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PERSERVE - IPersistStream Persistent Object Server |
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The PERSERVE sample introduces persistent COM objects. This is the first of four samples covering various techniques for implementing COM object persistence. PERSERVE covers persistence using the implementation of the IPersistStream standard interface. PERTEXT covers persistence using the implementation of the IPersistStreamInit standard interface. PERDRAW covers persistence using the implementation of the IPersistStorage standard interface. PERCLIEN covers how a client exploits the different kind of persistence supported by each of the components in the PERSERVE, PERTEXT, and PERDRAW servers.
The PERSERVE sample introduces the COPageList COM object, which encapsulates a page list. The list contains elements that correspond to pages of text or drawing data. COPageList objects expose a set of interfaces that make the objects connectable, persistent managers of the list data. Client access to this data is available through an IPageList custom interface. COPageList implements the IPageList interface.
A clear architectural distinction is kept between client and server. COPageList provides no graphical user interface (GUI). Instead, the COPageList object relies on the client for all GUI behavior.
The PERCLIEN client provides the GUI display and manages the list of pages the content of which are stored in a compound file that contains both the contents of the list and of each page in that list. The user of PERCLIEN can edit the content of two type of pages: Text pages and drawing pages. Text pages have text data that the user can edit using a simple windowed text editor. Drawing pages have drawing data that the user can edit using free-form, scribble-like functionality based on the earlier STOSERVE and STOCLIEN samples. Both types of editing are done in separate client windows. The details of the client are covered in the PERCLIEN sample. For more information, see PERCLIEN.HTM.
Storage in the compound file is achieved because the components provide persistent COM objects that encapsulate the page list and edited page data. PERSERVE houses a persistent object that encapsulates the single page list kept in each compound file containing such pages. PERTEXT houses a persistent object that encapsulates the edited text data for each text page. PERDRAW houses a persistent object that encapsulates the drawing data for each drawing page.
The COPageList object in the this PERSERVE sample encapsulates the persistent page list data. COPageList implements the IPersistStream standard interface to expose control of the page list storage located in the client-provided stream of a compound file. The COTextPage object in the PERTEXT sample encapsulates the data of an edited text page. COTextPage implements the IPersistStreamInit standard interface to expose control of the text data storage that is located in the client-provided stream of a compound file. In contrast to these stream-based persistent objects, the CODrawPage object in the PERDRAW sample encapsulates the persistent drawing-ink data. CODrawPage implements the IPersistStorage standard interface to expose control of the drawing's ink data storage located in the client-provided substorage of a compound file.
This code sample focuses primarily on COPageList's implementation of the IPersistStream interface to provide stream-based persistence for a COM object. PERSERVE works with the PERCLIEN code sample to illustrate the joint use by client and server of this IPersistStream-based persistence.
COPageList's support for object persistence is the primary means of storing the page list data. COPageList stores its list data in a stream under the root storage of a structured-storage compound file. The compound file has a unique format because of the various streams and storages used. The client identifies these compound files as page files with a .PAG extension. Only one page-list stream is present in each page file. The client controls the use of the containing compound file and provides COPageList with an IStream pointer for its use in loading and saving its list data in the compound file. The IStream pointer is passed to COPageList in method calls to the IPersistStream interface.
COPageList also exposes an IPageList custom interface to manipulate the encapsulated list data. IPageList exposes the Get, Set, Add, Delete, and Clear methods.
Connectable object features are also supported in COPageList. The IConnectionPointContainer interface is exposed, and an appropriate connection point is implemented. In this context, an outgoing custom IPageListSink interface is declared to send notifications to the client.
The two IPageList and IPageListSink custom interfaces are declared in IPAGES.H located in the common INC directory. PAGEGUID.H, which contains the GUIDs for the interfaces and objects, is located in that same directory.
The PERSERVE sample uses the CThreaded facility in APPUTIL to achieve thread safety in the server housing and the class factory. Because PERSERVE.DLL is generally accessed from a Single Threaded Apartment (STA) as an in-process server, COPageList instances are not coded as thread-safe. The CLSID_PageList component is registered as supporting the apartment threading model.
