// Copyright (c) 2006-2009 Nokia Corporation and/or its subsidiary(-ies).

// All rights reserved.

// This component and the accompanying materials are made available

// under the terms of the License "Eclipse Public License v1.0"

// which accompanies this distribution, and is available

// at the URL "http://www.eclipse.org/legal/epl-v10.html".

//

// Initial Contributors:

// Nokia Corporation - initial contribution.

//

// Contributors:

//

// Description:

// Each of these objects may have properties or attributes associated with it. This section

// outlines how applications can retrieve these using the CAF API.

// <hr>

// Different agents may use different terms to describe the same concept. Generic attributes provide a 

// way for applications to query standardised information about a content object. 

// These standardised attributes are given by the enumeration <code>ContentAccess::TAttribute</code>. It is possible 

// for agents to extend this set of attributes, starting from <code>EAgentSpecificAttributeBase</code>. 

// The attribute functions are implemented in <code>ContentAccess::CContent</code>, <code>ContentAccess::CData</code> and 

// <code>ContentAccess::CManager</code>.

// <b> Retrieving a Single Attribute </b>

// The attributes of one content object in a file may not necessarily be the same as the

// attributes of other content objects within the same file. Attributes relate to a single

// content object within a file. 

// It is possible that the attribute may not make sense for a particular content object. In that 

// case the agent will return an error <code>KErrCANotSupported</code>. If an attempt is made to 

// retrieve the attributes of a content object that does not exist the agent will return <code>KErrNotFound</code>.

// The following code fragment illustrates how to retrieve an attribute for a particular

// object within a content file.

// CContent* content = CContent::NewL(uri);

// // check if DRM rights are pending for the object specified by uniqueId

// TInt attributeValue;

// TInt err = content->GetAttribute(ERightsPending, attributeValue, uniqueId);

// if(err == KErrNone)

// // Check the value of the attribute

// if(attributeValue == ETrue)

// // Rights are pending, display waiting for rights countdown

// else if(attributeValue == EFalse)

// // Rights are not pending

// else if(err == KErrCANotSupported)

// // This attribute does not apply to this content object

// else if(err == KErrNotFound)

// // Cannot find the object specified by the given uniqueId

// else if (err != KErrPermissionDenied)

// // Unknown error

// User::Leave(err);

// <b> Retrieving Several Attributes </b>

// For some agent implementations it may be more efficient to retrieve all the attributes for a content

// object in one function call. The <code>ContentAccess::RAttributeSet</code> object is used here to provide a way to

// request and store several attributes.

// Querying two attributes using the CManager API would look like the following:

// // Agent manager

// CManager *manager = CManager::NewLC();

// // Prepare the attributes to query using the CAttributeSet object

// RAttributeSet attributeSet;

// CleanupClosePushL(attributeSet);

// attributeSet.AddL(EProtected);

// attributeSet.AddL(ECanView);

// // Retrieve the attribute values from the agent

// User::LeaveIfError(manager->GetAttributeSet(attributeSet, virtualPath));

// // Check if the content object is protected

// TInt attributeValue;

// TInt err = attributeSet.GetValue(EProtected, attributeValue);

// if(err == KErrNone && attributeValue)

// // content object is DRM protected

// // Check if the content object can be display on screen

// TInt err = attributeSet.GetValue(ECanView, attributeValue);

// if(err == KErrNone && attributeValue)

// // content object has rights that allow it to be displayed on screen

// // Finished	

// CleanupStack::PopAndDestroy(2);		// manager, attributeSet

// <hr>

// String attributes are similar to the attributes described above except the value associated

// with the attribute is a string. A good example of where a string attribute is required is the

// MIME type of a content object within a file. 

// The string attributes are standardised by the <code>ContentAccess::TStringAttribute</code> enumeration. This

// allows applications to request information such as the MIME type in a generic way for all agents.

// Agents can extend this mechanism to provide agent specific attributes starting at 

// <code>EAgentSpecificStringAttributeBase</code>.

// The following example finds the author of a content object.

// CContent* content = CContent::NewL(uri);

// // define a buffer to store the attribute value string

// TBuf <100> buf;

// // retrieve the attribute

// err = content->GetAttribute(EAuthor, authorBuffer, uniqueId);

// // Display the authors name on screen

// if (err == KErrNone)

// DisplayAuthor(buf);

// If the Agent does not support this attribute, it will return <code>KErrCANotSupported</code>.

// <b> Retrieving Several String Attributes </b>

// For some agent implementations it may be more efficient to retrieve several string attributes for a content

// object in one function call. The <code>ContentAccess::RStringAttributeSet</code> object is used here to provide a way to

// request and store several attributes.

// Querying three attributes using the CManager API would look like the following:

// CManager *manager = CManager::NewLC();

// // Prepare the attributes to query using the CAttributeSet object

// RStringAttributeSet stringAttributeSet;

// CleanupClosePushL(stringAttributeSet);

// stringAttributeSet.AddL(ETitle);

// stringAttributeSet.AddL(EAuthor);

// stringAttributeSet.AddL(EDescription);

// // Retrieve the attribute values from the agent

// User::LeaveIfError(manager->GetStringAttributeSet(stringAttributeSet, virtualPath));

// // Display the values

// TBuf <256> value;

// TInt err = stringAttributeSet.GetValue(ETitle, value);

// if(err == KErrNone)

// Printf("Title       : %s", value);

// err = stringAttributeSet.GetValue(EAuthor, value);

// if(err == KErrNone)

// Printf("Author      : %s", value);

// err = stringAttributeSet.GetValue(EDescription, value);

// if(err == KErrNone)

// Printf("Description : %s", value);

// // Finished

// CleanupStack::PopAndDestroy(2);		// manager, stringAttributeSet

// <hr>

// Some agents may expose meta data so they can be read using a \c CData object. The format 

// of these meta-data objects is not specified by the Content Access Framework but could 

// be useful for applications familiar with the agent to read meta data this way.

// \c CData objects for agent specific meta-data can be opened in the same way content objects

// are opened using the <code>ContentAccess::CContent::OpenContentL()</code> function.

// CContent* content = CContent::NewLC(uri);

// // Create an array to store the embedded objects 

// RStreamablePtrArray<CEmbeddedObject> myArray;

// CleanupClosePushL(myArray);

// // Get the embedded "Agent Specific" objects in the current container

// content->GetEmbeddedObjectsL(myArray, EAgentSpecificObject);

// // Get the unique Id of the first meta-data object

// TPtrC aUniqueId = myArray[0]->UniqueId();

// // create a CData object to read the meta data

// CData *myMetaData = content->OpenContentLC(EPeek, aUniqueId);

// // Do something with the data

// // Finished

// CleanupStack::PopAndDestroy(3);		// content, myArray, myMetaData

// <hr>

// 

//

/**

 @page ContentAttributes Content Object Attributes

 As shown in the @ref CContentAPI "Consumer API", a file may consist of many content and container objects.

 - @ref CAFAttributes

 - @ref CAFStringAttributes

 - @ref CAFAgentSpecificMetaData 

 @section CAFAttributes Generic Attributes

 @code

 @endcode

 @code

 @endcode

 @section CAFStringAttributes Generic String attributes

 @code

 @endcode

 @code

 @endcode

 @section CAFAgentSpecificMetaData Agent specific meta-data

 @code

 @endcode

*/