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Thread: Multiple instance of Plugin object

  1. #1
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    Default Multiple instance of Plugin object

    Hi,

    can I instantiate multiple object of a plugin class?
    I show you a prototype of code I'd like to use

    Qt Code:
    1. QPluginLoader loader (pluginDir.absoluteFilePath (fileName));
    2.  
    3. QObject *instance = loader.instance ();
    4. QObject *newObj = 0;
    5. QMetaObject *mo = 0;
    6. if (instance) {
    7. IExample *plugin = qobject_cast<IExample*>(instance);
    8. if (plugin) {
    9. qDebug() << instance->metaObject ()->className () << "plugin says:"
    10. << plugin->messageString ();
    11.  
    12. newObj = instance->metaObject ()->newInstance (0);
    13. if (0 != newObj)
    14. qDebug () << "Create New Instance OK";
    15. else
    16. qDebug () << "Create New Instance Failed";
    17. }
    18. }
    To copy to clipboard, switch view to plain text mode 

    where IExample is defined

    Qt Code:
    1. class IExample
    2. {
    3. public:
    4. virtual ~IExample () {}
    5.  
    6. virtual QString messageString () const = 0;
    7. };
    8.  
    9. Q_DECLARE_INTERFACE (IExample, "local.costa.IExample/1.0")
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    and this is the loaded plugin

    Qt Code:
    1. class HelloWorldPlugin: public QObject, IExample
    2. {
    3. Q_OBJECT
    4. Q_INTERFACES (IExample)
    5.  
    6. public:
    7. HelloWorldPlugin(QObject *parent = 0);
    8.  
    9. QString messageString () const;
    10. };
    To copy to clipboard, switch view to plain text mode 

    Qt Code:
    1. HelloWorldPlugin::HelloWorldPlugin(QObject *parent)
    2. : QObject (parent)
    3. {
    4. }
    5.  
    6. QString HelloWorldPlugin::messageString() const
    7. {
    8. return QString("Hello World");
    9. }
    10.  
    11. Q_EXPORT_PLUGIN2 (HelloWorldPlugin, HelloWorldPlugin)
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    the output is

    Qt Code:
    1. HelloWorldPlugin plugin says: "Hello World"
    2. Create New Instance Failed
    3. Found 1 entries
    To copy to clipboard, switch view to plain text mode 
    A camel can go 14 days without drink,
    I can't!!!

  2. #2
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    Default Re: Multiple instance of Plugin object

    It says in Qt's documentation at QMetaObject::newInstance() this:
    Note that only constructors that are declared with the Q_INVOKABLE modifier are made available through the meta-object system.
    I don't see this Q_INVOKABLE macro used in your source code. Try adding it and see what happens.

  3. The following user says thank you to joyer83 for this useful post:

    mcosta (15th June 2011)

  4. #3
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    Default Re: Multiple instance of Plugin object

    Usually you make the plugin a factory that can return instances of interfaces you need:

    Qt Code:
    1. class MyPluginIface : ... {
    2. // ...
    3. public:
    4. virtual MyRealIface * create() = 0;
    5. }
    To copy to clipboard, switch view to plain text mode 

    Then you can create as many instances of MyRealIface as you want.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  5. The following user says thank you to wysota for this useful post:

    mcosta (15th June 2011)

  6. #4
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    Default Re: Multiple instance of Plugin object

    Thank you for the answer.

    Your solution is more elegant than than mine.
    I was courious about QMetaObject::newInstance().

    I solved using joyer83 tips but for a real solution I'll use the factory.
    Last edited by wysota; 15th June 2011 at 17:39.
    A camel can go 14 days without drink,
    I can't!!!

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