I am developing under Windows and I have a Qt plugin project that produces a dll, and I have another app that can load that dll dynamically as a plugin via the usual Qt methods. Basically what I wanted to do was have the plugin report its status back to this app that's using it (i.e. the plugin emits a signal, the app receives it via a slot). So after I successfully detect and read in the plugin (i.e. the dll file), I do the usual connect call to set up the signal/slot (which returns true), but the connection doesn't seem to actually be working, as my slot code never gets executed in the app. I tried to strip down the pertinent code below.


UpgradeInterface.h (this is the interface a plugin extends):

Qt Code: 
  1. class UpgradeInterface : public QObject
  2. {
  3. public:
  4.  
  5.     virtual ~UpgradeInterface() {}
  6.     virtual bool performUpgrade() = 0;
  7.  
  8. signals:
  9.       void statusUpdate(QString statusMsg);
  10. };
  11.  
  12. Q_DECLARE_INTERFACE(UpgradeInterface, "com.UpgradeInterface/1.0")
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//----------------------------------------------------------

UpgradePlugin.h:

Qt Code: 
  1. class UpgradePlugin : public QObject, public UpgradeInterface
  2. {
  3.     Q_OBJECT
  4.     Q_INTERFACES(UpgradeInterface)
  5.  
  6. public:
  7.     bool performUpgrade();
  8.  
  9. signals:
  10.       void statusUpdate(QString statusMsg);
  11. };
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//----------------------------------------------------

UpgradePlugin.cpp:

Qt Code: 
  1. bool UpgradePlugin::performUpgrade()
  2. {
  3.     emit statusUpdate("Upgrade started!");
  4.     return true;
  5. }
  6.  
  7. Q_EXPORT_PLUGIN2(UpgradePlugin, UpgradePlugin)
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//-------------------------------------------------

The following is part of the app code that detects/loads the plugin.

MyDialog.h:

Qt Code: 
  1. class MyDialog : public QDialog
  2. {
  3.       Q_OBJECT
  4. //...
  5. //...
  6. protected slots:
  7.       void statusUpdateFromUpgradePlugin(QString statusMsg);
  8. };
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//------------------------------------------------------

MyDialog.cpp:

Qt Code: 
  1. void MyDialog::loadPlugins(QDir dir)
  2. {
  3.     // Load dynamic plugins
  4.  
  5.     foreach (QString fileName, dir.entryList(QDir::Files)) 
  6.       {
  7.         QPluginLoader loader(dir.absoluteFilePath(fileName));
  8.         QObject *plugin = loader.instance();
  9.  
  10.         if (plugin) 
  11.             {
  12.                   UpgradeInterface * iUpgrade = qobject_cast<UpgradeInterface *>(plugin);
  13.                   if (iUpgrade)
  14.                   {
  15.                         bool success = connect(iUpgrade, SIGNAL(statusUpdate(QString)), this, SLOT(statusUpdateFromUpgradePlugin(QString))); // returns true
  16.                         iUpgrade->performUpgrade();               
  17.                   }
  18.             }
  19.       }
  20. }
  21.  
  22. void MyDialog::statusUpdateFromUpgradePlugin(QString statusMsg)
  23. {
  24.       cout << statusMsg;  // Never gets here!
  25. }
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