For functional descriptions and a tutorial code tour of PERSERVE, see the Code Tour section in PERSERVE.HTM. For details on setting up the programmatic usage of PERSERVE.DLL, see the Usage section in PERSERVE.HTM. To read PERSERVE.HTM, run TUTORIAL.EXE in the main tutorial directory and click the PERSERVE lesson in the table of lessons. You can also do the same thing by double-clicking the PERSERVE.HTM file after locating the main tutorial directory in Windows Explorer. See also PERCLIEN.HTM in the main tutorial directory for more details on the PERCLIEN client application and how it works with PERSERVE.DLL. You must build PERSERVE.DLL before running the PERCLIEN sample.
The PERSERVE server provides a PageList component that can create instances of the COPageList COM object. COPageList is housed in the PERSERVE.DLL in-process server and is made publicly available as a custom COM component. Like all other servers in this tutorial series, PERSERVE.DLL is a self-registering COM server. It makes the COPageList object type available to clients as the PageList component in the PERSERVE server using a CLSID_PageList registration in the Registry.
PERSERVE's makefile automatically registers its PageList COM component in the registry, which it must do before clients can use PERSERVE.DLL as a server for the PageList component. This self-registration is started in the makefile using the REGISTER.EXE utility built in the REGISTER sample. To build or run PERSERVE.DLL, you must build the REGISTER code sample first.
For details on setting up your system to build and test the code samples in this COM Tutorial series, see TUTORIAL.HTM. The supplied MAKEFILE is Microsoft NMAKE-compatible. To create a debug build, issue the NMAKE command in the Command Prompt window.
To use PERSERVE, a client program does not need to include PERSERVE.H or link to PERSERVE.LIB. A COM client of PERSERVE obtains access solely through COM services and the PageList object's CLSID. For PERSERVE, that CLSID is CLSID_PageList (defined in file PAGEGUID.H in the INC sibling directory). For more information about how the client obtains this access, see the PERCLIEN code sample.
PERSERVE.DLL is intended primarily as a COM server. Although it can be implicitly loaded by linking to its associated .LIB file, it is normally used after an explicit LoadLibrary call, usually from within the CoGetClassObject function. PERSERVE is a self-registering in-process server.
The makefile that builds this sample automatically registers the server in the registry. You can manually initiate its self-registration by issuing the following command at the command prompt in the PERSERVE directory:
nmake register
This assumes that you have a compilation environment set up. If not, you can also directly invoke the REGISTER.EXE command at the command prompt while in the PERSERVE directory.
..\register\register.exe perserve.dll
These registration commands require a prior build of both the REGISTER sample and PERSERVE.DLL.
In this series, the makefiles use the REGISTER.EXE utility from the REGISTER sample. Recent releases of the Microsoft Platform SDK and Visual C++® include a utility, REGSVR32.EXE, which you can use in a similar fashion to register in-process servers and marshaling DLLs.
The client sample and other related samples must be compiled before you can run the client. For more details on building the samples, see Building the Code Samples.
If you have already built the appropriate samples, PERCLIEN.EXE is the client executable to run for this sample.
Files Description
PERSERVE.TXT Short description of sample.
MAKEFILE The generic makefile for building the PERSERVE.DLL
code sample of this lesson.
PERSERVE.H The include file for declaring as imported or defining
as
exported the service functions in PERSERVE.DLL.
PERSERVE.CPP The main implementation file for PERSERVE.DLL. Has
DllMain
and the COM server functions (for example,
DllGetClassObject).
PERSERVE.DEF The module definition file. Exports server housing
functions.
PERSERVE.RC The DLL resource definition file for the executable.
PERSERVE.ICO The icon resource for the executable.
SERVER.H The include file for the server control C++ object.
SERVER.CPP The implementation file for the server control C++
object.
FACTORY.H The include file for the server's class factory COM
objects.
FACTORY.CPP The implementation file for the server's class
factories.
CONNECT.H The include file for the connection point enumerator,
connection point, and connection enumerator classes.
CONNECT.CPP The implementation file for the connection point
enumerator,
connection point, and connection enumerators objects.
PAGELIST.H The include file for the COPageList COM object class.
PAGELIST.CPP The implementation file for the COPageList COM object
class
and the connection points.
PERSERVE uses many of the utility classes and services provided by APPUTIL. For more details on APPUTIL, study the APPUTIL library's source code in the sibling APPUTIL directory and APPUTIL.HTM in the main tutorial directory.
