Rails apps use a method in date_helper.rb called distance_from_time_in_words that tells approximately how long ago something happened, e.g., "10 seconds ago" or "Almost 3 hours ago." This app duplicates this functionality in Objective-C (appropriately, it does so approximately). The magic of it all is found in a category, NSDate+Formatting, that you can use in your own applications. In fact, the app exists only to demonstrate how to use the category.
Copyright 2011 Rob Warner @hoop33 rwarner@grailbox.com http://grailbox.com
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
Open the project in Xcode and run it. You can also run its unit tests (Cmd+U) which run a series of tests against the four methods in the NSDate+Formatting category (see below for more info on the methods). To use the app, spin the date picker backward and forward to see the "distance of time in words" between now and the selected time. You can change the mode of the date picker control to Time, Date, and Date & Time by clicking on the appropriate segment. You can reset the date to now by clicking the "Reset date to now" button.
To use NSDate+Formatting in your application, copy NSDate+Formatting.h and NSDate+Formatting.m into your project. These four methods then become available for all of your NSDate instances:
- (NSString *)formatWithString:(NSString *)format;- (NSString *)formatWithStyle:(NSDateFormatterStyle)style;- (NSString *)distanceOfTimeInWords;- (NSString *)distanceOfTimeInWords:(NSDate *)date;
The first two (the ones that start with format) make date formatting cleaner in your code. Instead of explicitly creating, using, and release date formatters in your code, you can just call these methods directly on your date objects, passing the format string or style that you would have passed to your formatter. Examples:
[[NSDate date] formatWithString:@"MM-dd-yyyy"];[[NSDate date] formatWithStyle:NSDateFormatterFullStyle];
The next two relate to each other. Calling distanceOfTimeInWords with no parameters returns the distance between the source date and now. Passing a date to distanceOfTimeInWords returns the distance between the source date and the passed date. Examples:
[[NSDate date] distanceOfTimeInWords];[[NSDate date] distanceOfTimeInWords:[[NSDate date] dateByAddingTimeInterval:86400]];
NSDate+Formatting uses localized strings, so if you localize your app and provide strings for all that NSDate+Formatting uses, your returned string will be localized. The app provides both english and Spanish localizations.