GUI in shared library can't find find or load the Qt platform plugin "cocoa"

[Noturnoz]

I have a shared library (.dylib) which contains a function with

int argc = 0;
QApplication app(argc, NULL);
QWidget widget;
widget.resize(100, 100);
widget.show();
app.exec();

I load the shared library in .NET and call the function:

static class AuthDialog{
    [DllImport("libSampleDialog")]
    public static extern void ShowAuthDialog();
}

But when I run the application I get this error:
This application failed to start because it could not find or load the Qt platform plugin "cocoa".

Can someone tell me how can I get this working?

Note: The .dylib is loaded correctly, because anything I print before the QApplication gets printed correctly.