This sample is part of a graduated series of tutorial code samples and assumes that you have had some exposure to the previous samples. It does not revisit earlier topics such as basic interface implementation techniques, COM object construction, in-process server construction, class-factory construction, connectable object construction, and techniques of using structured storage in compound files. For information on these topics, study the earlier tutorial samples.
The major topics covered in this code tour are:
The COPageList COM object is the single object type managed by this PERSERVE in-process server. COPageList is a connectable COM object with an implementation of the IConnectionPointContainer standard interface, an implementation of the IPersistStream standard interface, and an implementation of the IPageList custom interface.
COPageList exposes the IPageList custom interface so clients can perform a small set of operations on the page list that is encapsulated by COPageList. The following is a summary of the IPageList methods from IPAGES.H located in the common INC directory:
Get
Get a page list item for a given page number. This includes
open status, page type, page title, and page data name.
Set
Put a page list item of specified page number with the page's
title and open status.
Add
Add a new page list item of specified type with specified title.
Delete
Delete the page list item that correspondes to the specified
page
number.
Clear
Clear (and delete) all page list items from the page list.
Get, Set, Add, and Delete all act upon individual list entries, while Clear acts upon the entire list. The implementation of IPageList is straightforward and is not covered in detail here. A set of properties for the list is maintained and the list array itself is maintained. For more details, see PAGELIST.H and PAGELIST.CPP.
COPageList manages the array of its list data in RAM. However, because COPageList is also a persistent object, it also manages the persistent image of this list data in a stream of a structured storage compound file. COPageList exposes an implementation of the IPersistStream interface so that clients can control the persistence features of COPageList. The principal focus of this sample is COPageList's implementation of IPersistStream.
The client is responsible for a presentation of the list to the user. PERCLIEN does this with a standard List Box control. The client uses the IPageList interface on COPageList to obtain the data to display in this list box and to update COPageList with any user-requested changes to the list data. The client does not primarily manage the list data. COPageList does this in the PERSERVE server. The client does manage creation or opening of the compound file containing the list data. When the client needs to control the persistence of COPageList it specifies an IStream interface to COPageList. This is typically done during such IPersistStream method-calls as Load and Save. COPageList then uses that stream for all persistent storage of its object-state data.
Two major data constructs are stored for this object-state data: a page list item and the page list properties. The page list data contains an array of the following PAGEITEM structures whose format is declared in PAGELIST.H.
// The PageList item structure.
typedef struct _PAGEITEM
{
SHORT nType; // Page Type.
BOOL bOpen; // Page Open status.
INT iPage; // Page Number.
WCHAR wszDataName[PAGE_NAME_SIZE]; // Page Storage/Stream
Data Name.
WCHAR wszTitle[PAGE_TITLE_SIZE]; // Page Title.
} PAGEITEM;
The nType member contains the page type. Currently the following types are defined in the IPAGES.H file found in the common INC directory.
// Here are the page types. #define PAGETYPE_NONE 0 #define PAGETYPE_DELETED 1 #define PAGETYPE_TEXT 2 #define PAGETYPE_DRAWING 3
The bOpen Boolean member is for future evolution of the application, and is not used by the PERCLIEN client. The intention is to allow a client to restore the opened pages across invocations of the client and doing this requires persistence on the open status of the opened pages.
The iPage member is the page sequence number of the list item. It is used to associate the client's list box item with the associated page data. For example, the client may want to delete the page after the list is loaded from persistent storage. A delete call (through IPageList::Delete) would specify the page number of the page to delete. Because of deletes and other activity on COPageList's dynamic page list, the array index of the items in COPageList's list array may not match the associated page number. Thus, the page associated with the list item that the user sees in the client must be found in COPageList's list array by finding a match on the iPage member. The pages are numbered within the array and are not numbered according to their "slot" in the dynamic list array.
The wszDataName member is the name of the stream in which the page's data is stored. This page data is the text data of text pages and the drawing data of drawing pages. Note that this stream name is a wide character string that supports Unicode. Each page in the compound file has such a named stream for its data. The stream name is an internal, automatically generated name of the forms, Drawing00000 or Text00000. The generation algorithm for this data stream name (see the NextName internal method in PAGELIST.CPP) guarantees that this name will always be unique within the same compound file. PAGE_NAME_SIZE is defined in IPAGES.H as 16. Likewise, PAGE_TITLE_SIZE is defined in IPAGES.H as 64.
