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<concept xml:lang="en" id="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C"><title>Location Settings API</title><shortdesc>The Location Settings API allows an application to get and set the properties of a PSY. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody><p> </p> <section><title>Contents</title> <ul><li id="GUID-5C7D32AA-BBA2-55EF-BA32-5F2D461EAFC0"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-1122A71A-7868-5394-917B-5C5EB8E97EC8">Purpose</xref>  </p> </li> <li id="GUID-FD73A08E-C032-5A49-8F95-CBF9DBF567A5"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-B6F9AB52-9375-5601-8760-1C3B72620E71">API description</xref>  </p> <ul><li id="GUID-4E424394-F32F-594F-BD79-3BF54E292793"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-A45324D8-CF2A-52BD-A08F-7C3A56A8E9F8">PSY attributes</xref>  </p> </li> </ul> </li> <li id="GUID-81B5646F-4EAA-5869-95BC-95832CC798B0"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-5A9DAD33-86D7-5066-9CED-36FEF03AEC80">API summary</xref>  </p> </li> <li id="GUID-E599DD05-DA59-5CD2-A7B7-C4B46AABE1D0"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-F2BD6C21-25D7-5E3A-B24E-16D783EDDFA6">Using the API</xref>  </p> <ul><li id="GUID-12DF3B2A-93B7-5F5D-8330-E7A25822B71C"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-54DC1DC0-290A-55DD-B5BD-D87BE8E3194F"> Retrieving information about installed PSYs</xref>  </p> </li> <li id="GUID-90FA746B-3BAA-542F-9B3A-9888D8BC28EC"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-B5AC0535-5CFA-5A5F-A67F-F05A3D7F78D1">Modifying PSY attributes</xref>  </p> </li> <li id="GUID-0B6F5C23-8D8B-5879-B91B-7D0793A1323B"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-0ADE50DD-84E3-5DAE-94E3-4BB424665734">Changing priority order of PSYs </xref>  </p> </li> <li id="GUID-763E86DE-BBBD-567A-8F54-C2A521402CDE"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-1438A703-4F6F-5AC2-A52C-37BABE7AF5B9"> Listening to settings change events </xref>  </p> </li> </ul> </li> <li id="GUID-56AF88DC-075C-5A2B-BE22-6F0450E19537"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-1EBC1700-209D-5AC2-ABF7-CB866A8728C8">Error handling</xref>  </p> </li> <li id="GUID-F7769CE9-B43F-5578-A67D-B9C5C98DDFAD"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-5523F46D-5CDA-5E85-B4B8-193FD8B26E32">Memory overhead</xref>  </p> </li> <li id="GUID-9455497D-1F38-5123-AFAB-239DDC553C12"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-FFEA130F-33FE-5E8D-AAE2-9AD8DF68DADE">See also</xref>  </p> </li> </ul> </section> <section id="GUID-1122A71A-7868-5394-917B-5C5EB8E97EC8"><title>Purpose</title> <p>The Location Settings API is an interface for managing the settings of the Location Framework and of Positioning Plug-ins (PSYs). The settings consist of the relative priorities of PSYs installed on the mobile device and modifiable and read-only attributes of PSYs. </p> </section> <section id="GUID-B6F9AB52-9375-5601-8760-1C3B72620E71"><title>API description</title> <p>This API is intended for use by a system application (such as a settings UI) that allows the user of a phone to view and edit settings that affect the behaviour of the Location Framework. The API allows a user to manage the priority ordering of PSYs and to access their modifiable and non-modifiable attributes </p> <p>The priority ordering of PSYs is used when a client of the <xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref> uses the <xref href="GUID-1EAEB7EF-0AC7-37C7-B35F-C9B780FFC575.dita"><apiname>RPositioner</apiname></xref> class without specifying particular positioning module ID (by calling <xref href="GUID-1EAEB7EF-0AC7-37C7-B35F-C9B780FFC575.dita#GUID-1EAEB7EF-0AC7-37C7-B35F-C9B780FFC575/GUID-AF3D9B5F-8025-3AFF-A101-82025520EBD6"><apiname>RPositioner::Open()</apiname></xref> without parameters). The Location Server uses the PSY with the highest priority if possible and falls back to next one in the priority list in case of failure. </p> <p id="GUID-A45324D8-CF2A-52BD-A08F-7C3A56A8E9F8"><b>PSY attributes</b> </p> <p>PSY attributes can be grouped by type: </p> <dl><dlentry><dt>Non-modifiable attributes</dt> <dd><p>These properties include a descriptive name, UID, positioning plug-in version, positioning technology, capabilities, time to first fix, positioning accuracy, power consumption etc. </p> <p>For more information about non-modifiable