测试NSDatePicker是否等于当前时间

Question

我正在尝试创建一个代码来测试UIDatePicker中选择的日期是否等于当前日期。我想把它作为一个闹钟（用户选择一个时间，他们按一个按钮，并在达到该时间时显示警报）。谢谢！这是我的代码：

#import "AlarmViewController.h"

@interface AlarmViewController ()

@end

@implementation AlarmViewController

NSDate *selectedDate;
NSDate *now;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

 - (void)viewDidLoad
{
    [super viewDidLoad];
    now = [NSDate date];
[_setDatePicker setDate:now animated:YES];
}

    - (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)setAlarm:(id)sender {
selectedDate = [_setDatePicker date];
[self checkDate];

}
-(void)checkDate{
if(selectedDate == now){
        NSString *message = [[NSString alloc]initWithFormat:@"The date and time you selected   
is:    %@", selectedDate];
    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"time selected" message:message   
delegate:Nil cancelButtonTitle:@"ok" otherButtonTitles:nil];
    [alert show];
}
}
@end