Vladimir Prus wrote:
So, if I want to create a widget for drawing graph, I'll have to write:
void draw_the_graph(window w, ....) { ..... }
void handle_click(window w, ....) { // Add new vertex }
void handle_right_click(window w, ...) { // show vertex properties, if mouse points // to a vertex }
window make_graph_widget() { windows w; w.on_draw = &draw_the_graph; w.on_mouse_click = &handle_click; w.on_mouse_right_click = &handle_right_click; return w; }
? What are the chances that handle_right_click can be reused anywhere else,
Slim, but possible.
is it really independent from GUI,
No, but irrelevant.
and isn't this too complex a solution?
No. The alternative solution is comparable in complexity, and as soon as you add another graph widget that has different left or right click behaviors, or make w change its appearance dynamically on response to a combo box cb (by just assigning different drawing functions to w.on_draw in cb.on_change), you'll see why the event-based model is superior. It's not a new invention, just look at Delphi.