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<concept id="GUID-B5CC77D2-5871-51D8-B359-77EFC081B423" xml:lang="en"><title>Files

Containing Multiple Content Objects</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Content Access Framework provides a generic mechanism for exploring files

that contain multiple content objects. These files are often referred to as

archive files. This can be <filepath>.ZIP</filepath> compression archive or

a DRM protected archive, such as an OMA <filepath>.DCF</filepath> file. An

application can explore the content objects inside a file using the <xref href="GUID-0F5CE9B5-E674-3962-8376-CFB1ECB2F601.dita#GUID-0F5CE9B5-E674-3962-8376-CFB1ECB2F601/GUID-FC40011B-32D3-328B-BB59-35BEF46A215A"><apiname>ContentAccess::CContent</apiname></xref> class. </p>

<section><title>Structure of a file containing multiple content objects</title> <p>An

archive file can have content objects and meta-data or information associated

with the content. This meta-data can include information, such as the MIME

type of the content, the encryption algorithm, the compressed size of the

content. This information can be retrieved from the attributes related to

a content object, see <xref href="GUID-B6912FE7-4C2A-5FC7-BDA8-702CA2C0214A.dita">Content

Object Attributes</xref>. </p> <p>The content and meta-data may also be arranged

in a hierachy with container objects grouping content objects together. A

typical archive can have a complex structure as the example shown below: </p> <fig id="GUID-13E44820-5D67-580F-BC0D-26A935EB1F72">

<image href="GUID-4B7410B2-849B-5E89-97BF-E06613F600CB_d0e607160_href.png" placement="inline"/>

</fig> <p>In this scenario, the file itself can be considered as the top level

container. All other content, containers and meta-data are nested inside.

In an archive file, applications can quickly search for the content objects

they are interested in by using <xref href="GUID-FC40011B-32D3-328B-BB59-35BEF46A215A.dita#GUID-FC40011B-32D3-328B-BB59-35BEF46A215A/GUID-FA4BB868-3297-39F0-BAB8-C4BF4F5A2B60"><apiname>ContentAccess::CContent::Search()</apiname></xref>,

see <xref href="GUID-09A760FD-4C2A-5F79-91F2-DCC25A63699C.dita">Consumer API Tutorial</xref>. </p> </section>

<section id="GUID-34F8F3F7-B497-5BBE-B282-33DF7DB0D560"><title>Identifying

a content object within a file</title> <p>Archive files containing several

content objects cannot be referred to using just the URI of the file. The

Content Access Framework uses a concept of virtual paths to identify content

objects within a file. The virtual path is a combination of the file URI and

a unique identifier supplied by the agent: </p> <ul>

<li id="GUID-CA623AF7-3752-5369-BFE2-1CDADC963A26"><p> <codeph>URI</codeph>:

the location of the file. </p> </li>

<li id="GUID-9455FFE0-129D-5EDB-B7E9-BC4D907DE53C"><p> <codeph>UniqueId</codeph>:

the content object inside the file. </p> </li>

</ul> <p>A content file is only handled by the agent that recognises it. The

unique identifier is not required to be decoded by anyone other than the agent

that generated it, so the format is left for the agent to implement as it

sees fit. For instance, an OMA DRM agent may put the Content ID (CID) in the <codeph>UniqueId</codeph> field. </p> <p>The

only constraint is that the <codeph>UniqueId</codeph> must be unique within

the file. An application must be able to directly reference a content object

just using the <codeph>UniqueId</codeph>. </p> </section>

<section id="GUID-28BE6074-E800-5320-89DD-D047F5C0FD86"><title>Objects used

to identify a content object within a file</title> <p><b>Virtual path pointer

objects on the stack </b> </p> <p>The <xref href="GUID-0F5CE9B5-E674-3962-8376-CFB1ECB2F601.dita#GUID-0F5CE9B5-E674-3962-8376-CFB1ECB2F601/GUID-70925BDF-36EF-3705-9C95-9EE211543517"><apiname>ContentAccess::TVirtualPathPtr</apiname></xref> is

used to point to two descriptors holding the URI of a file and the <codeph>UniqueId</codeph> of

a content object within the file. It can also be used to point to another <codeph>TVirtualPathPtr</codeph>.

Since it is only a pointer, the original descriptors used to initalise the <codeph>TVirtualPathPtr</codeph> must

not be destroyed or modified while the <codeph>TVirtualPathPtr</codeph> is

still in use. </p> <p><b>Virtual path objects on the heap </b> </p> <p>The <xref href="GUID-0F5CE9B5-E674-3962-8376-CFB1ECB2F601.dita#GUID-0F5CE9B5-E674-3962-8376-CFB1ECB2F601/GUID-D56FD380-1335-33BB-B42E-6C1911274B06"><apiname>ContentAccess::CVirtualPath</apiname></xref> class

stores the file URI and content object <codeph>UniqueId</codeph> in its own

descriptors. There is a cast operator that allows the <codeph>CVirtualPath</codeph> to

be used as if it were a <codeph>TVirtualPathPtr</codeph> . </p> <p><b>Examples </b> </p> <codeblock id="GUID-C2E6E29D-C2DF-5D7C-B262-B979FC91A1A8" xml:space="preserve">// Open a CContent object to browse the objects inside a file 

CContent *c = CContent::NewL(_L("C:\file.dcf")); 

CleanupStack::PushL(c); 

// Create an array to store the embedded objects 

RStreamablePtrArray<CEmbeddedObject> myArray; 

// Get an array of the embedded objects within the current container in the file 

c->GetEmbeddedObjects(myArray); 

// If necessary we can get a "mangled" version of the URI that 

// references the particular object within the file 

// i.e. "C:\file.dcf\\OBJECT1" 

CData* data = iContent->OpenContentL(EPlay,myArray[0]->UniqueId());

TFileName uri;

data->GetStringAttribute(EPreviewURI,uri); 

.

.

.

// Now we can use our TPtrC later to create a TVirtualPath object from a URI 

TVirtualPathPtr aPtr = aURI; 

// print the file URI "C:\file.dcf" 

printf(aPtr.URI()); 

// print the content object's UniqueId "OBJECT1" 

printf(aPtr.UniqueId()); 

// Create a copy of the virtual path on the heap so we don't have any ownership problems 

CVirtualPath *myVirtualpath =  CVirtualPath::NewL(aPtr) 

// Can now delete the CContent object without losing our VirtualPath

CleanupStack::PopAndDestroy(c);</codeblock> </section>

<section><title>Special cases for the UniqueId field</title> <p><b>KNullDesC16()

- "" </b> </p> <p>A zero length <codeph>UniqueId</codeph> is used to refer

to the entire file. If a file is opened this way, no translation of the contents

is performed. The ability to open the file with no translation is required

for example to attach the file to an outgoing message. As with any other function

in CAF, access to the file is at the agent's discretion. </p> <p><b>KDefaultContentObject()

- "DEFAULT" </b> </p> <p>Allows an application to refer to the default content

object within a file. In the case of an unprotected file handled by the <codeph>F32Agent</codeph>,

it is the entire file, the same as if the <codeph>UniqueId</codeph>  <codeph>""</codeph> was

used. Other agents, particularly those with a single content object embedded

within the file, use <codeph>"DEFAULT"</codeph> to refer to their only content

object. </p> <p>Even though the <codeph>DEFAULT</codeph> content object is

supported, it is recommended that agents always use <codeph>CContent</codeph> to

enumerate the objects within the file. </p> </section>