Softwareentwicklung in C++ - ASC

292 10. Memory – ein kleines Beispiel
66
67 /∗ Writes the number to the context . This method can only work
68 ∗ with a text context .
69 ∗ @param context The output context to write to .
70 ∗/
71 virtual void writeDisplayRep ( OutputContext &context )
72 {
73 dynamic cast(context ) . write ( t e x t ) ;
74 }
75
76 } ;
77
78 #endif // s i m p l e t e x t d i s p l a y a b l e h
10.2.18 Event
Da die Entscheidung beim Reagieren auf den User-Input zugunsten eines
sauberen Event Modells gefallen ist, brauchen wir einmal eine Basisklasse
Event. Diese benötigt eigentlich keine besondere, tiefergehende Erklärung:
1 // simple event . h − simple c l a s s f o r events
2
3 #ifndef s i m p l e e v e n t h
4 #define s i m p l e e v e n t h
5
6 #include ” u s e r t y p e s . h”
7
8 //−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
9 /∗ A very simple base c l a s s f o r events . All events have to be
10 ∗ derived from i t and f o r each event type a corresponding
11 ∗ constant has to be placed here . This base does nothing but
12 ∗ s t o r e the type of the event so that i t can be asked f o r i t .
13 ∗ All f u n c t i o n a l i t y f o r s p e c i a l events has to be implemented
14 ∗ in the appropriate derived c l a s s e s .
15 ∗/
16
17 class Event
18 {
19 protected :
20
21 /∗ The type of the event . Must be one o f the constants below
22 ∗/
23 int32 event type ;
24
25 public :
26
27 /∗ Constants f o r p o s s i b l e event types . I f a new type i s
28 ∗ introduced an according constant has to be placed here .
29 ∗/
30 static const int32 WORDEVENT = 0x1 ;
31
32 /∗ Standard constructor
33 ∗ Has to s t o r e the type i n t e r n a l l y . No checks f o r v a l i d types
34 ∗ are performed because events are u s u a l l y generated extremely
35 ∗ often and t h e r e f o r e performance i s an i s s u e .
36 ∗ @param event type The type of the event . Has to be one o f
37 ∗ the constants above
38 ∗/
39 explicit Event ( int event type )
40 {
41 event type = event type ;