The wszTitle member is the user displayable title of the page. This title is displayed for each page in the client list box. This title is a wide character string.
The other important persistent data that is stored in the page list's data stream is a set of properties for the page list. These are properties of the page list and not properties of individual pages and characterize the contents of the entire compound file. The following is the PAGELISTPROPS structure from PAGELIST.H:
// Properties of the PageList.
typedef struct _PAGELISTPROPS
{
LONG lPageListVersion;
LONG lPageListSize;
LONG lPageNameCounter;
WCHAR wszTitle[PAGE_TITLE_SIZE];
WCHAR wszAuthor[PAGE_TITLE_SIZE];
WCHAR wszReserved1[PAGE_TITLE_SIZE];
} PAGELISTPROPS;
The lPageListVersion member holds a version number for the page list. This allows the first member to be checked to determine possible variations in treatment based on the page list version.
The lPageListSize member holds the number of page list items in the page list array.
The lPageNameCounter member holds a counter used in generating unique data names for streams and storages used in the compound file.
The wszTitle, wszAuthor, and wszReserved1 members are for future evolution of the application and are not used by PERSERVE or PERCLIEN.
In the division of labor between client and server, COPageList does not create the compound file that is used to store page list data. The client uses the IPersistStream interface for both the Save and Load of the COPageList's persistent data. The client passes an IStream interface pointer for a stream located in an existing compound file. COPageList then uses the IStream interface to read and write data in the compound file.
Here is the declaration of the COPageList COM object from PAGELIST.H:
class COPageList : public IUnknown
{
public:
// Main Object Constructor & Destructor.
COPageList(IUnknown* pUnkOuter, CServer* pServer);
~COPageList(void);
// A general public method for initializing this newly created
// object. Creates any subordinate arrays, structures, or
objects.
// Not exposed as part of an interface. Used by Class Factory.
HRESULT Init(void);
// Main object IUnknown methods. Non-delegating.
STDMETHODIMP QueryInterface(REFIID, PPVOID);
STDMETHODIMP_(ULONG) AddRef(void);
STDMETHODIMP_(ULONG) Release(void);
private:
// We declare nested class interface implementations here.
class CImpIConnectionPointContainer : public
IConnectionPointContainer
{
public:
// Interface Implementation Constructor & Destructor.
CImpIConnectionPointContainer(COPageList* pCO, IUnknown*
pUnkOuter);
~CImpIConnectionPointContainer(void);
// IUnknown methods.
STDMETHODIMP QueryInterface(REFIID, PPVOID);
STDMETHODIMP_(ULONG) AddRef(void);
STDMETHODIMP_(ULONG) Release(void);
// IConnectionPointContainer methods.
STDMETHODIMP FindConnectionPoint(REFIID,
IConnectionPoint**);
STDMETHODIMP
EnumConnectionPoints(IEnumConnectionPoints**);
private:
// Data private to this interface implementation.
COPageList* m_pCO; // Parent Object back
pointer.
IUnknown* m_pUnkOuter; // Outer unknown for
Delegation.
};
class CImpIPersistStream : public IPersistStream
{
public:
// Interface Implementation Constructor & Destructor.
CImpIPersistStream(COPageList* pCO, IUnknown* pUnkOuter);
~CImpIPersistStream(void);
// IUnknown methods.
STDMETHODIMP QueryInterface(REFIID, PPVOID);
STDMETHODIMP_(ULONG) AddRef(void);
STDMETHODIMP_(ULONG) Release(void);
// IPersistStream methods.
STDMETHODIMP GetClassID(CLSID* pClassID);
STDMETHODIMP IsDirty(void);
STDMETHODIMP Load(IStream* pIStream);
STDMETHODIMP Save(IStream* pIStream, BOOL
bClearDirty);
STDMETHODIMP GetSizeMax(ULARGE_INTEGER* pcbSize);
private:
// Data private to this interface implementation.
COPageList* m_pCO; // Parent Object back
pointer.
IUnknown* m_pUnkOuter; // Outer unknown for
Delegation.
};
class CImpIPageList : public IPageList
{
public:
// Interface Implementation Constructor & Destructor.
CImpIPageList(COPageList* pCO, IUnknown* pUnkOuter);
~CImpIPageList(void);
// IUnknown methods.