attributes see <xref href="GUID-DA2DC704-CE65-54FB-9049-4E1C73092EDF-GENID-1-12-1-19-1-1-10-1-5-1-5-1-8-1.dita">Positioning Plug-in Information API</xref>. </p> <p>Non-modifiable attributes are read from each PSY's repository file,. The PSY name is read from a resource file, which should be referenced by the repository file. If the resource file is not referenced in the repository file then the PSY name is taken from ECOM attributes of the PSY plug-in (which means that the name cannot be localized). </p> </dd> </dlentry> <dlentry><dt>Modifiable attributes</dt> <dd><p>These attributes include the availability status of the PSY (enabled or disabled), the cost of using the PSY and its visibility. </p> <p>Modifiable attributes are stored in the Central Repository. </p> <p>Table 1 describes the modifiable PSY attributes: </p> <table id="GUID-7330D155-DBE5-57C5-B6A6-B4AD5855ECBC"><tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/><thead><row><entry>Attribute</entry> <entry>Description</entry> </row> </thead> <tbody><row><entry><p>Cost </p> </entry> <entry><p>User-defined runtime setting for the cost of using a specific positioning technology. Possible values are defined by <xref href="GUID-1AA235FA-CEC1-3853-8F96-C538C02B596D.dita#GUID-1AA235FA-CEC1-3853-8F96-C538C02B596D/GUID-78C084A0-43F8-3040-BD98-70E2E62A5D45"><apiname>TPositionQuality::TCostIndicator</apiname></xref> from <xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref>. </p> <p>The cost attribute is modifiable because in some cases the cost of using a PSY can be dependent on the user’s subscription model. </p> </entry> </row> <row><entry><p>Availability </p> </entry> <entry><p>Determines whether a PSY is enabled to be used through <xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref> (<xref href="GUID-1EAEB7EF-0AC7-37C7-B35F-C9B780FFC575.dita"><apiname>RPositioner</apiname></xref>) or not. </p> </entry> </row> <row><entry><p>Visibility </p> </entry> <entry><p>Determines whether a PSY needs to be listed by the <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita"><apiname>CPosModules</apiname></xref> class of this API. </p> </entry> </row> </tbody> </tgroup> </table> <p>Table 1. Modifiable PSY attributes. </p> </dd> </dlentry> <dlentry><dt>Positioning plug-in specific settings</dt> <dd><p>Each PSY can have any number of attributes that are specific for the positioning technology it encapsulates (for example, baud rate for external GPS). The Location Settings API does not provide access to these settings. </p> </dd> </dlentry> </dl> </section> <section id="GUID-5A9DAD33-86D7-5066-9CED-36FEF03AEC80"><title>API summary</title> <p>Figure 1 shows public classes of the Location Settings API. </p> <fig id="GUID-9F8E279C-A702-5557-A2CE-FD085EF15E4C"><title>
             Figure 1. Location Settings API class diagram 
          </title> <image href="GUID-E3F116C0-F133-5008-BD7A-421D66FB6588_d0e448480_href.png" placement="inline"/></fig> <p>Table 1 lists the classes and types of the API. </p> <table id="GUID-404231E8-601E-5D56-A3E2-D6DFFB266AC7"><tgroup cols="3"><colspec colname="col0"/><colspec colname="col1"/><colspec colname="col2"/><thead><row><entry>Class Name</entry> <entry>Description</entry> <entry>Header file</entry> </row> </thead> <tbody><row><entry><p> <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita"><apiname>CPosModules</apiname></xref>  </p> </entry> <entry><p>The main class of the Location Settings API. It is used for accessing PSY attributes and managing priority list of PSYs. A client can also register to listen for changes in the settings. </p> </entry> <entry><p> <codeph>EPos_CPosModuleIdList.h</codeph>  </p> </entry> </row> <row><entry><p> <xref href="GUID-1AB3C182-B9F9-3C75-9FC2-C550500046CB.dita"><apiname>CPosModuleUpdate</apiname></xref>  </p> </entry> <entry><p>Represents an update of the modifiable attributes of a PSY. An update is committed by calling <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-590B754B-2ECB-313F-A8C5-44B2C2A1E37F"><apiname>CPosModules::UpdateModuleL()</apiname></xref>. </p> </entry> <entry><p> <codeph>EPos_CPosModuleUpdate.h</codeph>  </p> </entry> </row> <row><entry><p> <xref href="GUID-2E3EB368-F820-3B1F-A025-939D78A5F9CE.dita"><apiname>CPosModuleIdList</apiname></xref>  </p> </entry> <entry><p>Represents a list of PSY IDs. Used to get and set the priority list of PSYs. It contains methods for