NSTimer(Chapter 24 of Cocoa Programming for Mac OS X)

 1 #import "AppController.h"
 2 #import "BigLetterView.h"
 3 
 4 #define MAX_COUNT (100)
 5 #define COUNT_STEP (5)
 6 
 7 @implementation AppController
 8 
 9 - (id)init
10 {
11     [super init];
12     
13     letters = [[NSArray alloc] initWithObjects:@"a", @"s", @"d", @"f", @"j", @"k", @"l", @";", nil];
14     srandom(time(NULL));
15     return self;
16 }
17 
18 - (void)awakeFromNib
19 {
20     [self showAnotherLetter];
21 }
22     
23 - (void)resetCount
24 {
25     [self willChangeValueForKey:@"count"];
26     count = 0;
27     [self didChangeValueForKey:@"count"];
28 }
29 
30 - (void)incrementCount
31 {
32     [self willChangeValueForKey:@"count"];
33     count = count + COUNT_STEP;
34     if (count > MAX_COUNT) 
35     {
36         count = MAX_COUNT;
37     }
38     [self didChangeValueForKey:@"count"];
39 }
40 
41 - (void)showAnotherLetter
42 {
43     int x = lastIndex;
44     while (x == lastIndex) 
45     {
46         x = random() % [letters count];
47     }
48     lastIndex = x;
49     [outLetterView setString:[letters objectAtIndex:x]];
50     
51     [self resetCount];
52 }
53 
54 - (IBAction)stopGo:(id)sender
55 {
56     if (timer == nil) 
57     {
58         NSLog(@"Starting");
59         
60         timer = [[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(checkThem) userInfo:nil repeats:YES] retain];
61     }
62     else 
63     {
64         NSLog(@"Stopping");
65         [timer invalidate];
66         [timer release];
67         timer = nil;
68     }
69 }
70 
71 - (void)checkThem:(NSTimer *)aTimer
72 {
73     if([[inLetterView string] isEqual:[outLetterView string]])
74     {
75         [self showAnotherLetter];
76     }
77     if (count == MAX_COUNT) 
78     {
79         NSBeep();
80         [self resetCount];
81     }
82     else 
83     {
84         [self incrementCount];
85     }
86 
87 }
88 
89 @end