Life as Clay

Cocoa Programming for Mac OS X, 4th Edition: Chapter 3 Challenge

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Howdy. I previously wrote some entries about the solutions to the challenges in the Cocoa Programming book, 3rd Edition, by Aaron Hillegass. The 4th edition is good. Like the first edition, however, I find the description of the challenges to be a little vague.

I think he does that on purpose. The solutions usually are simpler than they appear.

The Chapter 3 challenge is, “NSDateFormatter’s setDateFormat: to customize the format string on the date objects in your LotteryEntry class.”.

Here’s what you do.

  • Look for NSDateFormatter in the Xcode documentation. Once you find it, search for the setDateFormat: method. You’ll find that you have to send a string to the method. Perhaps most useful is a link at the top of the class to the “Data Formatting Guide.” Once there, click to the “Date Formatters” page. Aha… here’s where the good info it.
  • Search again for the method name — but only search on this page — for setDateFormat:. You’ll find examples of the type of string that you can use for the date formatter. Copy one of those strings. It will look something like: @"yyyy-MM-dd 'at' HH:mm" or @"yyyy'-'MM'-'dd'T'HH':'mm':'ss"
  • Open LotteryEntry.m in your editor window and find the - (NSString *)description method implementation.
  • What you’re going to do is to replace the formatting that you entered during the chapter with your new format. Your previous method looked like:
- (NSString *)description
{
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setTimeStyle:NSDateFormatterNoStyle];
[df setDateStyle:NSDateFormatterMediumStyle];

NSString *result;
result = [[NSString alloc] initWithFormat:@"%@ = %d and %d",
[df stringFromDate:entryDate],
firstNumber, secondNumber];
return result;
}
  • You want to replace the messages that your sending to your date formatter. Your new method should look like this (with the date string you found):
- (NSString *)description
{
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:@"yyyy-MM-dd 'at' HH:mm"];

NSString *result;
result = [[NSString alloc] initWithFormat:@"%@ = %d and %d",
[df stringFromDate:entryDate],
firstNumber, secondNumber];
return result;
}

That’s it! Run your program and look at the log to see the new format. You can browse through the documentation a bit more to learn more about creating custom formats.

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Written by Clay

January 25, 2012 at 16:14

Posted in Cocoa, Objective-C, Tutorial

Tagged with , ,

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