On 1/12/2017 6:23 AM, Ernesto wrote:
Hello to everyone,
My name is Ernesto. I am a beginner in Qt programming and I have an
specifics problems whit my first big project (desktop app). Let me explain
myself:
I have to include plugins or add-ons to my application for new file format
types; I looked around QPluginLoader class, Dynamic and Static libraries
classes to achieve this goal, and here is my problem, in each one of this I
have to include the header file and the library (or plugins) in my project.
I have to develop other mini app to create those plugins or libraries. So
here is _my first problem_, I don´t know how many plugins or libraries will
be development to include in my app.
Hello, Ernesto.
I will not address your entire problem (because I'm not clearly understanding
the second one), but your first is easy enough to answer. The answer is: You
don't /need/do know how many plug-ins will be in development.
Plug-ins, by definition, are external code to your main application. You
application needs to /discover/those pieces of external code when it runs.
This way, any number of plug-ins can be included with your application--or
even added later by the user to an existing installation of your
application--without having to modify any of your main application's code.
For example, when your main application starts, it looks in a location--either
hard-coded, or defined by the user--and discovers all the available shared
libraries:
...
QDir plugins("ernestos_plugins");
QStringList plugins_list = plugins.entryList(QStringList() << "*.dll" <<
"*.so", QDir::Files);
...
With each shared library it finds, it tests each to see if it is a plug-in
designed for your application by coercing it to the interface contract,
something like:
foreach(const QString& filename, plugins_list)
{
QString plugin_path =
QDir::toNativeSeparators(QString("%1/%2").arg(plugins.absolutePath()).arg(filename));
QPluginLoader(plugin_path);
QObject* instance = plugin.instance();
if(instance)
{
IErnestoPlugin* iernestofactory =
reinterpret_cast<IErnestoPlugin*>(instance);
if(iernestofactory)
{
...
Each one that supports the contract of your interface ("IErnestoPlugin") can
be safely used within your application as a plug-in designed for your main
application.
I hope I understood the first problem correctly. Apologies if I didn't.
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