STDMETHODIMP QueryInterface(REFIID, PPVOID);
STDMETHODIMP_(ULONG) AddRef(void);
STDMETHODIMP_(ULONG) Release(void);
// IPageList methods.
STDMETHODIMP Get(
INT iPage,
BOOL* pbOpen,
SHORT* pnType,
WCHAR* pwszTitle,
WCHAR* pwszDataName);
STDMETHODIMP Set(
INT iPage,
SHORT nOpenStatus,
WCHAR* pwszNewTitle);
STDMETHODIMP Add(
INT iPage,
SHORT nType,
WCHAR* pwszTitle,
INT* piNewPage);
STDMETHODIMP Delete(INT iPage);
STDMETHODIMP Clear(void);
private:
// Private utility methods of this interface
implementation.
HRESULT FindSlot(INT iPage, LONG* plSlot);
HRESULT NextSlot(INT iPage, LONG* plSlot);
HRESULT NextName(SHORT nType, WCHAR* pwszDataName);
// Data private to this interface implementation of
IPageList.
COPageList* m_pCO; // Parent Object back
pointer.
IUnknown* m_pUnkOuter; // Outer unknown for
Delegation.
};
// Make the otherwise private and nested interface
implementations
// friends to COM object instantiations of this COM object
class.
friend CImpIConnectionPointContainer;
friend CImpIPersistStream;
friend CImpIPageList;
// Private method of main connectable COPageList COM object to
// broadcast event notifications to all connected listening
sinks.
HRESULT NotifySinks(PAGELIST_EVENT PageListEvent, INT iPage);
// Private method to Clear entire page list array.
HRESULT Clear(void);
// Private data of COPageList COM objects.
// Nested IConnectionPointContainer implementation
instantiation.
CImpIConnectionPointContainer m_ImpIConnectionPointContainer;
// Nested IPersistStream implementation instantiation.
CImpIPersistStream m_ImpIPersistStream;
// Nested IPageList implementation instantiation. This
IPageList
// interface is instantiated as a native interface of
COPageList.
CImpIPageList m_ImpIPageList;
// Main Object reference count.
ULONG m_cRefs;
// Outer unknown (aggregation & delegation).
IUnknown* m_pUnkOuter;
// Pointer to this component server's control object.
CServer* m_pServer;
// The array of connection points for this connectable COM
object.
IConnectionPoint* m_aConnectionPoints[MAX_CONNECTION_POINTS];
// The following private data and methods constitute the
working
// heart of COPageList as an actual application object.
PAGELISTPROPS m_PageListProps;// For file storage.
PAGEITEM* m_paPageList; // Dynamic page list array
pointer.
LONG m_lPageListEnd; // Current end of the page
list.
LONG m_lPageListMax; // Current end of the page
list array.
BOOL m_bDirty; // RAM doesn't match
file--save needed.
CLSID m_ClassID; // CLSID of this COM Object.
};
COPageList has nested implementations of the IUnknown, IConnectionPointContainer, IPersistStream, and IPageList interfaces. The techniques of these interface implementations follow the pattern used in many previous samples. Implementation of IUnknown was introduced in the COMOBJ sample. IConnectionPointContainer was introduced in the CONSERVE sample. IPageList is a custom interface that is introduced in this sample, but its implementation is very similar to custom interface implementations in previous samples.
The m_PageListProps member is a structure holds various properties of the page list. See above for a summary. The m_bDirty member is used internally to determine when the RAM-resident page list array has changed relative to the last time it was loaded from or saved to persistent storage. The m_ClassID stores the CLSID of the COPageList component for later use within the methods of COPageList. The m_lPageListEnd and m_lPageListMax members are used to maintain the currently active content of the page list array. The index of the current end of the array is kept in m_lPageListEnd. This end index can vary up to the maximum index kept in m_lPageListMax. The array can grow dynamically at run-time.
COPageList manages this page list array in RAM. The main pointer to this array is kept in the m_paPageList variable. The array is initially allocated during IPersistStream::Load after COPageList is created. The Load method is covered in more detail below.
