CAsyncMonikerFile Class

The latest version of this topic can be found at CAsyncMonikerFile Class.

Provides functionality for the use of asynchronous monikers in ActiveX controls (formerly OLE controls).

Syntax

class CAsyncMonikerFile : public CMonikerFile  

Members

Public Constructors

Public Methods

Protected Methods

Remarks

Derived from CMonikerFile, which in turn is derived from COleStreamFile, CAsyncMonikerFile uses the IMoniker interface to access any data stream asynchronously, including loading files asynchronously from a URL. The files can be datapath properties of ActiveX controls.

Asynchronous monikers are used primarily in Internet-enabled applications and ActiveX controls to provide a responsive user-interface during file transfers. A prime example of this is the use of CDataPathProperty to provide asynchronous properties for ActiveX controls. The CDataPathProperty object will repeatedly get a callback to indicate availability of new data during a lengthy property exchange process.

For more information about how to use asynchronous monikers and ActiveX controls in Internet applications, see the following articles:

• Internet First Steps: Asynchronous Monikers

• Internet First Steps: ActiveX Controls

Inheritance Hierarchy

CObject

CFile

COleStreamFile

CMonikerFile

CAsyncMonikerFile

Requirements

Header: afxole.h

CAsyncMonikerFile::CAsyncMonikerFile

Constructs a CAsyncMonikerFile object.

CAsyncMonikerFile();

Remarks

It does not create the IBindHost interface. IBindHost is used only if you provide it in the Open member function.

For a description of the IBindHost interface, see the Windows SDK.

CAsyncMonikerFile::Close

Call this function to close and release all resources.

virtual void Close();

Remarks

Can be called on unopened or already closed files.

CAsyncMonikerFile::CreateBindStatusCallback

Creates a COM object that implements IBindStatusCallback.

virtual IUnknown* CreateBindStatusCallback(IUnknown* pUnkControlling);

Parameters

pUnkControlling
A pointer to the controlling unknown (the outer IUnknown) or NULL if aggregation is not being used.

Return Value

If pUnkControlling is not NULL, the function returns a pointer to the inner IUnknown on a new COM object supporting IBindStatusCallback. If pUnkControlling is NULL, the function returns a pointer to an IUnknown on a new COM object supporting IBindStatusCallback.

Remarks

CAsyncMonikerFile requires a COM object that implements IBindStatusCallback. MFC implements such an object, and it is aggregatable. You can override CreateBindStatusCallback to return your own COM object. Your COM object can aggregate MFC's implementation by calling CreateBindStatusCallback with the controlling unknown of your COM object. COM objects implemented using the CCmdTarget COM support can retrieve the controlling unknown using CCmdTarget::GetControllingUnknown.

Alternately, your COM object can delegate to MFC's implementation by calling CreateBindStatusCallback( NULL ).

CAsyncMonikerFile::Open calls CreateBindStatusCallback.

For more information about asynchronous monikers and asynchronous binding, see the IBindStatusCallback interface and How Asynchronous Binding and Storage Work. For a discussion of aggregation, see Aggregation. All three topics are in the Windows SDK.

CAsyncMonikerFile::GetBindInfo

Called from the client of an asynchronous moniker to tell the asynchronous moniker how it wants to bind.

virtual DWORD GetBindInfo() const;  

Return Value

Retrieves the settings for IBindStatusCallBack. For a description of the IBindStatusCallback interface, see the Windows SDK.

Remarks

The default implementation sets the binding to be asynchronous, to use a storage medium (a stream), and to use the data-push model. Override this function if you want to change the behavior of the binding.

One reason for doing this would be to bind using the data-pull model instead of the data-push model. In a data-pull model, the client drives the bind operation, and the moniker only provides data to the client when it is read. In a data-push model, the moniker drives the asynchronous bind operation and continuously notifies the client whenever new data is available.

CAsyncMonikerFile::GetBinding

Call this function to retrieve a pointer to the asynchronous transfer binding.

IBinding* GetBinding() const;  

Return Value

A pointer to the IBinding interface provided when asynchronous transfer begins. Returns NULL if for any reason the transfer cannot be made asynchronously.

Remarks

This allows you to control the data transfer process through the IBinding interface, for example, with IBinding::Abort, IBinding::Pause, and IBinding::Resume.

