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-7250950C-5502-5ACE-864B-0EFD5C253053-GENID-1-8-1-3-1-1-7-1-10-1" xml:lang="en"><title>How |
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13 to create a singleton</title><prolog><metadata><keywords/></metadata></prolog><conbody> |
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14 <p>The <xref href="GUID-F0C084E2-C683-39E2-A131-77FE3206A02C.dita"><apiname>CCoeStatic</apiname></xref> class allows singleton classes to be |
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15 created and stored by the environment (<xref href="GUID-12A9389D-363B-3F54-857F-89EE0EDCDF40.dita"><apiname>CCoeEnv</apiname></xref>) in Thread |
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16 Local Storage (TLS). This provides a means of creating writeable global static |
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17 data. </p> |
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18 <p> <filepath>MySingleton.h</filepath> </p> |
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19 <codeblock id="GUID-B526F5B3-FBC7-5563-8F5C-37B01A0EC28D-GENID-1-8-1-3-1-1-7-1-10-1-2-3" xml:space="preserve"> |
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20 class CMySingleton : public CCoeStatic |
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21 { |
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22 public: |
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23 static CMySingleton* SelfL() ; // Slightly slower |
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24 static CMySingleton* SelfL( CCoeEnv* aCoeEnv ) ; // Slightly faster |
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25 ... |
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26 private: |
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27 CMySingleton() ; |
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28 ~CMySingleton() ; |
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29 } ; |
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30 </codeblock> |
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31 <p> <filepath>MySingleton.cpp</filepath> </p> |
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32 <codeblock id="GUID-FD7053EB-8769-5C04-98E2-3C8EC8589A10-GENID-1-8-1-3-1-1-7-1-10-1-2-5" xml:space="preserve"> |
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33 const TUid KUidMySingleton = {0x10204232} ; |
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34 |
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35 CMySingleton::CMySingleton() : CCoeStatic( KUidMySingleton, CCoeStatic::EThread /*or EApp*/ ) |
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36 { |
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37 } |
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38 |
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39 CMySingleton* CMySingleton::SelfL() |
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40 { |
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41 CMySingleton* self = static_cast<CMySingleton*>( CCoeStatic::Static( KUidMySingleton ) ) ; |
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42 if(!self) |
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43 { |
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44 self = new( ELeave ) CMySingleton() ; |
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45 } |
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46 return self ; |
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47 } |
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48 |
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49 CMySingleton* CMySingleton::SelfL( CCoeEnv* aCoeEnv ) |
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50 { |
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51 CMySingleton* self = static_cast<CMySingleton*>( aCoeEnv->FindStatic( KUidMySingleton ) ) ; |
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52 if( !self ) |
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53 { |
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54 self = new( ELeave ) CMySingleton() ; |
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55 } |
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56 return self ; |
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57 } |
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58 </codeblock> |
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59 <p>A singleton must be given a UID. When it is instantiated for the first |
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60 time the base class constructor adds it to the list of singletons in the environment. |
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61 Any subsequent attempts to instantiate the same singleton will result in a |
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62 panic. </p> |
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63 <p>Singletons may be given a <b>destruction priority</b> and a <b>scope</b>. </p> |
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64 <p>The <b>destruction priority</b> determines when the singleton is destroyed |
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65 relative to any other singletons in the environment's list and relative to |
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66 the App Ui. The default priority, <codeph>EDefaultDestructionPriority</codeph>, |
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67 is 100. The higher the priority, the earlier the singleton will be destroyed. |
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68 A negative value indicates that the singleton should be destroyed after the |
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69 AppUi. The more negative the value, the later the destruction. </p> |
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70 <p>The <b>scope</b> may be <codeph>EThread</codeph> (the default) or <codeph>EApp</codeph> and |
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71 determines the visibility of the singleton. </p> |
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72 <p>Once a singleton has been created it may be accessed through the <xref href="GUID-12A9389D-363B-3F54-857F-89EE0EDCDF40.dita"><apiname>CCoeEnv</apiname></xref> API. </p> |
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73 <codeblock id="GUID-7B6E1AE6-30E6-585C-84AC-5C385F0894D3-GENID-1-8-1-3-1-1-7-1-10-1-2-11" xml:space="preserve">// Singleton access |
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74 IMPORT_C static CCoeStatic* Static( TUid aUid ) ; |
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75 IMPORT_C CCoeStatic* FindStatic( TUid aUid ) ;</codeblock> |
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76 </conbody></concept> |
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