The implementation of the IPersistStream standard interface deserves a more detailed examination. By studying each of the IPersistStream methods, you can see how the implementation of the IPersistStream interface gives persistence to the property and page list data in COPageList. If you have not used streams (IStream) or storages (IStorage) in structured storage compound files, see the STOSERVE and STOCLIEN samples for coverage of this topic. The IPersistStream methods declared above are as follows:
STDMETHODIMP GetClassID(CLSID* pClassID);
STDMETHODIMP IsDirty(void);
STDMETHODIMP Load(IStream* pIStream);
STDMETHODIMP Save(IStream* pIStream, BOOL bClearDirty);
STDMETHODIMP GetSizeMax(ULARGE_INTEGER* pcbSize);
Clients call the GetClassID method to obtain from COPageList its component CLSID. This method is really inherited from the IPersist interface from which IPersistStream is derived. The following is the implementation of GetClassID from PAGELIST.CPP:
STDMETHODIMP COPageList::CImpIPersistStream::GetClassID(
CLSID* pClassID)
{
HRESULT hr = E_POINTER;
if (NULL != pClassID)
{
// Use overloaded '=' operator to copy the Class ID.
*pClassID = m_pCO->m_ClassID;
hr = NOERROR;
}
return hr;
}
This simple method uses the overloaded '=' operator to copy COPageList's main copy of the CLSID to the client's address space using the specified pClassID pointer. The convenient overloading of the '=' operator is provided in the COM and OLE header files included at the front of PAGELIST.CPP. The m_ClassID value was initially assigned the value CLSID_PageList in COPageList's constructor. CLSID_PageList is defined in PAGEGUID.H located in the common INC directory. This file also contains other GUIDs--such as interface IIDs--that are used in the PERSERVE, PERTEXT, PERDRAW, and PERCLIEN samples.
Clients call the IsDirty method to determine if changes have been made to this COPageList's persistent data since it was last loaded, initialized, or saved. The following is the implementation of IsDirty from PAGELIST.CPP:
STDMETHODIMP COPageList::CImpIPersistStream::IsDirty(
void)
{
HRESULT hr = E_FAIL;
hr = m_pCO->m_bDirty ? S_OK : S_FALSE;
return hr;
}
This method simply returns the current "dirty" status of the RAM-resident data in terms of the standard HRESULT return codes of S_OK or S_FALSE. S_OK means the data needs saving; S_FALSE means the data matches its counterpart in persistent storage.
Clients call the Load method is called to command COPageList to load its persistent data from a specified stream in a compound file starting at the current seek pointer offset. Thus, the client supplies the stream to COPageList; the stream is not created by COPageList. The Load method assumes that the stream's seek pointer is the same as it was before Save was last called. The method must leave the seek pointer with the same value it had when Save was last completed regardless of success or failure of the load. The rationale for these seek pointer rules is that IPersistStream can support a consecutive series of stored COPageList object states. The client controls the stream and, if the seek pointer rules are followed within Load and Save, then the client can issue a series of Save calls. Between these calls the client may issue other interface calls to COPageList that could change the data state of COPageList. The consecutive series that are saved would then reflect different data states of the same COPageList object.
The Load method implementation should not store a copy of the passed pIStream pointer within COPageList. The passed stream interface pointer should be used only within this method call. Here is the implementation of Load from PAGELIST.CPP.
STDMETHODIMP COPageList::CImpIPersistStream::Load(
IStream* pIStream)
{
HRESULT hr = E_POINTER;
PAGEITEM* paPageList;
ULONG ulToRead, ulReadIn;
LONG lNewArraySize;
PAGELISTPROPS NewProps;
if (NULL != pIStream)
{
// We have the PageList data stream. First read the
// PageList Properties.
ulToRead = sizeof(PAGELISTPROPS);
hr = pIStream->Read(
&NewProps,
ulToRead,
&ulReadIn);
if (SUCCEEDED(hr) && ulToRead != ulReadIn)
hr = E_FAIL;
if (SUCCEEDED(hr))
{
// Deal with the different PageList versions.
switch (NewProps.lPageListVersion)
{
case PAGELIST_VERSION10:
// Allocate a page list array big enough--add some extra
// for later expansion by user.
lNewArraySize = NewProps.lPageListSize + PAGELIST_ALLOC;
paPageList = new PAGEITEM[(LONG) lNewArraySize];
if (NULL != paPageList)
{
// Delete the entire old Page List array.
if (NULL != m_pCO->m_paPageList)
delete [] m_pCO->m_paPageList;
// Assign the new array.
m_pCO->m_paPageList = paPageList;
m_pCO->m_lPageListMax = lNewArraySize;
// Now read the complete array of Page List items.