For a description of the IBinding interface, see the Windows SDK.

CAsyncMonikerFile::GetFormatEtc

Call this function to retrieve the format of the data in the stream.

FORMATETC* GetFormatEtc() const;  

Return Value

A pointer to the Windows structure FORMATETC for the currently opened stream. Returns NULL if the moniker has not been bound, if it is not asynchronous, or if the asynchronous operation has not begun.

CAsyncMonikerFile::GetPriority

Called from the client of an asynchronous moniker as the binding process starts to receive the priority given to the thread for the binding operation.

virtual LONG GetPriority() const;  

Return Value

The priority at which the asynchronous transfer will take place. One of the standard thread priority flags: THREAD_PRIORITY_ABOVE_NORMAL, THREAD_PRIORITY_BELOW_NORMAL, THREAD_PRIORITY_HIGHEST, THREAD_PRIORITY_IDLE, THREAD_PRIORITY_LOWEST, THREAD_PRIORITY_NORMAL, and THREAD_PRIORITY_TIME_CRITICAL. See the Windows function SetThreadPriority for a description of these values.

Remarks

GetPriority should not be called directly. THREAD_PRIORITY_NORMAL is returned by the default implementation.

CAsyncMonikerFile::OnDataAvailable

An asynchronous moniker calls OnDataAvailable to provide data to the client as it becomes available, during asynchronous bind operations.

virtual void OnDataAvailable(DWORD dwSize, DWORD bscfFlag);

Parameters

dwSize
The cumulative amount (in bytes) of data available since the beginning of the binding. Can be zero, indicating that the amount of data is not relevant to the operation, or that no specific amount became available.

bscfFlag
A BSCF enumeration value. Can be one or more of the following values:

• BSCF_FIRSTDATANOTIFICATION Identifies the first call to OnDataAvailable for a given bind operation.

• BSCF_INTERMEDIATEDATANOTIFICATION Identifies an intermediary call to OnDataAvailable for a bind operation.

• BSCF_LASTDATANOTIFICATION Identifies the last call to OnDataAvailable for a bind operation.

Remarks

The default implementation of this function does nothing. See the following example for a sample implementation.

Example

void CMyMoniker::OnDataAvailable(DWORD dwSize, DWORD bscfFlag)
{
   if ((bscfFlag & BSCF_FIRSTDATANOTIFICATION) != 0)
   {
      m_dwReadBefore = 0;
      m_strText.Empty();
   }

   DWORD dwArriving = dwSize - m_dwReadBefore;

   if (dwArriving > 0)
   {
      int nLen = m_strText.GetLength();
      ASSERT((DWORD)nLen == m_dwReadBefore);
      LPTSTR psz = m_strText.GetBuffer(nLen + dwArriving);
      Read(psz + nLen, dwArriving);
      m_strText.ReleaseBuffer(nLen + dwArriving);
      m_dwReadBefore = dwSize;
   }
}

CAsyncMonikerFile::OnLowResource

Called by the moniker when resources are low.

virtual void OnLowResource();

Remarks

The default implementation calls GetBinding( )-> Abort( ).

CAsyncMonikerFile::OnProgress

Called by the moniker repeatedly to indicate the current progress of this bind operation, typically at reasonable intervals during a lengthy operation.

virtual void OnProgress(
    ULONG ulProgress,  
    ULONG ulProgressMax,  
    ULONG ulStatusCode,  
    LPCTSTR szStatusText);

Parameters

ulProgress
Indicates the current progress of the bind operation relative to the expected maximum indicated in ulProgressMax.

ulProgressMax
Indicates the expected maximum value of ulProgress for the duration of calls to OnProgress for this operation.

ulStatusCode
Provides additional information regarding the progress of the bind operation. Valid values are taken from the BINDSTATUS enumeration. See Remarks for possible values.

szStatusText
Information about the current progress, depending on the value of ulStatusCode. See Remarks for possible values.

Remarks

Possible values for ulStatusCode (and the szStatusText for each value) are:

BINDSTATUS_FINDINGRESOURCE
The bind operation is finding the resource that holds the object or storage being bound to. The szStatusText provides the display name of the resource being searched for (for example, "www.microsoft.com").

BINDSTATUS_CONNECTING
The bind operation is connecting to the resource that holds the object or storage being bound to. The szStatusText provides the display name of the resource being connected to (for example, an IP address).