appending, inserting, removing and finding PSY IDs in the list. </p> </entry> <entry><p> <codeph>EPos_CPosModuleIdList.h</codeph>  </p> </entry> </row> <row><entry><p> <xref href="GUID-2C027B56-CC69-307E-ABB4-BBB532D8F473.dita"><apiname>MPosModulesObserver</apiname></xref>  </p> </entry> <entry><p>The interface that is implemented by clients in order to receive notifications of changes in the PSY settings. A client subscribes for notifications through the <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita"><apiname>CPosModules</apiname></xref> class. </p> <p>Notification event information is given in a <xref href="GUID-5760EA9E-7720-31CD-B8F7-29370E2B6FCB.dita"><apiname>TPosModulesEvent</apiname></xref> structure. </p> <p>Typedef <xref href="GUID-9559BB6D-894E-3814-8D60-4102A465EC3D.dita"><apiname>TPosModulesEventType</apiname></xref> defines possible event types. </p> </entry> <entry><p> <codeph>EPos_MPosModulesObserver.h</codeph>  </p> </entry> </row> </tbody> </tgroup> </table> <p>Table 1. Classes and types of the Location Settings API. </p> <p><b>Libraries </b> </p> <p>API classes are packaged in <filepath>eposmodset.dll</filepath>. Clients link with <filepath>eposmodset.lib</filepath>. </p> <p><b>Capabilities </b> </p> <p>API clients require <codeph>WriteDeviceData</codeph> capability to update modifiable settings (PSY priority order, modifiable PSY attributes). </p> <p>API clients require no capabilities to read PSY settings. </p> </section> <section id="GUID-F2BD6C21-25D7-5E3A-B24E-16D783EDDFA6"><title>Using the API</title> <p>Uses cases for the API are: </p> <ul><li id="GUID-299D0BA9-6630-5D30-9533-989BCED32F68"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-54DC1DC0-290A-55DD-B5BD-D87BE8E3194F"> Retrieving information about installed PSYs</xref>  </p> </li> <li id="GUID-26BEDF7C-3354-57F2-AC90-FEAD79E7C5A3"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-B5AC0535-5CFA-5A5F-A67F-F05A3D7F78D1">Modifying PSY attributes</xref>  </p> </li> <li id="GUID-8023AF65-8962-59D4-889E-440CF4C11677"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-0ADE50DD-84E3-5DAE-94E3-4BB424665734">Changing priority order of PSYs </xref>  </p> </li> <li id="GUID-EFAF4AE9-5845-5882-88BC-B1B6A209324F"><p><xref href="GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C.dita#GUID-DABBFC53-CC93-54AA-ADFD-6756B1EA878C/GUID-1438A703-4F6F-5AC2-A52C-37BABE7AF5B9"> Listening to settings change events </xref>  </p> </li> </ul> <p id="GUID-54DC1DC0-290A-55DD-B5BD-D87BE8E3194F"><b>Retrieving information about installed PSYs </b> </p> <p>A client can read ordered list of PSYs by using <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-5A626C61-0A95-3628-9CBB-FDBF04676281"><apiname>CPosModules::ModuleIdListL()</apiname></xref> or <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-6A8BBAA1-3938-3572-BA4E-B7C9F8BCA82E"><apiname>CPosModules::ModuleIdListLC()</apiname></xref>. These methods return a list of IDs for the currently installed PSYs in priority order. Only the PSYs which have visibility attribute set to 1 (ETrue) are listed. </p> <p>The client may request information from a specific PSY by providing its ID to <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-66188192-A70D-3CF4-B35F-50BEBE8431C4"><apiname>CPosModules::GetModuleInfoL()</apiname></xref>. If a PSY with the specified ID is found in the system, its data is returned in the <xref href="GUID-1E6620E4-F194-3482-BBD1-D85F3528D87D.dita"><apiname>TPositionModuleInfoBase</apiname></xref> derived object, supplied by client. Currently, the only supported subclass is <xref href="GUID-B098F3DB-E2FE-3C5A-8508-4B04D954AB26.dita"><apiname>TPositionModuleInfo</apiname></xref>. For more information, see <xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref>. </p> <p>Figure 2 shows the client listing all available PSYs and retrieving their attributes: </p> <fig id="GUID-3C2F95B1-7F68-59B0-A1F9-8562432D43FD"><title>
                Figure 2. Retrieving PSY information 
             </title> <image href="GUID-E35C440C-4191-510A-AD33-2CF56E41EDD2_d0e448735_href.png" placement="inline"/></fig> <p>The following example shows the client getting list of names of enabled plug-ins: </p> <codeblock id="GUID-C82837F0-D44E-5046-84F6-DA74123F39B7" xml:space="preserve">void ListEnabledPluginsL( CDesCArray&amp; aNames )
{
// Open the storage
CPosModules* db = CPosModules::OpenL();
CleanupStack::PushL( db );

