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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept id="GUID-E049772D-A96F-592F-AF59-C9B69E8D24C1-GENID-1-10-1-6-1-1-3-1-10-1" xml:lang="en"><title>Using |
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13 the extended notifier framework</title><prolog><metadata><keywords/></metadata></prolog><conbody> |
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14 <section id="GUID-41892CE3-A4CC-5761-9469-530D6D18EDFE-GENID-1-10-1-6-1-1-3-1-10-1-2-1"><title>The framework</title> <p>Notifiers |
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15 allow components with no direct UI linkage to interact with the user via an |
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16 interface such as a dialog box. For example, a low level component might want |
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17 to warn the user about a low battery level. Typically, such a component would |
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18 not have direct access, or knowledge of, a UI. The solution to this problem |
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19 is provided by what are known as notifiers and the extended notifier framework. |
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20 The UI element (the dialog box) is provided by the device's UI |
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21 through what are known as notifier plug-ins. </p> <p>The extended notifier |
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22 framework is a system that loads these plug-in DLLs from <filepath>Z\sys\bin\notifiers</filepath>. </p> <p>These |
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23 DLLs are expected to export a single factory function at ordinal #1 that returns |
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24 an array of notifiers. A special notifier target type is supported by makmake. |
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25 The second Uid for notifiers should be 0x10005522. </p> <p>The behaviour of |
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26 notifiers is supplied by providing an implementation of the <xref href="GUID-DE445C4B-22EF-3A1F-8A69-57CB703BFAD0.dita"><apiname>MEikSrvNotifierBase2</apiname></xref> interface |
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27 . A notifier is associated with a channel and a priority. Priority is used |
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28 to determine the order of activation if more than one notifier is activated |
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29 at any time. Priority only affects notifiers on the same channel (for example, |
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30 a screen or LED). This means that two notifiers can be active at the same |
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31 time provided that they are on different channels. </p> <p>The channel and |
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32 priority used by all the notifiers in the system needs to be considered carefully |
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33 to avoid them interfering with each other in unexpected ways. The <xref href="GUID-DE445C4B-22EF-3A1F-8A69-57CB703BFAD0.dita"><apiname>MEikSrvNotifierBase2</apiname></xref> derived |
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34 class also needs to be implemented correctly. Notifiers run in the UIKON server |
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35 thread and are accessed on the client side via <xref href="GUID-A6B66713-FECA-3BE7-BB81-1AE5551AD83D.dita"><apiname>RNotifier</apiname></xref>. |
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36 Note that if a notifier panics it will lead to a device reset. </p> </section> |
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37 <section id="GUID-9322CFDB-D07E-54C3-86B1-13BFB082B175-GENID-1-10-1-6-1-1-3-1-10-1-2-2"><title>The factory |
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38 function</title> <p>The factory function at ordinal #1 is expected to return |
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39 an array of notifiers. The following is a typical implementation: </p> <codeblock id="GUID-F5B8C31B-110E-569A-BE9E-3986E94A506D-GENID-1-10-1-6-1-1-3-1-10-1-2-2-3" xml:space="preserve">EXPORT_C CArrayPtr<MEikSrvNotifierBase2>* NotifierArray() |
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40 { |
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41 CArrayPtrFlat<MEikSrvNotifierBase2>* notifiers=new CArrayPtrFlat<MEikSrvNotifierBase2>(5); |
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42 if (notifiers) |
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43 { |
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44 TRAPD(err, CreateNotifiersL(notifiers)); |
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45 if(err) |
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46 { |
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47 TInt count = notifiers->Count(); |
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48 while(count--) |
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49 { |
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50 (*notifiers)[count]->Release(); |
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51 } |
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52 delete notifiers; |
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53 notifiers = NULL; |
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54 } |
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55 } |
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56 return(notifiers); |
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57 } |
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58 </codeblock> <note><p>Ownership of the notifier array or its contents is not |
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59 transferred to the framework until this function returns. To avoid memory |
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60 leaks, all acquired resources must be freed if anything goes wrong part of |
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61 the way through its processing. </p></note> <p>Calling <codeph>Release()</codeph> on |
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62 a notifier should cause that notifier to free all of its resources, and as |
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63 a minimum should call <codeph>delete this;</codeph>. See <xref href="GUID-DE445C4B-22EF-3A1F-8A69-57CB703BFAD0.dita#GUID-DE445C4B-22EF-3A1F-8A69-57CB703BFAD0/GUID-CF772B65-7D65-3ADC-B566-9ED2A263942F"><apiname>MEikSrvNotifierBase2::Release()</apiname></xref>. </p> <p>Returning |
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64 a <codeph>Null</codeph> value from this function causes the framework to leave |
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65 with <xref href="GUID-64F6761A-4716-37C3-8984-FF18FC8B7B7D.dita"><apiname>KErrNoMemory</apiname></xref>. </p> <p>The <codeph>CreateNotifiersL()</codeph> function |
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66 should be implemented as follows: </p> <codeblock id="GUID-15535A2D-A1F3-5A18-99B7-B2973BDFB255-GENID-1-10-1-6-1-1-3-1-10-1-2-2-8" xml:space="preserve">LOCAL_C void CreateNotifiersL(CArrayPtrFlat<MEikSrvNotifierBase2>* aNotifiers) |
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67 { |
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68 MEikSrvNotifierBase2* notifier; |
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69 notifier = CMyNotifierA::NewL(); |
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70 CleanupStack::PushL(notifier); |
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71 aNotifiers->AppendL(notifier); |
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72 CleanupStack::Pop(notifier); |
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73 ... |
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74 ... |
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75 // typically, repeat this procedure for as |
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76 // many notifiers as are implemented |
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77 // in the plug-in DLL. |
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78 }</codeblock> <note><p>Use of the standard Symbian platform technique |
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79 of using the cleanup stack to hold pointers to allocated objects for as long |
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80 as these objects have no owner; this prevents memory leaks. For this reason, |
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81 avoid using a technique such as <codeph>aNotifiers->AppendL(CMyNotifierA::NewL());</codeph>, |
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82 which, although shorter, will result in a memory leak if the <codeph>AppendL()</codeph> operation |
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83 fails. </p></note> </section> |
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84 </conbody></concept> |