Add an MVVM example

[urbytes21]

No description provided.

[Copilot]

Pull request overview

Adds a new MVVM-based GTKmm sample app alongside the existing MVC example to demonstrate architectural differences and trade-offs.

Changes:

• Introduces an MVVM example (mvvm_ap) with a SharedData model, SharedDataVM ViewModel, and two Views (EditorWidget, DisplayWidget).
• Updates build configuration to compile the new MVVM executable.
• Updates documentation to include an MVC vs MVVM trade-offs table; also makes small MVC observer/include adjustments.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/ap/mvvm/IObserver.h	Adds MVVM-local observer interface used by model/viewmodel/views.
src/ap/mvvm/model/SharedData.h	Defines MVVM model holding shared state and notifying observers.
src/ap/mvvm/model/SharedData.cpp	Implements MVVM model state updates + observer notification.
src/ap/mvvm/viewmodel/SharedDataVM.h	Defines ViewModel mediating model updates to views.
src/ap/mvvm/viewmodel/SharedDataVM.cpp	Implements ViewModel commands and forwarding notifications to views.
src/ap/mvvm/view/EditorWidget.h	Declares editor view that submits user input to the ViewModel.
src/ap/mvvm/view/EditorWidget.cpp	Implements editor UI and self-registration with the ViewModel.
src/ap/mvvm/view/DisplayWidget.h	Declares display view that renders ViewModel-provided state.
src/ap/mvvm/view/DisplayWidget.cpp	Implements display UI and updates on ViewModel notifications.
src/ap/mvvm/mvvm_ap.cpp	Wires up the MVVM app window, constructing model/viewmodel/views.
src/ap/mvvm/CMakeLists.txt	Builds and links the new mvvm_ap executable.
src/ap/CMakeLists.txt	Enables building the mvvm subdirectory.
src/ap/mvc/IObserver.h	Adds missing <string> include for std::string usage.
src/ap/mvc/model/SharedData.cpp	Adjusts observer iteration style in MVC model implementation.
src/ap/README.md	Replaces the old examples section with an MVC vs MVVM trade-offs table.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The MVVM container is still registering Views directly with the Model. Since SharedDataVM already subscribes to the Model and Views self-register with the ViewModel, these addObserver() calls will make each View receive duplicate notifications (from both Model and ViewModel) and undermines the MVVM separation described above. Remove these registrations so only the ViewModel observes the Model.

Suggested change

	dataModel_->addObserver(editorView_.get());
	dataModel_->addObserver(displayViewLeft_.get());
	dataModel_->addObserver(displayViewRight_.get());

[Copilot]

This window title still says "MVC Integrated Demo" even though this is the MVVM example (and the app id is singlemvvm). Update the title to avoid confusing users/readers.

Suggested change

	set_title("MVC Integrated Demo");
	set_title("MVVM Integrated Demo");

[Copilot]

The class comment says views receive a shared_ptr, but the actual type used throughout is SharedDataVM. Update the comment to match the real type name to prevent confusion in this example.

Suggested change

	* 3. Views receive a shared_ptr<SharedDataViewModel>, never a Model pointer.
	* 3. Views receive a shared_ptr<SharedDataVM>, never a Model pointer.

[Copilot]

updateLabel() builds Pango markup by concatenating unescaped user-provided text. If the text contains markup characters (e.g. '<', '&'), the label will render incorrectly or fail to parse; it also allows markup injection. Escape the text (e.g., Glib::Markup::escape_text) before embedding it, or use set_text() and apply styling via CSS instead of markup.