// List entries
CPosModuleIdList* idList = db-&gt;ModuleIdListLC();

// Get the display name and status of each installed positioning plug-in
for (TInt I = 0; I &lt; idList-&gt;Count(); I++)
    {
    // get PSY info
    TPositionModuleInfo moduleInfo;
    db-&gt;GetModuleInfoL( (*idList)[I], moduleInfo );

    if ( moduleInfo.IsAvailable() )
        {
        // read PSY’s name
        TBuf&lt;KPositionMaxModuleName&gt; moduleName;
        moduleInfo.GetModuleName( moduleName );
        aNames.AppendL( moduleName );
        }
    }

CleanupStack::PopAndDestroy( idList );
CleanupStack::PopAndDestroy( db );
}
</codeblock> <p id="GUID-B5AC0535-5CFA-5A5F-A67F-F05A3D7F78D1"><b>Modifying PSY attributes</b> </p> <p>In order to modify PSY attributes, the client sets values in a <xref href="GUID-1AB3C182-B9F9-3C75-9FC2-C550500046CB.dita"><apiname>CPosModuleUpdate</apiname></xref> object and sends it to <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-590B754B-2ECB-313F-A8C5-44B2C2A1E37F"><apiname>CPosModules::UpdateModuleL()</apiname></xref>. The <xref href="GUID-1AB3C182-B9F9-3C75-9FC2-C550500046CB.dita"><apiname>CPosModuleUpdate</apiname></xref> class allows a client to change the cost, availability, and visibility attributes of a PSY. </p> <p>Figure 3 shows the steps to change the modifiable attributes of PSY. </p> <fig id="GUID-FBD28CD7-609C-53C5-8931-1BA156D89ADF"><title>
                Figure 3. Modifying PSY attributes 
             </title> <image href="GUID-2051AAEF-140C-5EEF-874F-52971E76F853_d0e448770_href.png" placement="inline"/></fig> <p><b>PSY visibility and availability </b> </p> <p> <b/>The visibility attribute only defines whether a PSY is listed when a client asks for a list of all available PSYs. Turning this attribute off for a specific PSY does not prevents client applications (which know its module ID) from using this PSY through <xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref>. The client can still specify PSY’s module ID as a parameter for <xref href="GUID-1EAEB7EF-0AC7-37C7-B35F-C9B780FFC575.dita#GUID-1EAEB7EF-0AC7-37C7-B35F-C9B780FFC575/GUID-AF3D9B5F-8025-3AFF-A101-82025520EBD6"><apiname>RPositioner::Open()</apiname></xref> and connection to that PSY is granted. </p> <p>The availability attribute defines if a PSY is totally hidden from the system and its use through the <xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref> is disabled. </p> <p>The following code example shows how to hide the PSY from the PSY list and prevent its use: </p> <codeblock id="GUID-09028885-AF82-5EA0-9F20-EBB64B0821C0" xml:space="preserve">// Open the storage
CPosModules* db = CPosModules::OpenL();
CleanupStack::PushL( db );

// Assuming the positioning plug-in UID is known
const TPositionModuleId id = {0x12345678};

