Whether you subscribe to Test Driven Development (TDD) or another testing practice, when it comes automated unit testing with Core Data, things can be a little tricky. But if you keep it simple, and take things step by step, you can get up and running with unit testing using Core Data fairly quickly. We’ll explore the what, how and why of unit testing with Core Data. We’ll also be using the helper library MagicalRecord. MagicalRecord not only lets us get up and running faster, but helps to cut down on the noise in our tests.
A couple of weeks ago Matt Long was having a problem with an app running out of memory. He had a ginormous data file he needed to load up and process, and that memory hit was more than the app could bear. It would load just fine, into an NSData, but before he could finish with it the app would run short of memory and die.
Until recently the obvious thing would have been to tell NSData to create a memory-mapped instance. Given
NSString *path pointing to a file, you could create an NSData with almost no memory hit regardless of file size by creating it as:
NSData *data = [NSData dataWithContentsOfMappedFile:path];
Starting with iOS 5 though, this method has been deprecated. Instead, what you’re supposed to do is:
NSError *error = nil; NSData *data = [NSData dataWithContentsOfFile:path options:NSDataReadingMappedAlways error:&error];
So, fine, whatever, it’s a different call, so what? Well, it wasn’t working. Instruments was showing that the app was taking the full memory hit when the NSData was created. Mapping wasn’t working despite using NSDataReadingMappedAlways. So what could he do? The wheels of my mind started turning.
With the March 1st start date approaching when sandboxing becomes a requirement for submissions to the Mac App Store, I’ve been considering my options. (more…)
A few months ago I wrote here about a generic approach to safely take incoming JSON and save values to Core Data object. The goals of that code were twofold:
- Provide a safe, generic alternative to Cocoa’s
-setValuesForKeysWithDictionary:for use with NSManagedObject and its subclasses
- Handle cases where JSON data didn’t match up with what the managed objects expected. Getting a string where you expect a numeric value, or vice versa, for example, or getting a string representation of a date when you want a real NSDate object.
The first item was the most important. It’s tempting to use
-setValuesForKeysWithDictionary: to transfer JSON to a model object in one step. The method runs through the dictionary and calls
-setValue:forKey: on the target object for every entry. It has a fatal flaw though, in that it doesn’t check to see if the target object actually has a key before trying to set it. Using this method when you don’t have absolute control over the dictionary contents is an invitation to unknown key exceptions and nasty app crashes.
Fixing this for managed objects was relatively easy because Core Data provides convenient Objective-C introspection methods. The general approach was:
- Get a list of the target object’s attributes
- For each attribute, see if the incoming dictionary has an entry. If so,
- Compare the incoming type to the expected type, and convert if necessary.
-setValue:forKey:with that key and its value.
And then just last week I had the thought, wouldn’t it be nice if this worked for any object, not just for managed objects?
Recently on StackOverflow I have seen several questions regarding the desire for a parent Entity to be updated whenever an attribute within the child has changed.
There are several different ways to solve this problem. The easiest is to have the child ping the parent whenever it changes and then the parent can update any values it needs to as a result of that ping. (more…)
Note: This is a re-print from the Mac Developer Network.
One of the nice things about developing software for OS X is all the “freebies” we get out of Cocoa. For example, when we are building a UI with text input we get undo support for free! How cool is that?
Likewise, when we are working with Core Data, it also has undo support built right in. Every
NSManagedObjectContext has a NSUndoManager that we can use. However there are some situations where the default undo support is insufficient.
In this article we are going to walk through one such situation. (more…)
Note: This is a re-print from the Mac Developer Network.
I tend to frequent the StackOverflow website and watch for questions about Core Data. Generally if it is a question I can answer I will and if it is a question I can’t answer then I really dig in for a fun session of exploration and attempt to find the answer. (more…)
When: November 2-4, 2011
Where: Los Angeles, CA
The speaker line up for MacTech this year is amazing. I am quite honored to be sharing the stage with such a group of people.
What is MacTech Conference?
MacTech Conference is a 3-day, immersive, technical conference specifically designed for Apple developers, IT Pros, and Enterprise. “The whole idea of MacTech Conference is to allow members of the Apple community to meet and exchange ideas,” said Edward Marczak, Conference Chair and Executive Editor of MacTech Magazine. “This will be spurred on by presentations from some of the best and well-known experts in the community.”
MacTech Conference will have two separate tracks: one focused on programming / development, and the other on IT/Enterprise. Sessions will focus on both desktop and mobile, with appropriate levels of attention paid to the Mac, iPhone, iPad and iPod.
Core Data has many features, one of which is the Transient attribute. This type of attribute on a Core Data entity is part of a data model, but is not persisted in your Core Data persistent store. If you open up the raw SQLite store file and peek at the schema, you will not find any transient attributes. These transient attributes are still handy despite no data being persisted to the data store. One useful scenario is when a value is calculated based on other attributes. This calculation can be performed in an entity’s awakeFromFetch method, and stored at run time in this transient attribute.
One scenario I’ve been asked about on more than one occasion recently is that of temporary, or transient entities. It seems that more and more developers have a need for temporary, or transient instances of entities in your Mac or iOS apps. Having temporary object instances can be useful and necessary in certain situations. Unfortunately, Transient Entities do not technically exist within the Core Data framework, however there are simple solutions to add temporary, un-persisted, data within the context of Core Data. Let’s go over some methods to effectively use the concept of Transient, or more appropriately Temporary Entities in Core Data without direct built-in support.
When: September 11-14, 2011
Where: Denver, Colorado
I am very pleased to announce that I will be speaking at this year’s 360 iDev conference in Denver, Colorado. Previously it was a foregone conclusion that I would be attending this conference since it was so close to my home. However, now that I am living in California, that is no longer the case.
