How to parse XML files using the CParser class

Comments

16 Sep
2009

Article Review by savaj (20090916)

XML is playing an increasingly important role in the exchange of a wide variety of data on the server. Application may request some data from server in form of XML using predefined protocol, Or send data to server in form of XML using predefined protocol. CParser class, which is used to parse XML, is introduced in Symbian from version 8.1a.

CParser is SAX parser. Interface MContentHandler will gives a callback on start of each tag and at the end of tag, which is useful to parse each tags and attribute of XML file. OnStartElementL() get called for each tag, RTagInfo will gives name of tag and RAttributeArray will each attribute and its value. First parameter of method OnContentL() will contains data of tag.

You can use class CXmlHandler, of this article, to parse XML in your application. Source code with article helps to understand how to use CParser, comments in article will be useful to understand importance of each function.

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GTO India - Hi I tried to parse the cml script using ur code but seeing no parsed result.

Hi I tried to parse the cml script using ur code but seeing no parsed result. Actually I want to parse my script containing many xml nodes , names ,images etc.

I want to parse the images also from the script so I tried ur code first. I succeesfully installed ur code on the device Bur after selcting options when I click "start Parsing" nothing haappens

why is it so I have kept the path as ..\data\example.xml \epoc32\release\winscw\udeb\z\private\A000211F\example.xml

Please help me with ur solution here or mail to svn_k1@yahoo.co.in

GTO_India 12:02, 20 June 2011 (EEST)

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This code example shows how to parse XML file using Symbian OS C++ class, CParser. CParser is basically a SAX (Simple API for XML)-based XML parser.

Article Metadata

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Code Example

Source file: myxmlparser.zip

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Article

Created: antonypr (19 Apr 2007)

Last edited: hamishwillee (18 Sep 2012)

It uses an active object to read the XML file chunk by chunk (see CXmlHandler::StartParsingWithAoL() method. On each chunk, it passes the buffer to the XML parser. When the XML parser finds an element, it calls the respective callback functions, for example CXmlHandler::OnStartElementL() or CXmlHandler::OnEndElementL().

To use CParser class, the XmlFramework.lib has to be included in the .mmp file. For more information about CParser, please visit some links at the end of this page.

XmlHandler.h

#ifndef __XMLHANDLER_H__
#define __XMLHANDLER_H__
 
// INCLUDE FILES
#include <e32base.h>
#include <f32file.h>  //Link against efsrv.lib 
#include <xml\contenthandler.h> // for MContentHandler
#include <xml\parser.h> // for CParser
 
// CLASS DECLARATION
 
using namespace Xml;
 
class CXmlHandler: public CActive, MContentHandler
    {
public: // Constructors and destructor
    static CXmlHandler* NewL();   
    static CXmlHandler* NewLC();   
    virtual ~CXmlHandler();
 
public: // Public methods
    void StartParsingWithAoL( const TDesC& aFileName );
 
private: // Constructors
    CXmlHandler(); 
    void ConstructL();
 
private: // from CActive  
    void DoCancel();  
    void RunL();
 
private: // from MContentHandler
    void OnStartDocumentL( const RDocumentParameters &aDocParam,
        TInt aErrorCode );   
    void OnEndDocumentL( TInt aErrorCode );  
    void OnStartElementL( const RTagInfo &aElement,
        const RAttributeArray &aAttributes, TInt aErrorCode );
 
    void OnEndElementL( const RTagInfo &aElement, TInt aErrorCode );  
    void OnContentL( const TDesC8 &aBytes, TInt aErrorCode );
    void OnStartPrefixMappingL( const RString &aPrefix, const RString &aUri,
        TInt aErrorCode );
 
    void OnEndPrefixMappingL( const RString &aPrefix, TInt aErrorCode );
    void OnIgnorableWhiteSpaceL( const TDesC8 &aBytes, TInt aErrorCode );
    void OnSkippedEntityL( const RString &aName, TInt aErrorCode );  
    void OnProcessingInstructionL( const TDesC8 &aTarget, const TDesC8 &aData,
        TInt aErrorCode);      
    void OnError( TInt aErrorCode ); 
    TAny *GetExtendedInterface( const TInt32 aUid );
 
private: // Private data
    CParser*             iParser;
    HBufC8*              iBuffer;
    RFile                iFile;
 
    };
 
#endif /* __XMLHANDLER_H__ */

XmlHandler.cpp

// INCLUDE FILES
#include <coemain.h>
#include "XmlHandler.h"
 
// CONSTANTS
const TInt KFileBufferSize = 1024; // buffer size for file reading
_LIT8( KXmlMimeType, "text/xml" );
 
// METHODS DEFINITION
 
CXmlHandler* CXmlHandler::NewL()
    {
    CXmlHandler* self = CXmlHandler::NewLC();
    CleanupStack::Pop();
    return self;
    }
 
CXmlHandler* CXmlHandler::NewLC()
    {
    CXmlHandler* self = new ( ELeave ) CXmlHandler();
    CleanupStack::PushL( self );
    self->ConstructL();
    return self;
    }
 