// Disable the PSY and hide it from the list
CPosModuleUpdate* updateParams = CPosModuleUpdate::NewLC();
updateParams-&gt;SetUpdateAvailability( EFalse );
updateParams-&gt;SetUpdateVisibility( EFalse );

// Commit changes
db-&gt;UpdateModuleL( id, *updateParams );

CleanupStack::PopAndDestroy( updateParams );
CleanupStack::PopAndDestroy( db );
</codeblock> <p id="GUID-0ADE50DD-84E3-5DAE-94E3-4BB424665734"><b>Changing the priority order of PSYs</b> </p> <p>The client application can retrieve and change the priority order of installed PSYs using methods from the <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita"><apiname>CPosModules</apiname></xref> class. The priority of a single PSY is retrieved using <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-6C96F839-A1C4-3A20-8A6D-833300DDE0D6"><apiname>CPosModules::PriorityL()</apiname></xref>. The whole priority list is returned by <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-5A626C61-0A95-3628-9CBB-FDBF04676281"><apiname>CPosModules::ModuleIdListL()</apiname></xref>. </p> <p>There are several methods to change positioning plug-in priorities: </p> <ul><li id="GUID-972EC3C6-951C-592E-8391-CB68417AD739"><p> <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-5B24CF77-0867-35E8-BD83-7012BE62BDBE"><apiname>CPosModules::SetModulePriorityL()</apiname></xref> <codeph/>(two variants) allows a client to change priority of a single PSY. A change to one PSY can affect the priorities of other PSYs. </p> </li> <li id="GUID-01B1423E-BFD2-5F34-A465-351559E62083"><p> <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-349B5FFC-4BEE-3C90-9909-3B24947C5923"><apiname>CPosModules::SetModulePrioritiesL()</apiname></xref> allows a client to specify the required order of all the PSYs at the same time. </p> </li> </ul> <p>The following example code demonstrates how a client can upgrade a PSY to the highest priority. </p> <codeblock id="GUID-4F58DDAB-8171-5812-8E22-5D6630247FAE" xml:space="preserve">void MakePluginTopmostPriorityL( TPositionModuleId aModuleId )
{
// Open the storage
CPosModules* db = CPosModules::OpenL();
CleanupStack::PushL( db );

const TInt KTopMostPriority = 0;
db-&gt;SetModulePriorityL( aModuleId, KTopMostPriority );

CleanupStack::PopAndDestroy( updateParams );
CleanupStack::PopAndDestroy( db );
}</codeblock> <p> <codeph>CPosModules::SetModulePrioritiesL()</codeph> allows a client to set the order of all PSYs immediately by supplying a list of plug-in IDs in the required order. Note that <b>all</b> the visible plug-ins must be declared in the supplied list: it is required that the list contains the same set of PSY IDs as it would be returned by <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-5A626C61-0A95-3628-9CBB-FDBF04676281"><apiname>CPosModules::ModuleIdListL()</apiname></xref>. </p> <p> <b>Note: </b> Invisible PSYs are not ordered, i.e. they do not have any priority. When an invisible PSY is made visible, it will be assigned a priority according to its preference (defined in <xref href="GUID-DA2DC704-CE65-54FB-9049-4E1C73092EDF-GENID-1-12-1-19-1-1-10-1-5-1-5-1-8-1.dita">Positioning Plug-In Information API</xref>) and an internal sorting algorithm of the Location Framework. </p> <p>The following example shows how the client could move a PSY to the first place in priority order by specifying a whole new priority list: </p> <codeblock id="GUID-129B4AE4-B6A0-56AF-B7EB-3C97C23C21EB" xml:space="preserve">void MakePluginTopmostPriority2L( TPositionModuleId aModuleId )
{
// Open the storage
CPosModules* db = CPosModules::OpenL();
CleanupStack::PushL( db );

// Get current list first
CPosModuleIdList* idList = db-&gt;ModuleIdListLC();
TInt currentPriority = idList-&gt;Find( aModuleId );
idList-&gt;MoveL( currentPriority, 0 );

// Save new order
db-&gt;SetModulePrioritiesL( *idList );

