UIDatePicker默认返回Null吗？

Question

My implementation for UIDatePicker is essentially this one .

My problem is that if the UIDatePicker pops up and the user doesn't change the date and just hits done, I get exc_bad_access because if done is hit without having moved the time by a minute or more, it seems to be returning null.

I pull the NSDate for the UIDatePicker and pass it to a method that does a calculation on it, however when done is just hit, it crashes.

Is there any way to set the default value of the UIDatePicker, or just have it be the value that pops up? (Which is typically the current time, but still returns null). I've been searching for a way to either set the default value to midnight, or to have it simply set the current time that it pops up as.

Here's my attempt at setting it to midnight (didn't work, crashed):

NSString *myDateAsAStringValue=@"2011-08-27 00:00:00 +0000";
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:@"yyyy-MM-dd hh:mm:ss a"];
NSDate *myDate = [df dateFromString: myDateAsAStringValue];
[datePicker setDate:myDate];
[self changeDate:datePicker];

Here's the code from fluchpunkt if you don't wanna bother going through the link:

- (void)changeDate:(UIDatePicker *)sender {
 NSLog(@"New Date: %@", sender.date);
}

- (void)removeViews:(id)object {
 [[self.view viewWithTag:9] removeFromSuperview];
 [[self.view viewWithTag:10] removeFromSuperview];
 [[self.view viewWithTag:11] removeFromSuperview];
}

- (void)dismissDatePicker:(id)sender {
 CGRect toolbarTargetFrame = CGRectMake(0, self.view.bounds.size.height, 320, 44);
 CGRect datePickerTargetFrame = CGRectMake(0, self.view.bounds.size.height+44, 320, 216);
 [UIView beginAnimations:@"MoveOut" context:nil];
 [self.view viewWithTag:9].alpha = 0;
 [self.view viewWithTag:10].frame = datePickerTargetFrame;
 [self.view viewWithTag:11].frame = toolbarTargetFrame;
 [UIView setAnimationDelegate:self];
 [UIView setAnimationDidStopSelector:@selector(removeViews:)];
 [UIView commitAnimations];
}

- (IBAction)callDP:(id)sender {
 if ([self.view viewWithTag:9]) {
  return;
 }
 CGRect toolbarTargetFrame = CGRectMake(0, self.view.bounds.size.height-216-44, 320, 44);
 CGRect datePickerTargetFrame = CGRectMake(0, self.view.bounds.size.height-216, 320, 216);

 UIView *darkView = [[[UIView alloc] initWithFrame:self.view.bounds] autorelease];
 darkView.alpha = 0;
 darkView.backgroundColor = [UIColor blackColor];
 darkView.tag = 9;
 UITapGestureRecognizer *tapGesture = [[[UITapGestureRecognizer alloc]     initWithTarget:self         action:@selector(dismissDatePicker:)] autorelease];
 [darkView addGestureRecognizer:tapGesture];
 [self.view addSubview:darkView];

 UIDatePicker *datePicker = [[[UIDatePicker alloc] initWithFrame:CGRectMake(0, self.view.bounds.size.height+44, 320, 216)] autorelease];
 datePicker.tag = 10;
 [datePicker addTarget:self action:@selector(changeDate:)     forControlEvents:UIControlEventValueChanged];
 [self.view addSubview:datePicker];

 UIToolbar *toolBar = [[[UIToolbar alloc] initWithFrame:CGRectMake(0, self.view.bounds.size.height, 320, 44)] autorelease];
 toolBar.tag = 11;
 toolBar.barStyle = UIBarStyleBlackTranslucent;
 UIBarButtonItem *spacer = [[[UIBarButtonItem alloc]     initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil] autorelease];
 UIBarButtonItem *doneButton = [[[UIBarButtonItem alloc]     initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(dismissDatePicker:)] autorelease];
 [toolBar setItems:[NSArray arrayWithObjects:spacer, doneButton, nil]];
 [self.view addSubview:toolBar];

 [UIView beginAnimations:@"MoveIn" context:nil];
 toolBar.frame = toolbarTargetFrame;
 datePicker.frame = datePickerTargetFrame;
 darkView.alpha = 0.5;
[UIView commitAnimations];
}

Answer 1

Just go and download this code from github. It is what u need with a demo project inside.

here