#17 What the Client Can Do
The app implements one interface with one method. The single parameter of that
method is the other interface — z2ui5_if_client — and it is the whole of what
an app can ask the framework for. Worth knowing by shape before knowing it by
name, because the shape is refreshingly small:
| The app wants to… | …and calls |
|---|---|
| show a screen | view_display( ), popup_display( ), popover_display( ), nest_view_display( ) |
| put ABAP data on that screen | _bind( ) — the attribute, by reference, both directions |
| find out what the user did | check_on_event( ), get_event( ), get_event_arg( ) |
find out why main( ) was called |
check_on_init( ), check_on_navigated( ) |
| talk to the user | message_toast_display( ), message_box_display( ) |
| move to another app and back | nav_app_call( ), nav_app_leave( ), get_app_prev( ) |
| ask the browser to do something | follow_up_action( ) with a cs_event constant |
| know where it runs | get( ) — device, launchpad, URL parameters, the raw event |
That is a framework you can hold in your head. A design goal, not an accident.
The two rows that carry the most weight are the smallest. _bind( ) takes an
ABAP variable and returns the binding path the view needs; the framework builds
the model around whatever was bound, ships it, and writes the user's changes
back into the same variable:
)->tag( `Input`
)->a( n = `value` v = client->_bind( customer )And _event( ) names what the frontend should send when a control fires:
)->tag( `Button`
)->a( n = `text` v = `Save`
)->a( n = `press` v = client->_event( `SAVE` ) ).Both are string generators, and that is all they are. Nothing is registered, nothing is declared: the attribute name and the event name are written into the view, and read back out of the request.
The last row is the escape hatch for everything that is a browser matter rather
than an ABAP matter — focus a field, scroll, copy to the clipboard, download a
file, set the tab title, raise the model size limit. Each is a constant in
cs_event, and each is one call:
client->follow_up_action( val = client->cs_event-set_focus
t_arg = VALUE #( ( `inputCustomer` ) ) ).That is the whole API surface an app ever touches. The full list with every parameter is on the Client API page, generated from the interface itself, so it cannot drift from what the framework actually offers.
One method in, one interface out. Everything an app can do is a method on
client.