CleanupStack::PopAndDestroy( idList );
CleanupStack::PopAndDestroy( db );
}</codeblock> <p id="GUID-1438A703-4F6F-5AC2-A52C-37BABE7AF5B9"><b>Listening to settings change events</b> </p> <p>A client can register an observer to listen for changes in the location settings. The observer is notified when any change occurs. The observer is set by calling <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-A13A64E1-565A-3ECB-B968-245EEFFC575A"><apiname>CPosModules::SetObserverL()</apiname></xref>. The observer must implement the <xref href="GUID-2C027B56-CC69-307E-ABB4-BBB532D8F473.dita"><apiname>MPosModulesObserver</apiname></xref> interface to receive settings change notifications. The observer can be removed by calling <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-B2C15AE8-5073-3992-82F1-73800447C067"><apiname>CPosModules::RemoveObserver()</apiname></xref>. </p> <p>The event information is defined by <xref href="GUID-5760EA9E-7720-31CD-B8F7-29370E2B6FCB.dita"><apiname>TPosModulesEvent</apiname></xref> <codeph/>, which contains the ID of the affected module (if the event is associated with a single module) and type of the event. Event types are defined by <xref href="GUID-9559BB6D-894E-3814-8D60-4102A465EC3D.dita"><apiname>TPosModulesEventType</apiname></xref>. </p> <p> <b>Note</b>: Events are reported as detected by comparing current global settings with their local copy created for the observer. This copy is created when event observer is set by <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-A13A64E1-565A-3ECB-B968-245EEFFC575A"><apiname>CPosModules::SetObserverL()</apiname></xref>. It is updated whenever changes are detected. This means that no events will be reported to the observer if no changes have happened since the observer was set. </p> <p>Many events imply changes in priority order. If the client is interested in priority order it should reload the list of PSYs by calling <xref href="GUID-3EC269A3-61A0-378B-A909-AB5881E47769.dita#GUID-3EC269A3-61A0-378B-A909-AB5881E47769/GUID-5A626C61-0A95-3628-9CBB-FDBF04676281"><apiname>CPosModules::ModuleIdListL()</apiname></xref> whenever such an event is reported. </p> <p>Table 2 describes possible events. </p> <table id="GUID-4B70F09F-2ECA-50F3-AC15-E1BC6CA1FD55"><tgroup cols="3"><colspec colname="col0"/><colspec colname="col1"/><colspec colname="col2"/><thead><row><entry>Event type _TPosModulesEventType</entry> <entry>Is module ID set in TPosModulesEvent object ?</entry> <entry>Description</entry> </row> </thead> <tbody><row><entry><p> <codeph>EPosModulesEventUnspecified</codeph>  </p> </entry> <entry><p>No </p> </entry> <entry><p>Many changes in settings are detected, which affect priority order and PSY attributes. The client should reload the priority list and PSYs attributes. </p> </entry> </row> <row><entry><p> <codeph>EPosModulesEventModuleInstalled</codeph>  </p> </entry> <entry><p>Yes </p> </entry> <entry><p>New PSY is installed and priority list is updated accordingly. The client can get PSYs attributes. </p> </entry> </row> <row><entry><p> <codeph>EPosModulesEventModuleRemoved</codeph>  </p> </entry> <entry><p>Yes </p> </entry> <entry><p>A PSY is uninstalled and the priority list is updated accordingly. The client can no longer use the PSY. </p> </entry> </row> <row><entry><p> <codeph>EPosModulesEventPrioritiesChanged</codeph>  </p> </entry> <entry><p>No </p> </entry> <entry><p>Changes in PSY priority order have occurred (PSYs reordered). No PSY attributes have changed. </p> </entry> </row> <row><entry><p> <codeph>EPosModulesEventCostChanged</codeph>  </p> </entry> <entry><p>Yes </p> </entry> <entry><p>The cost indicator of a PSY has been changed. </p> </entry> </row> <row><entry><p> <codeph>EPosModulesEventAvailabilityChanged</codeph>  </p> </entry> <entry><p>Yes </p> </entry> <entry><p>The availability status of a PSY has been changed. </p> </entry> </row> <row><entry><p> <codeph>EPosModulesEventVisibilityChanged</codeph>  </p> </entry> <entry><p>Yes </p> </entry> <entry><p>The visibility status of a PSY has been changed and priority list is updated accordingly. </p> </entry> </row> </tbody> </tgroup> </table> <p>Table 2. Settings event types and their meaning. </p> <p>Figure 4 shows basic steps that a client takes to listen for changes in location settings: </p> <fig id="GUID-2EC64C4D-D776-5F71-9B87-0A368C7872EF"><title>
                Figure 4. Listening to change events 
             </title> <image href="GUID-450554F3-BA17-5C89-9E01-C0AFD4AC9638_d0e449105_href.png" placement="inline"/></fig> <p>This example shows how a client can listen for PSY events: </p> <codeblock id="GUID-43D1A5C0-659D-517C-BE4B-132BD8FB9087" xml:space="preserve">class CModuleEventListener : public CBase, public MPosModulesObserver
    {
    public:
        CModuleEventListener( CPosModules&amp; aSettings );
        // Starts observing change events
        void StartObservingL();
        // Stops observing change events
        void StopObservingL();

