Imperative workflow in C++/Qml application

Hi,

I'm working on a desktop application written in C++ with UI code in Qml. It's a typical 3d (engineering) application (think something like autocad, 3dsmax,..., but smaller). There is one thing which often comes back and to which I didn't find a satisfying solution yet and that's handling "a workflow with questions to the user". To give an example: Let's say the user wants to start a new project when another one is open - if there are changes, ask whether to save them or not - if no, quit, start a new project and ask properties for this project to open, if yes, check if there is already a file/folder to save - if no, ask a file to save, if yes check the types of items in the project - Depending on the type of items, ask the user if they are needed to be saved in the project or not - if not, go to next type, if yes, check if this item type needs certain "save settings" (for instance compression factor of a picture, whether to save a 3d model binary or ascii,...), and so on and so on... .
Every time, i try to invent a new approach to solve such problems, but I never found a good solution. The reason is there is a lot of (already working) imperative code (and my mindset is probably to imperative :-)). Is there some sort of design pattern to follow to keep this clean? Or how do you solve such problems?
Thanks for the ideas,

Jan

As you've said yourself there are quite a number of ways to do that.

One approach that i find rather elegant myself is the request handler pattern used for example by the QML API of WebEngineView.

The C++ side emits a signal that transports a request context, which is then used by the QML side to communicate the result back.

See for example http://doc.qt.io/qt-5/qml-qtwebengin...quested-signal

If you know or require that the QML side uses a modal dialog and thus a nested event loop, then you can retrieve the user's input right after the emit returns.

Code:

---

RequestContext context;
 
emit requestDialog(&context);
 
// continue in "linear" workflow

---

If you want to handle the nested event loop on the C++ side, it will look more like this:

Code:

---

RequestContext context;
QEventLoop loop;
 
connect(&context, &RequestContext::done, &loop, &QEventLoop::quit);
 
emit requestDialog(&context);
 
// check if dialog has not already been
if (!context.isDone() {
    loop.exec();
}
 
// continue in "linear" workflow

---

Cheers,
_