CXmlHandler::~CXmlHandler()
    {
    Cancel();
    delete iParser;
    delete iBuffer;
    }
 
CXmlHandler::CXmlHandler()
    :CActive( EPriorityStandard )
    {
    CActiveScheduler::Add( this );
    }
 
void CXmlHandler::DoCancel()
    {
    iParser->ParseEndL();
    iFile.Close();
    delete iBuffer;
    iBuffer = 0;
    }
 
void CXmlHandler::RunL()
    {
    if ( KErrNone == iStatus.Int() )
        {
        // If the buffer length is zero, it means if we have reached
        // the end of the file.
        if ( iBuffer->Length() == 0)
            {
            iParser->ParseEndL();
            iFile.Close();
            delete iBuffer;
            iBuffer = 0;
            }
 
        // Otherwise, we continue reading the next chunk of the XML file.
        else
            {
            // Parse the next "part" of the XML document.
            iParser->ParseL( *iBuffer );
 
            // Read the next chunk of the file.
            TPtr8 bufferPtr( iBuffer->Des() );
            iFile.Read( bufferPtr, KFileBufferSize, iStatus );
 
            // Don't forget to call this... :)
            SetActive();
            }
        }
    else
        {
        // Do something if error happens.
        }
    }
 
void CXmlHandler::ConstructL()
    {
    iParser = CParser::NewL( KXmlMimeType, *this );
    }
 
void CXmlHandler::StartParsingWithAoL( const TDesC& aFileName )
    {
     // Remember to cancel any outstanding request first.
    if ( IsActive() )
        {
        Cancel();
        }
 
    User::LeaveIfError( iFile.Open( CCoeEnv::Static()->FsSession(), aFileName,
        EFileRead ) );
 
    // Create a buffer to store the file content.
    // Note that this method uses active object to read the file.
    // So we have to call SetActive() at the end. Then we call CParser::ParseL()
    // in RunL() method.
    delete iBuffer;
    iBuffer = 0;
    iBuffer = HBufC8::NewL( KFileBufferSize );
    TPtr8 bufferPtr( iBuffer->Des() );
    iFile.Read( bufferPtr, KFileBufferSize, iStatus );
    SetActive();
 
    // Tell the parser that we are about to parse a XML document.    
    iParser->ParseBeginL();
    }
 
void CXmlHandler::OnStartDocumentL( const RDocumentParameters& /*aDocParam*/,
        TInt aErrorCode )
    {
    if ( KErrNone == aErrorCode )
        {
        // Do something here when the parser at the start of the document.
        }
    else
        {
        // Do something if error happens.
        }
    }
 
void CXmlHandler::OnEndDocumentL( TInt aErrorCode )
    {
    if ( KErrNone == aErrorCode )
        {
        // Do something here when the parser reaches the end of the document.
        }
    }
 
void CXmlHandler::OnStartElementL( const RTagInfo& aElement,
        const RAttributeArray& /*aAttributes*/, TInt aErrorCode )
    {
    if ( KErrNone == aErrorCode )
        {
        // Found start of an element, for example: "<tag>"
        // The name of the element is stored in aElement.LocalName().DesC().
 
        // Do something with the start of an element.
        }
    else
        {
        // Do something if error happens.
        }
    }
 
void CXmlHandler::OnEndElementL( const RTagInfo &aElement, TInt aErrorCode )
    {
    if ( KErrNone == aErrorCode )
        {
        // Found the end of an element, for example: "</tag>"
        // The name of the element is stored in aElement.LocalName().DesC().
 
        // Do something with the end of an element.
        }
    else
        {
        // Do something if error happens.
        }
    }
 
void CXmlHandler::OnContentL( const TDesC8 &aBytes, TInt aErrorCode )
    {
    if ( KErrNone == aErrorCode )
        {
        // aBytes stored the value of the parsed contents.
        }
    else
        {
        // Display error messages here.
        }
    }
 
void CXmlHandler::OnStartPrefixMappingL( const RString& /*aPrefix*/,
        const RString& /*aUri*/, TInt aErrorCode )
    {
    }
 
void CXmlHandler::OnEndPrefixMappingL( const RString& /*aPrefix*/,
        TInt aErrorCode )
    {
    }
 
void CXmlHandler::OnIgnorableWhiteSpaceL( const TDesC8& /*aBytes*/,
        TInt aErrorCode )
    {
    }
 
void CXmlHandler::OnSkippedEntityL( const RString& /*aName*/,
        TInt aErrorCode )
    {
    }
 
void CXmlHandler::OnProcessingInstructionL( const TDesC8& /*aTarget*/,
        const TDesC8& /*aData*/, TInt aErrorCode )
    {
    }
 
void CXmlHandler::OnError( TInt aErrorCode )
    {
    // Do something if error happens.
    }
 
TAny* CXmlHandler::GetExtendedInterface( const TInt32 /*aUid*/ )
    {
    return 0;
    }

download example

• myxmlparser.zip

See Also

• Use the XML Parser in Symbian OS 9
• Example Code of Using XML Parser in Symbian OS