    public: // from MPosModulesObserver
        void HandleSettingsChangeL( TPosModulesEvent aEvent );
        ...

    private:
        CPosModules&amp; iSettings;
    };

// Constructor stores reference to CPosModules
CModuleEventListener::CModuleEventListener( CPosModules&amp; aSettings )
: iSettings( aSettings )
    {
    }

void CMyEventListener::StartObservingL()
    {
    iSettings.SetObserverL( *this );
    }

void CMyEventListener::StopObserving()
    {
    iSettings.RemoveObserver();
    }

// Called whenever change in location settings is detected
void CMyEventListener::HandleSettingsChangeL( TPosModulesEvent aEvent )
    {
    switch ( aEvent.iType )
        {
        case EPosModulesEventModuleInstalled:
            // new PSY installed, add to UI
            break;
        case EPosModulesEventModuleRemoved:
            // remove PSY from UI
            break;
        case EPosModulesEventPrioritiesChanged:
            // reload PSY list and update UI
            break;
        case EPosModulesEventCostChanged:
            // check new state and update UI, if needed
            break;
        case EPosModulesEventAvailabilityChanged:
            // check new state and update UI, if needed
            break;
        case EPosModulesEventVisibilityChanged:
            // check new state and update UI, as needed
            break;
        case EPosModulesEventUnspecified:
        default:
            // reload PSY list and update UI, many changes happened
            break;
        }
    }
</codeblock> <p> </p> </section> <section id="GUID-1EBC1700-209D-5AC2-ABF7-CB866A8728C8"><title>Error handling</title> <p>Accessing location settings can fail with error code <codeph>KErrLocked</codeph>. Read operations fail if some other client is modifying the settings at the same time. Writing operation fails if any other client is reading settings at the same time. The client should retry the failed operation. </p> <p>The interface uses the system-wide error codes of the Symbian platform and defines its own panic codes, defined in following table. A panic is used to detect programming errors. Panic category is <codeph>LocationSettings</codeph>. </p> <table id="GUID-A5B764CD-00BE-561D-A8B6-019BE20D69DE"><tgroup cols="3"><colspec colname="col0"/><colspec colname="col1"/><colspec colname="col2"/><thead><row><entry>Panic code</entry> <entry>Panic name</entry> <entry>Description</entry> </row> </thead> <tbody><row><entry><p>0</p> </entry> <entry><p> <codeph>EPosLocSetPanicParameterOutOfRange</codeph>  </p> </entry> <entry><p>An invalid value has been passed to a function. </p> </entry> </row> <row><entry><p>1</p> </entry> <entry><p> <codeph>EPosLocSetPanicObserverIsAlreadySet</codeph>  </p> </entry> <entry><p>The client tried to set an observer in CPosModules even though an observer had already been set. <codeph>CPosModules::RemoveObserver()</codeph> must be called before the new observer is set. </p> </entry> </row> <row><entry><p>2</p> </entry> <entry><p> <codeph>EPosLocSetPanicObserverNotStopped</codeph>  </p> </entry> <entry><p>The client tries to destroy CPosModules while the observer is still set. </p> </entry> </row> </tbody> </tgroup> </table> </section> <section id="GUID-5523F46D-5CDA-5E85-B4B8-193FD8B26E32"><title>Memory overhead</title> <p>Over the cost of allocating API classes, the only additional memory required is used by the API for its internal cache of PSY attributes. This is less than 200 bytes per installed PSY. </p> </section> <section id="GUID-FFEA130F-33FE-5E8D-AAE2-9AD8DF68DADE"><title>See also</title> <p><xref href="GUID-D0318BB6-0B9F-5A1C-AB0B-61BA22D28661.dita">Location Acquisition API</xref>  </p> </section> </conbody></concept>