Although the same session component could also implement the Graphical Presenter
roll, there is a FIDL protocol,
that allows a session component to delegate Graphical Presenter
responsibilities another component. This makes it possible for each component to
execute in different runtimes (such Rust versus Flutter/Dart) if needed.
Displaying element views
For Fuchsia-based products running on devices with a graphical display, a session implementation manages displayable components through the Element API. Each element renders its graphical representation in what is known as a "view".
A session will request the Element's view, and then pass that view to the Graphical Presenter to be displayed, along with optional Element Annotations, used to communicate product-specific presentation properties.
The session calls the
PresentView() to display a
ViewSpec, through which the session conveys where and how it wants the
view to be displayed in the
AnnotationController, which is a handle to the element's annotations, through
which the presenter can update the respective element's annotations.
In return, the caller is given a handle to
the view, as a
ViewController. The caller can destroy
the view (remove it from the display) by releasing or closing its
The developer guide includes an example implementation of presenting an element's view.