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85 lines
3.4 KiB
85 lines
3.4 KiB
15 years ago
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How to implement DCOP communication between two applications so that
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1) it works when the applications are standalone (separate processes)
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2) it works when the applications are loaded as parts, embedded into kontact
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3) it behaves properly when a separate process exits/crashes.
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In the part
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===========
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Let's say that part 'A' wants to use the interface "Foo", via DCOP.
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(where Foo is usually a generic name, e.g. Calendar, Mailer, AlarmDaemon, etc.)
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The services which implement this interface are associated with the service type
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"DCOP/Foo".
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One of those services is application 'B', which implements "Foo" - note that
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'B' should make sure that the "Foo" DCOP interface is available both when
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'B' is used as standalone process and when 'B' is only loaded as a part.
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(This means that if the app doesn't use its own part, then both should implement
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"Foo", like kaddressbook does. Of course it's simpler if the app uses its own part :)
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Here are some code snippets that must go into the part (A) that wants to use "Foo":
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* Constructor:
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m_foo_stub = 0L;
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kapp->dcopClient()->setNotifications( true );
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connect( kapp->dcopClient(), SIGNAL( applicationRemoved( const QCString&)),
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this, SLOT( unregisteredFromDCOP( const QCString& )) );
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* Destructor:
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kapp->dcopClient()->setNotifications( false );
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delete m_foo_stub;
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[Note that setNotifications() is implemented with a refcount, this is the
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correct way to do it and it won't mess up other parts]
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* bool connectToFoo() method, which uses KDCOPServiceStarter::self()->findServiceFor("DCOP/Foo").
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See test part for details (plugins/test/test_part.cpp).
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* unregisteredFromDCOP( const QCString& appId ) slot, which will be called when
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the process implementing Foo exits. The method simply does:
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if ( m_foo_stub && m_foo_stub->app() == appId )
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{
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delete m_foo_stub;
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m_foo_stub = 0;
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}
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* Now you can finally use the foo dcop interface. First you need to connect
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to it:
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if ( !connectToFoo() )
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return;
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Then you can use m_foo_stub to call the DCOP methods.
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In case of critical methods, where you want to make 100% sure that the DCOP
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call was correctly done (e.g. the remote app didn't crash during the call),
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you can use if ( !m_foo_stub->ok() ).
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In the kontact plugin
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=====================
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* Don't use dcopClient() until the part is loaded
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* After loading the part, you might want to create a DCOP stub to use some
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of its methods (do both in a loadPart() method, e.g.).
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* Implement createDCOPInterface( const QString& serviceType ), to
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load the part if the serviceType is one provided by it.
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See KAddressbookPlugin (plugins/kaddressbook/*) for a working example.
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Don't forget to
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===============
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* Define the service type, using a "Type=ServiceType" .desktop file,
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with "X-KDE-ServiceType=DCOP/Foo".
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See e.g. kdepim/kaddressbook/dcopaddressbook.desktop
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* Add DCOP/Foo to the application's ServiceTypes list, in its .desktop file
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See e.g. kdepim/kaddressbook/kaddressbook.desktop
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* Make sure that X-DCOP-ServiceType and X-DCOP-ServiceName are specified too.
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Designing DCOP interfaces
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=========================
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Porting the kroupware signals/slots to DCOP requires some changes.
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For instance any non-const reference (such as those used for returning
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values to the caller) has to be changed. If there is more than one
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value to be returned, you need to
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* define a structure containing all the returned values
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* define QDataStream << and >> operators for that structure.
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$Id$
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