ulToRead = NewProps.lPageListSize * sizeof(PAGEITEM);
hr = pIStream->Read(m_pCO->m_paPageList,
ulToRead, &ulReadIn);
if (SUCCEEDED(hr) && ulToRead != ulReadIn)
hr = E_FAIL;
if (SUCCEEDED(hr))
{
// Rig COPageList to use the PAGELISTPROPS info.
m_pCO->m_lPageListEnd = NewProps.lPageListSize -
1;
// Copy the new properties into current properties.
memcpy(
&m_pCO->m_PageListProps,
&NewProps,
sizeof(PAGELISTPROPS));
}
}
else
hr = E_OUTOFMEMORY;
break;
default:
hr = E_FAIL; // Bad version.
break;
}
}
}
// Notify all other connected clients that PageList is now
loaded.
// If we didn't load then clear to a safe, empty Page List
array.
if (SUCCEEDED(hr))
m_pCO->NotifySinks(PAGELIST_EVENT_LOADED,0);
else
m_pCO->Clear();
return hr;
}
Load is called by a client when this COPageList object already has a persistent state stored in a stream. A complete copy of that state data is read from the stream into newly allocated, RAM-resident space for the data. Two kinds of state data are concatenated in the stream: a group of object properties followed by the page list array. The Load method first reads the PAGELISTPROPS properties structure into a temporary NewProps. If the load is successful, these properties are copied to COPageList::m_PageListProps. This is done to allow reverting to the current COPageList data if the entire load of new data is not safely completed.
After the m_PageListProps are read, the lPageListVersion property is used in a switch statement. This allows for different load behavior or data formats based on the version of the data that was stored. Because the version number is the first thing in the stream's object data, it can be read independently to determine how to deal with the data that follows. The lPageListSize property is used to allocate a new array in RAM that is big enough for the array data stored in the stream. After the array is allocated, the page list data is read into that array from the stream. At this point COPageList has been loaded from persistent storage.
If the load is successful, a call to the internal NotifySinks method notifies all connected clients that the load was completed. This notification to the client usually triggers an appropriate display of the newly loaded data. This notification makes use of COPageList's connectable object features. If the load was unsuccessful, a call to the internal Clear method clears the page list to a safe, empty list.
Clients call the Save method to command COPageList to save its persistent data from RAM to a specified stream in a compound file starting at the current seek pointer offset. As with the Load method, the client supplies the stream interface to Save. On exit from this method the seek pointer is assumed to be at the end of the data saved. Again, as with the Load method, the rules governing the seek pointer in the Load and Save methods allow a series of contiguous persistent objects to be saved into the same stream.
The Save method implementation should not store a copy of the passed pIStream pointer within COPageList. The passed stream interface pointer should be used only within this method call. The following is the implementation of Save from PAGELIST.CPP:
STDMETHODIMP COPageList::CImpIPersistStream::Save(
IStream* pIStream,
BOOL bClearDirty)
{
HRESULT hr = E_POINTER;
ULONG ulToWrite, ulWritten;
if (NULL != pIStream)
{
// Got a stream. Now write data into it.
// First write PAGELISTPROPS structure.
m_pCO->m_PageListProps.lPageListSize =
m_pCO->m_lPageListEnd + 1;
ulToWrite = sizeof(PAGELISTPROPS);
hr = pIStream->Write(&m_pCO->m_PageListProps,
ulToWrite, &ulWritten);
if (SUCCEEDED(hr) && ulToWrite != ulWritten)
hr = STG_E_CANTSAVE;
if (SUCCEEDED(hr))
{
// Now write the complete array of Page List Data.
ulToWrite = m_pCO->m_PageListProps.lPageListSize *
sizeof(PAGEITEM);
hr = pIStream->Write(m_pCO->m_paPageList, ulToWrite,
&ulWritten);
if (SUCCEEDED(hr) && ulToWrite != ulWritten)
hr = STG_E_CANTSAVE;
if (SUCCEEDED(hr))
{
// Clear this COM object's dirty flag if instructed.
