjectImpl; IPerPropertyBrowsingImpl; IPersistPropertyBagImpl; IPersistStorageImpl; IPersistStreamInitImpl; IProvideClassInfo2Impl; IQuickActivateImpl; IsWindow; IViewObjectExImpl; MESSAGE_HANDLER; OBJECT_ENTRY; PROP_ENTRY; SendMessage; USES_CONVERSION