iOS 8 & Xcode 6：UIAlertView取消时不回调alertViewCancel:

在做UIAlertView取消操作时，发现委托函数alertViewCancel:并不被调用，只好在alertView: didDismissWithButtonIndex:中进行判断。

 1 @interface DateViewController () <UIAlertViewDelegate>
 2 @property (weak, nonatomic) IBOutlet UIDatePicker *datePicker;
 3
 4 @end
 5
 6 @implementation DateViewController
 7
 8 - (void)viewDidLoad {
 9     [super viewDidLoad];
10     NSDate *now = [NSDate date];
11     [self.datePicker setDate:now animated:NO];
12 }
13
14 - (void)didReceiveMemoryWarning {
15     [super didReceiveMemoryWarning];
16     // Dispose of any resources that can be recreated.
17 }
18
19 - (IBAction)buttonPress:(UIButton *)sender {
20     NSDate *selectedDate = self.datePicker.date;
21     NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
22     fmt.dateFormat = @"yyyy - MM - dd";
23
24     NSString *string = [NSString stringWithFormat:@"You selecte %@", [fmt stringFromDate:selectedDate]];
25     UIAlertView *view = [[UIAlertView alloc] initWithTitle:@"Date Picker"
26                                                    message:string
27                                                   delegate:self
28                                          cancelButtonTitle:@"Cancel"
29                                          otherButtonTitles:@"OK", nil];
30     [view show];
31 }
32
33 - (void)alertViewCancel:(UIAlertView *)alertView {
34     NSLog(@"View canceled.");
35 }
36
37 - (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex {
38     NSLog(@"buttonIndex = %zi", buttonIndex);
39 }
40
41 @end

日志输出如下，取消按钮序号为0，其他按钮序号按添加次序递增。