Otherwise,
// preserve its content.
if (bClearDirty)
m_pCO->m_bDirty = FALSE;
}
}
}
// Notify all other connected clients that PageList is now
saved.
if (SUCCEEDED(hr))
m_pCO->NotifySinks(PAGELIST_EVENT_SAVED,-1);
return hr;
}
The Save method is essentially the reverse of the Load method. The content of COPageList's m_PageListProps structure is written into the specified stream at the stream's current seek pointer offset. This structure is essentially a properties header at the front of the state data. If the PAGELISTPROPS data is successfully saved, the current array of page list data (located in RAM at m_paPageList) is written to the stream. The seek pointer is left pointing just past the end of the saved array. In either of these data writes to the stream, if the amount of data actually written does not equal the amount attempted, the Save method is aborted and returns STG_E_CANTSAVE.
A bClearDirty parameter determines if this method should clear COPageList's m_bDirty flag. If bClearDirty is TRUE then COPageList::m_bDirty is set to FALSE (that is, cleared). Usually, a Save will achieve a match between the RAM-resident data and its corresponding image stored in the stream. However, there may be cases when you want to issue a save to a stream while not clearing COPageList's dirty flag. This might occur if the client is saving a copy of the data state to a stream that is different than the current unsaved stream. If COPageList is not saved to the original unsaved stream, the state of m_bDirty would need to be preserved across the operation. A value of FALSE for the bClearDirty parameter accomplishes this preservation.
If the save is successful, a call to the internal NotifySinks method notifies all connected clients that the save was completed.
Clients call the GetSizeMax method to obtain the maximum size of the state data that can be saved when the Save method is next called. The following is the implementation of GetSizeMax from PAGELIST.CPP:
STDMETHODIMP COPageList::CImpIPersistStream::GetSizeMax(
ULARGE_INTEGER* pcbSize)
{
HRESULT hr = E_POINTER;
DWORD dwProps, dwData;
if (NULL != pcbSize)
{
dwProps = sizeof(PAGELISTPROPS);
dwData = (m_pCO->m_lPageListEnd+1) * sizeof(PAGEITEM);
ULISet32(*pcbSize, dwProps+dwData);
hr = NOERROR;
}
return hr;
}
The caller passes the address of a ULARGE_INTEGER variable that the GetSizeMax method assigns. The client can use this to set the size of a stream using IStream::SetSize, which may be necessary if the client is saving multiple objects in the same stream. If known in advance within COPageList, GetSizeMax should return the maximum potential size that a future Save would consume in the stream.
COPageList exposes the IConnectionPointContainer interface so clients can connect to COPageList in order to receive notifications of specified events that occur in COPageList. Exposing this interface makes COPageList a connectable object. A client can call QueryInterface for this interface and use it to obtain the object's connection points.
Basically, the client implements what is called a sink which is sink object with a sink interface. The sink interface receives outgoing event notification calls from COPageList after the sink is properly connected by the client to a COPageList instance. The client makes the connection by using a connection point object that is managed by COPageList. There can be numerous connection points on a single connectable COM object. In the PERSERVE sample, COPageList has only one connection point, which handles page list events. For more details about how clients participate, see the PERCLIEN sample.
Any number of clients can connect to a single connection point. The CONNPOINT_PAGELISTSINK connection point in COPageList maintains a group of connections that can grow dynamically at run time. The full implementation of COPageList's connectable object support is coded in files CONNECT.H and CONNECT.CPP and will not be covered here. The construction is very similar to that in the CONSERVE code sample.
The PERCLIEN client implements appropriate sink objects for the connection points it expects to find in COPageList. From the context of COPageList, the sink object that PERCLIEN implements exposes the IPageListSink interface. This is the outgoing interface used by COPageList to notify PERCLIEN of various events in COPageList. Here is a summary of the methods in IPageListSink from IPAGES.H in the common INC directory.
Loaded
The PageList was loaded from persistent storage.
Saved
The PageList was saved to persistent storage.
Cleared
The entire PageList was cleared.
PageAdded(INT iPage);
A new PageItem was added to the PageList.
PageDeleted(INT iPage);
A PageItem was deleted from the PageList.
PageSet(INT iPage);
A PageItem entry was set with new data.
These methods are largely self-explanatory. Although the sink must implement all these methods in some fashion, many are implemented as stubs and are not used in the PERSERVE or PERCLIEN samples.
An important method used in these samples is the Loaded method. When the client tells COPageList to load a new page list from file, COPageList needs a way to notify the client when the new data is loaded. To do this, COPageList calls IPageListSink::Loaded on the client sink. The client is thereby signaled that it can display the newly loaded data.
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