GUI - Events and actors

---

Events:

Mouse clicking, mouse hovering, key pressing etc., are events that you may want to associate with code. We saw on last chapter that there is something called action facet that executes code triggered by a default event. You can add more blocks of code associated with events by following this layout:

There is an extensive list of possible events in the documentation. I copied it at the end of this chapter for reference.

Each face accepts a set of events, i.e. not all events apply to all faces.

I made a short set of examples. I see no point in giving examples of each existing event, since the logic is the same:

down - left mouse button pressed; 

over - mouse cursor passing over a face;

Red [needs: view]

view [

       t: area 40x40 blue

       on-down [quit]

       on-over [either t/color = red [t/color: blue][t/color: red]]

]

wheel - mouse wheel being turned;

Red [needs: view]

list: ["first" "second" "third" "fourth"]

view [

       t: text "Place your cursor over here and roll the wheel"

               on-wheel [

                       t/text: first list

                       list: next list

                       if tail? list [list: head list]

               ]                

]

key-down - a key has been pressed;

Red [needs: view]

list: ["key" "another key" "one more key"]

view [

       below

       text "Click inside field and press a key"

       t: text 100

       a: field

               on-key-down [

                       t/text: first list

                       list: next list

                       if tail? list [list: head list]

               ]

]

time - the delay set by face’s  rate facet expired.

The following example "blinks" a text at a 1 second rate (see rate in chapter GUI- Advanced topics):

Red [needs: view]

view [

       t: text "Now you see..." rate 1

               on-time [either t/text = "" [t/text: "Now you see..."][t/text: ""]]

]

close - this is a window event: the window was closed. Very useful to include code to be executed when the user quits (closes the window).

Red [needs: view]

view [

       on-close [print "bye!"]        

       button [print "click"]

]

 Actors

Actors is the name of the event handling functions in Red. That is, the code inside the block after on-<event> . So why not call them just event handlers like most other language do? I think is because they are an object inside the face as you can see if you run this code below and click on the area face:

Red [Needs: view]

view [

       t: area 40x40 blue on-down [print t] ;click to quit

       on-over [either t/color = red [t/color: blue][t/color: red]]

]

You will see in the console, nearly at the end of the print, an object with the actors described:

(...)

edge: none

para: none

font: none

actors: make object! [

   on-down: func [face [object!] event [event! none!]][print t]

   on-over: func [face [object!] event [event! none!]][either t/color = red [t/color: blue] [t/color: red]]

]

extra: none

draw: none

(...)

on-create actor:

In addition to the GUI events, it is possible to define an on-create actor which will be called when the face is shown for the first time, just before system resources are allocated for it. Unlike other actors, on-create has only one argument, face.

Full list of event names:

Notes:

• touch events are not available for Windows XP.+
• One or more moving events always precedes a move one.
• One or more resizing events always precedes a resize one.

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