Distributing custom Qt plugins in OSX application bundle

I am building a custom application that has certain pieces of the functionality separated out into Qt plugins. This has been working quite well using QPluginLoader and qobject_cast, but up until now, I have been using a hard-coded absolute path (didn't want to complicate things before I had it working!).

I'm getting close to needing to deploy the application to other machines, so I decided to try to package the plugins up into the application bundle (I'm building this primarily for OSX). It took some research, but this is what I've come up with:

MyApp.pro file:

# ...

macx {
    plugins.path = Contents/Plugins
    plugins.files = ../PluginDir-build-desktop/libMyPlugin.dylib

    QMAKE_BUNDLE_DATA += plugins
}

This gives a nice bundle structure that looks something like this:

MyApp.app
 |
 +- Contents
     |
     +- MacOS
     |   |
     |   +- MyApp
     |
     +- Plugins
     |   |
     |   +- libMyPlugin.dylib
     |
     ... other support files ...

So I add the plugin path to the library search paths:

main.cpp:

// ...

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QDir pluginsDir(a.applicationDirPath());
    pluginsDir.cdUp();
    pluginsDir.cd("Plugins");

    a.addLibraryPath(pluginsDir.absolutePath());

    // ...

    return a.exec();
}

And then try to load the plugin, like so:

// ...

QPluginLoader pluginLoader;
pluginLoader.setFileName("libPhotoshopPlugin.dylib");
IMyPluginInterface* plugin = qobject_cast<IMyPluginInterface*>(pluginLoader.instance());

// ...

Unfortunately, plugin always comes out NULL. But when I do this:

// ...

QPluginLoader pluginLoader;
pluginLoader.setFileName("../Plugins/libPhotoshopPlugin.dylib");
IMyPluginInterface* plugin = qobject_cast<IMyPluginInterface*>(pluginLoader.instance());

// ...

I get the plugin instance just fine and everything works as it should.

Why do I have to specify the path in the filename I pass to the QPluginLoader? Shouldn't it pick that up from the QApplication library paths? Is there something I'm just doing stupidly wrong? (I'm guessing and hoping this is more likely)

---

Additional note:

If I change the plugins.path in the MyApp.pro file to Contents/MacOS, the libMyPlugin.dylib get output next to MyApp and everything works just fine. If this is the way I should be doing it anyway, I will gladly continue doing it.

But the Qt documentation shows the Qt plugins (qtjpeg and similar) being开发者_StackOverflow社区 deployed in the Contents/plugins directory and a similar method for adding the directory to the QApplication library path.

---

I store plugins in application.app/Contents/plugins and use the following code to obtain the plugins directory:

...    
#elif defined(Q_OS_MAC)
    QDir pluginsDir = QDir(qApp->applicationDirPath());
    pluginsDir.cdUp();
    pluginsDir.cd("plugins");
#else
...

Now you have the correct path to the plugins dir, and can load the plugin. I also have a file qt.conf in application.app/Contents/Resources with the following contents:

[Paths]
Plugins = plugins