BINDSTATUS_SENDINGREQUEST
The bind operation is requesting the object or storage being bound to. The szStatusText provides the display name of the object (for example, a file name).

BINDSTATUS_REDIRECTING
The bind operation has been redirected to a different data location. The szStatusText provides the display name of the new data location.

BINDSTATUS_USINGCACHEDCOPY
The bind operation is retrieving the requested object or storage from a cached copy. The szStatusText is NULL.

BINDSTATUS_BEGINDOWNLOADDATA
The bind operation has begun receiving the object or storage being bound to. The szStatusText provides the display name of the data location.

BINDSTATUS_DOWNLOADINGDATA
The bind operation continues to receive the object or storage being bound to. The szStatusText provides the display name of the data location.

BINDSTATUS_ENDDOWNLOADDATA
The bind operation has finished receiving the object or storage being bound to. The szStatusText provides the display name of the data location.

BINDSTATUS_CLASSIDAVAILABLE
An instance of the object being bound to is just about to be created. The szStatusText provides the CLSID of the new object in string format, allowing the client an opportunity to cancel the bind operation, if desired.

CAsyncMonikerFile::OnStartBinding

Override this function in your derived classes to perform actions when binding is starting up.

virtual void OnStartBinding();

Remarks

This function is called back by the moniker. The default implementation does nothing.

CAsyncMonikerFile::OnStopBinding

Called by the moniker at the end of the bind operation.

virtual void OnStopBinding(HRESULT hresult, LPCTSTR szError);

Parameters

hresult
An HRESULT that is the error or warning value.

szErrort
A character string describing the error.

Remarks

Override this function to perform actions when the transfer is stopped. By default, the function releases IBinding.

For a description of the IBinding interface, see the Windows SDK.

CAsyncMonikerFile::Open

Call this member function to open a file asynchronously.

virtual BOOL Open(
    LPCTSTR lpszURL,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    IMoniker* pMoniker,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    LPCTSTR lpszURL,
    IBindHost* pBindHost,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    IMoniker* pMoniker,
    IBindHost* pBindHost,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    LPCTSTR lpszURL,
    IServiceProvider* pServiceProvider,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    IMoniker* pMoniker,
    IServiceProvider* pServiceProvider,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    LPCTSTR lpszURL,
    IUnknown* pUnknown,
    CFileException* pError = NULL);
 
virtual BOOL Open(
    IMoniker* pMoniker,
    IUnknown* pUnknown,
    CFileException* pError = NULL);

Parameters

lpszURL
A pointer to file to be opened asynchronously. The file can be any valid URL or filename.

pError
A pointer to the file exceptions. In the event of an error, it will be set to the cause.

pMoniker
A pointer to the asynchronous moniker interface IMoniker, a precise moniker that is the combination of the document's own moniker, which you can retrieve with IOleClientSite::GetMoniker( OLEWHICHMK_CONTAINER ), and a moniker created from the path name. The control can use this moniker to bind, but this is not the moniker the control should save.

pBindHost
A pointer to the IBindHost interface that will be used to create the moniker from a potentially relative pathname. If the bind host is invalid or does not provide a moniker, the call defaults to Open( lpszFileName,pError). For a description of the IBindHost interface, see the Windows SDK.

pServiceProvider
A pointer to the IServiceProvider interface. If the service provider is invalid or fails to provide the service for IBindHost, the call defaults to Open( lpszFileName,pError).

pUnknown
A pointer to the IUnknown interface. If IServiceProvider is found, the function queries for IBindHost. If the service provider is invalid or fails to provide the service for IBindHost, the call defaults to Open( lpszFileName,pError).

Return Value

Nonzero if the file is opened successfully; otherwise 0.

Remarks

This call initiates the binding process.

You can use a URL or a filename for the lpszURL parameter. For example:

               CMyMoniker* pMyMoniker = new CMyMoniker();
               pMyMoniker->Open(_T("https://www.microsoft.com"));

– or –

               CMyMoniker* pMyMoniker = new CMyMoniker();
               pMyMoniker->Open(_T("file:c:\\mydata.dat"));

See Also

CMonikerFile Class
Hierarchy Chart
CMonikerFile Class
CDataPathProperty Class