Communicate between two widgets not directly related

Question

I have a GUI with widgets that has multiple child widgets inside, as you can see in the image:

I want to communicate "Widget 2-2" with "Widget 1-1". I have different options, but I don't know which is better.

1. Propagate signal

My first idea was propagates the emit to Main Windows and then it propagates the action to the target widget:

Widget 2-2 emits a signal
Widget 2 catch the emit and emit anther signal
Main Windows catch the emit and call a Widget 1 controller function
Widget 1 controller function calls a Widget 1-1 controller function
Widget 1-1 makes the action

Pros

All the widgets only talks with its parents and children

Cons

It can be a bit messy

2. Create a singleton class with all the signals

Another idea is to create the signals in a singleton class. Then the Widget 2-2 can emit this signals easily and Widget 1-1 can listen this signals easily too. The relative position of the widgets in the architecture does not care, everybody can emit and connect the signals.

Pros

Emit and connect this signals is super easy. Everybody can do it.

Cons

I feel that it is a super bad idea. Probably it will explode in the future, but I don't know why. I prefer to follow the best practices than solve my problem fast and easily (for the moment...)

Singletons are bad patterns. What you seem to be wanting is a simple network client or message bus — OneCricketeer, Jul 16 '22 at 17:08
I would just raise a signal in one widget, and forward it in the first common parent to the other widget. — László Papp, Jul 16 '22 at 17:08
Yes, this is how I have personally done in my small project, at least. But this is likely an opinionated Q/A. Let me know if you want me to submit an answer. — László Papp, Jul 16 '22 at 17:11
For me is ok, but I also will wait to see if anybody has another point of view — Javier Portillo Medina, Jul 16 '22 at 17:14

score 1 · Accepted Answer · answered Jul 16 '22 at 17:15

Singletons, or static initialisation for that matter ought to be the last resort as they can cause all sorts of headaches, especially in multi-threaded environment. Definitely do not go for that in this case.

What I have personally done in my project in this case, I emitted a signal in the first widget and then forwarded that in the first common parent to the second widget so that the second widget handled it via its slot in there.

This has worked fairly well for me, at least. You can forward signals just fine in Qt, i.e. connect a signal to a signal.

The first common parent will encompass both, so you can use it as a proxy for managing the two, or potentially even more widgets in your architecture.

Communicate between two widgets not directly related

1. Propagate signal

Pros

Cons

2. Create a singleton class with all the signals

Pros

Cons

1 Answers1