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<task id="GUID-BE65B3A7-04E8-5406-B46A-09E2608E0F1F" xml:lang="en"><title>Requesting

Log Engine Notifications </title><shortdesc>This tutorial describes how to request notification from Log Engine. </shortdesc><prolog><metadata><keywords/></metadata></prolog><taskbody>

<context id="GUID-026E70FC-4181-56D2-810A-F9D70BE9A2E7"><p>The Log Engine

records events so that other applications can react to them in ways which

are not part of its own specification. A typical reaction to an event might

be refreshing the screen of the device or causing it to beep, but that is

not Log Engine functionality. The Log Engine notifies other applications of

a change to its database. It provides two interfaces which you implement to

set up notification of changes: </p> <ul>

<li id="GUID-7CE07F32-E2D1-5E2B-A491-4B3DC5CC5F31"><p> <xref href="GUID-37519930-C95E-3FF1-A32D-D42D0A9E710F.dita"><apiname>MLogClientChangeObserver</apiname></xref>  </p> </li>

<li id="GUID-5D5CFA78-7B04-56CD-B919-D0703F1696EF"><p> <xref href="GUID-7DE036FC-7ECE-38FE-8BC0-7B0CA2B3B195.dita"><apiname>MLogViewChangeObserver</apiname></xref>  </p> </li>

</ul> </context>

<steps id="GUID-5E3B8D4C-C912-5E74-8744-44FE6427754F">

<step id="GUID-81E579ED-7379-5ED9-AAD8-F49A0AE50F06"><cmd>Implement <xref href="GUID-37519930-C95E-3FF1-A32D-D42D0A9E710F.dita"><apiname>MLogClientChangeObserver</apiname></xref>  </cmd>

<info> <xref href="GUID-37519930-C95E-3FF1-A32D-D42D0A9E710F.dita"><apiname>MLogClientChangeObserver</apiname></xref> concerns changes which

are global to the database and it has a single member function to be implemented: </info>

<substeps id="GUID-E55DB2B7-A71E-4EB6-8A69-4F4BB5EABE9B">

<substep id="GUID-E509EE1B-92F6-4C45-BFC6-8370BA3FE4AA"><cmd>Implement <xref href="GUID-539F45CB-1182-38EE-A15C-BCD9093AC24F.dita"><apiname>HandleLogClientChangeEventL</apiname></xref> of <xref href="GUID-37519930-C95E-3FF1-A32D-D42D0A9E710F.dita"><apiname>MLogClientChangeObserver</apiname></xref></cmd>

<info>Its arguments are: </info>

<info><ul>

<li id="GUID-393080A5-BAF1-5461-AF2A-46F413C56383"><p> <xref href="GUID-530281E6-29FC-33F2-BC9B-610FBA389444.dita"><apiname>TUid</apiname></xref> aChangeType

the UID of the type of event which occurred </p> </li>

<li id="GUID-73B0B616-C029-52EF-AF31-53996B639051"><p> <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> aChangeParameter1 </p> </li>

<li id="GUID-34CF35D8-6078-587B-A8C1-00337F5C3C31"><p> <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> aChangeParameter2 </p> </li>

<li id="GUID-800AC30F-DF6F-55CF-9455-D49C25F253D0"><p> <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> aChangeParameter3 </p> </li>

</ul></info>

<info>The last three arguments are context-specific: their meaning is specific

to the type of event that occurred. </info>

</substep>

</substeps>

</step>

<step id="GUID-75C55B15-FA43-5E6D-9967-6B6086BCA32B"><cmd/>

<info>Implement <xref href="GUID-7DE036FC-7ECE-38FE-8BC0-7B0CA2B3B195.dita"><apiname>MLogViewChangeObserver</apiname></xref>  </info>

<info> <xref href="GUID-7DE036FC-7ECE-38FE-8BC0-7B0CA2B3B195.dita"><apiname>MLogViewChangeObserver</apiname></xref> concerns changes which are

specific to a database view and it has three member functions to be implemented: </info>

<substeps id="GUID-5645F222-5B4C-4B28-8AC2-F28256821883">

<substep id="GUID-DB5501DF-E345-426E-B13D-5B3CEF840A28"><cmd/>

<info><xref href="GUID-A41FB471-60EC-3786-8CCC-BD35048ED38A.dita"><apiname>HandleLogViewChangeEventAddedL</apiname></xref></info>

</substep>

<substep id="GUID-D68B3B48-8D28-4086-B5FE-B22D622A741C"><cmd/>

<info><xref href="GUID-D799F87B-C0CE-3129-A526-A3B06469B328.dita"><apiname>HandleLogViewChangeEventChangedL</apiname></xref></info>

</substep>

<substep id="GUID-0698E95C-F370-49B5-B43E-176BF5C5F713"><cmd/>

<info><xref href="GUID-6C1A90CC-BA78-3B37-A39C-DC6D1F714654.dita"><apiname>HandleLogViewChangeEventDeletedL</apiname></xref></info>

</substep>

</substeps>

<info>Each of them has the same arguments: </info>

<substeps id="GUID-368850E6-5B7F-4ADB-99ED-F1843BE1340C">

<substep id="GUID-649209D5-146A-445B-B7FF-E67F061148B8"><cmd/>

<info><xref href="GUID-271367A8-DD4F-3A82-AD88-F3E94F2AA980.dita"><apiname>TLogId</apiname></xref> aId </info>

</substep>

<substep id="GUID-982974D3-2D00-40EB-9A32-1F7588390CAA"><cmd/>

<info><xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> aViewIndex</info>

</substep>

<substep id="GUID-46F2D7CB-5016-4F08-94DA-12BFFDDD535F"><cmd/>

<info><xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> aChangeIndex </info>

</substep>

<substep id="GUID-DF50A88D-DE13-4693-9376-CF6143D8FC7C"><cmd/>

<info><xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> aTotalChangeCount</info>

</substep>

</substeps>

</step>

</steps>

<postreq id="GUID-33582208-BB45-4C81-BF20-886CC5EC7EB7"><p>A change to a view typically occurs as part of a sequence of changes,

and the position of the change event record in the view typically reflects

this

fact. 

</p><p>The argument <codeph>aId</codeph> is the Id of the log event in the database.

The argument <codeph>aViewIndex</codeph> is the position in the view

where the event record was added, changed or deleted. The argument

<codeph>aChangeIndex</codeph> is the index of the event in the sequence of

changes. The argument <codeph>aTotalChangeCount</codeph> is the total number

of events in the sequence of changes  

</p></postreq>

</taskbody><related-links>

<link href="GUID-E4A950EA-5671-5755-B3EF-5D6B90E19AE6.dita"><linktext>Maintaining

Log Events</linktext></link>

<link href="GUID-2022F702-9899-5798-8932-D70119C7177D.dita"><linktext>Setting Up

A Log Engine Client</linktext></link>

<link href="GUID-55ECBCF5-FC29-5A4A-A3C6-1CB1C0D562CE.dita"><linktext>Displaying

Log Events</linktext></link>

<link href="GUID-BCB0E50F-B22E-5964-BB68-BEE1870D9C79.dita"><linktext>Configuring

Log Engine </linktext></link>