Question

The function below (i.e. dateChanged()) is triggered by a UIDatePickersolve . My problem is that

NSLog(@"Future: %@", futureDate);

returns ‘null’. However,

NSLog(@"Today: %@", today);

works just fine.

I know that casting sender as a UIDatePicker, allows me to solve the problem using:

futureDate = [dateFormat stringFromDate:sender.date];

but I cannot understand why I cannot cast sender as an NSDate. Any insight would be much appreciated.

//- (IBAction)dateChanged:(UIDatePicker*)sender {
  - (IBAction)dateChanged:(NSDate *)sender {
     NSDate* todaysDate = [NSDate date];
     NSDateFormatter* dateFormat;
     dateFormat=[[NSDateFormatter alloc] init];
     [dateFormat setDateFormat:@"MMMM d, yyyy hh:mm:ssa"];
     NSString * today;
     NSString * futureDate;
     today=[dateFormat stringFromDate:todaysDate];
     NSLog(@"Today: %@", today);
     futureDate = [dateFormat stringFromDate:sender];
     NSLog(@"Future: %@", futureDate);
   }

Answer 1

Sure you can cast sender to be NSDate*. Or UIButton* – or whatever else. However it does’t change the fact that date picker implementation sends an UIDatePicker* as a parameter of delegate message and the casting will be invalid. The most flexible delegate messages have id as a type of returned parameter, but the object passed is always an object of a certain class. And the Objective-c casting only makes your debugging and dev process easier with code completion and warnings for the casted class.