Using QLibrary to load a QWidget

[luca]

Hi all,
I created a library (under Linux) with Qt Creator containing a QWidget sublass: MyClass.

Now I'm trying to load it with QLibrary from another Qt application.

I don't understand how to proceed after this:
@
QLibrary library("../libs/libmyclass");
@

The documentation show an example:
@
QLibrary myLib("mylib");
typedef void (*MyPrototype)();
MyPrototype myFunction = (MyPrototype) myLib.resolve("mysymbol");
if (myFunction)
myFunction();
@
but this isn't my situation because I need to get a class (QWidget subclass) from the library not a function.

[HuXiKa]

Just include your MyClass.h file, and after that:

@QLibrary library("../libs/libmyclass");
library.load();
if(library.isLoaded()){
MyClass * c = new MyClass;
if(c){
// dostuff
}
}@

[luca]

[quote author="HuXiKa" date="1306873460"]Just include your MyClass.h file, and after that:

@QLibrary library("../libs/libmyclass");
library.load();
if(library.isLoaded()){
MyClass * c = new MyClass;
if(c){
// dostuff
}
}@[/quote]

I thought that using QLibrary there was a way to avoid the need to include .h file .
Isn't that?

[HuXiKa]

You can't use libs without a header file (at least it's not easy). Not just in Qt, but in general.
If you really need something and don't have the header file, use "Dependency Walker":http://www.dependencywalker.com/ and create your own header with help from the program.
But since you wrote the lib yourself, why is it a problem to include that .h file?

[luca]

Thanks,
I'll try to use plugins...

[giesbert]

If you use late binding with dlls (which you do using QLibary::load), you have to use C exported functions, not classes. If you want to use classes (not their interface!) from a dll, you have to link against the dll.

Only option around: using interfaces, which means, create a C exported function as creator function which returns a pointer to an interface (pure virtual class). The disadvantage of this is, you can't create those objects on the heap.

[luca]

[quote author="Gerolf" date="1306910864"]If you use late binding with dlls (which you do using QLibary::load), you have to use C exported functions, not classes. If you want to use classes (not their interface!) from a dll, you have to link against the dll.

Only option around: using interfaces, which means, create a C exported function as creator function which returns a pointer to an interface (pure virtual class). The disadvantage of this is, you can't create those objects on the heap.[/quote]

Thanks,
this is why documentation only show this:
@
QLibrary myLib("mylib");
typedef void (*MyPrototype)();
MyPrototype myFunction = (MyPrototype) myLib.resolve("mysymbol");
if (myFunction)
myFunction();
@

The solution to create a "creator function" also require the header include... right?
So it probably should be better to use a plugin.

[giesbert]

And what do you need to use the plug-in? :-)
the creator function approach uses the interface technique, which means, you have a header for the interface, but not for the specific implementation.

If you use plug-ins (Qt-plugins) and it is enough for you to have the QWidget interface for the class (and the rest only via signal/slot or Q_INVOKEABLE methods) you can use plug-ins. otherwise you also need header files.