[Qt-interest] Plugin framework

[Tim Peeters]

My apologies, I only discovered the QPluginLoader::errorString() function
now.
So if I include this line:
    if (!loader.load()) cout<<"error:
"<<qPrintable(loader.errorString())<<endl;
instead of the cout<<"bla" below, it prints the following error message:


error: Cannot load library
/home/tim/dtibuild/new/bin/libbmia_BogusPlugin.so:
(/home/tim/dtibuild/new/bin/libbmia_BogusPlugin.so: undefined symbol:
_ZTV11BogusPlugin)

Unfortunately I still do not know how to solve this :(

Tim.


On Mon, Nov 23, 2009 at 23:38, Tim Peeters <thjmpeeters at gmail.com> wrote:

> Hi,
>
> I'm trying to write software that can be extended using plugins.
> I follow the guidelines as given on
> http://qt.nokia.com/doc/4.5/plugins-howto.html#the-lower-level-api-extending-qt-applications
>
> I created a simple interface:
>
> class TestInterface
> {
>   public:
>     virtual ~TestInterface() {}
>     virtual int testFunction() = 0;
> };
> Q_DECLARE_INTERFACE(TestInterface, "bmia.plugin.TestInterface/1.0")
>
>
> and a plugin class:
>
> class BogusPlugin : public QObject, public TestInterface
> {
>     Q_OBJECT
>     Q_INTERFACES(TestInterface)
>
> public:
>     int testFunction();
> }
>
> and implementation:
>
> int BogusPlugin::testFunction()
> {
>   return 2;
> }
> Q_EXPORT_PLUGIN2(BogusPlugin, BogusPlugin)
>
>
> And I created a Manager class to manage my plugins. For now I have this
> function to load a simple plugin:
>
> bool Manager::load(string filename)
> {
>     cout<<"Going to try to load plugin from file "<<filename<<endl;
>
>     QPluginLoader loader(QString(filename.c_str()));
>
>     QFile* file = new QFile();
>     file->setFileName(loader.fileName());
>     cout<<"file exists = "<<file->exists()<<endl;
>     delete file;
>
>     if (!loader.load()) cout<<"bla"<<endl;
>
>     QObject* loadedQObject = loader.instance();
>     if (!loadedQObject)
>     {
>     cout<<"Plugin from file "<<filename<<" could not be loaded."<<endl; //
> XXX: replace by core warning message, also below.
>     return false;
>     } // if
> return true;
> }
>
> And I have a test program to see if I can load the BogusPlugin:
>
> int main(int argv, char *args[])
> {
>    QApplication app(argv, args);
>    plugin::Manager* m = new plugin::Manager();
>    m->load("libbmia_BogusPlugin.so");
>    return app.exec();
> }
>
> When I run the program, I get the following:
>
> $ ./fakeplugin
> Going to try to load plugin from file libbmia_BogusPlugin.so
> file exists = 1
> bla
> Plugin from file libbmia_BogusPlugin.so could not be loaded.
>
>
> All I know from this is that QPluginLoader.load(..) function returns false
> and the plugin is not properly loaded.
> But I cannot discover why this is happening. For building we use CMake. The
> supposed plugin is compiled as a dll (bmia_BogusPlugin.so on linux), and the
> main function is compiled for the fakeplugin executable that should load the
> plugin. The file can be found, but no plugin is loaded from this.
>
> Does anyone have an idea on what may be my problem? Maybe I am missing
> something?
>
> Thanks,
> Tim.
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.qt-project.org/pipermail/qt-interest-old/attachments/20091123/37e9d6bf/attachment.html