However, I am happy to say that I will be attending this year despite a change in my home address. The speaker line up at 360 iDev keeps getting better each year and I am happy to be a part of this great lineup.
If you are on the fence about going to this conference then please take my advice; GO.
Not only is the speaker line up great but Denver has a great walking downtown and the after session events should be just as entertaining as the speakers themselves.
I look forward to seeing you there.
When: September 5-7, 2011
Where: Brighton, UK
I am very pleased to announce that I will be speaking in Brighton at the Update conference starting on September 5, 2011. The Update conference is a bit different than the normal “developer” conference that I attend and speak at. Instead of just or primarily focusing on the developer; a great deal of focus is put upon the user and the user experience. If you have been in attendance for any of Aral Balkan’s talks then you know very well what his focus is.
In addition to speaking at the conference I will be giving two one day workshops on Core Data. The first workshop will be an introduction to Core Data. I hesitate to call this a beginner workshop because you, the attendees, will be directing the workshop. If everyone wants to start at step one then we will. However throughout the day you will be setting the pace of what we learn and discuss. This format has worked very well in the past and the last time we did a workshop like this the day ended with some pretty advanced discussions.
The second session is labelled advanced and will be starting off with the assuming that we all know and understand the principals behind Core Data. In this session we will deep dive into some of the more complex areas of Core Data. Again, I have a list of topics but you, the attendees, drive the session. Therefore it is intentionally open ended so that you can come with your questions and problems and we can discuss them together. I plan on wrapping up the second workshop with some real world examples of edge cases and situations I have run into and how they were solved.
I invite you to join me in Brighton this September to attend Update 2011. I expect it to be a great time.
This is a post that has been sitting in the back of my mind for many months now. I originally conceived of writing this back in February of 2011 but decided that the time was not right for it and waited. Had I written it back then I suspect the text would have been quite a bit different.
I was part of the original development team that wrote “The Daily” for News Corp.
When “The Daily” was released, we expected some issues with it. Every developer should expect issues with a 1.0 release. We knew that it was written under a tight deadline and that there were most certainly sharp edges that we had not identified. The application was about as well received as we could expect from the user base. Some people do not like Rupert Murdoch. Some people do not like his teams slant on the news. That was expected. He is good at polarizing his readership.
The response we got from the developer community was a complete surprise.
Back In The Day
One of the things that originally attracted me to being a Mac/Cocoa developer was the community. I remember, fondly, watching two direct competitors sitting across a table from one another trading code solutions. Both knew that the other person was going to add it to their code base and they shared that information anyway. Both developers knew that it was the other developer that was driving them to make a better product. There can be no first place without a second place. Having a close competitor helps drive us forward.
Likewise, going to a CocoaHeads meeting you would see senior developers, developers who have been doing this for decades, sitting next to developers who are just now wrapping their heads around retain/release. They weren’t pained but instead looking upon the younger developer with the fondness of remembering what it was like when they started. Perhaps a bit of envy of all the exciting things this new young developer is about to learn.
Introducing The iPhone
When the iPhone was introduced we were all very excited to start working with it. Cocoa on a mobile platform! We could not wait to get our hands on it. The community embraced it immediately.
At first you had to hack your phone to write code for it but we quickly got an SDK. The community consumed that SDK with a hunger. The forums were active, the boards were active, the blogs were hot. Everyone wanted to share the new cool thing they learned or share the pain they just went through so that, hopefully, no one else had to go through that pain. The community was alive and prosperous.
I do remember many conversations about what would happen to the community with this sudden influx of developers. Many conversations started over what to do about these developers invading our platform. When I was involved in those discussions my response was always the same; we would welcome them to the community and teach them how we work. We would show them how great it is over here and that we share our toys. We would welcome them knowing that they would become part of us; not the other way around.
For the most part that is what happened. A large portion of these developers joined us. They shared; many new blogs started up, new books were written and our NSCoder nights and CocoaHeads meetings grew. The community became stronger with this influx of new developers.
A Disturbing Trend
More recently, perhaps within the last year, there has been a disturbing trend in the community. Surprisingly, sadly, this trend has not come from the new developers but from some of the older grey beards. There has been a trend to “piss on” things written by other developers. A new app comes out, good or bad, and the claws come out. People are quick to blast it; the more press it gets, the more it gets blasted.
A new photo sharing idea that got a lot of VC money? Blast it!
A new game concept? Kill it!
An old idea rehashed in a new way? Destroy it! Burn them!
He got more press than me? He must die in a fire!
I would almost expect this from new developers who just joined the community. However it is not the new members of this community that are all aflame. Most likely they are looking at these ideas and seeing how they can apply them or if there is anything to learn from them.
Sadly though, it is the older, established, members of the community that are turning so hostile. Gone is the sharing and the live/let live attitude that once made this community so great. Quite a few members are just full of piss and vinegar.
You can say what you want about me. I do not hold myself above others and know that my code sucks more often than not. I tend to share that opinion of my code often. I do not share what I have learned to gain glory but to just enjoy the act of sharing. Sharing makes me feel good.
What saddens me is this new desire to attack things that are either new or just in the media. Does the application suck? Maybe. But to curse the developers who wrote it? Not cool.
We as developer must remember that we are not the target for 99% of the software that is written. We are not the final judge on what will or will not work. If anything, we are the last people that should have an opinion on what is good or bad. We should be the ones that step back and watch what the “normals” do with it. They determine the success or failure; not us.
Some Thoughts From The Trenches
Not everyone who reads this blog is an independent developer. Not everyone who reads this blog writes code to fit someone else’s goals so I would like to share a few points from someone who is an independent developer and writes code to meet the expectations from others.
Deadlines are a bitch
Rarely do I have the opportunity to set my own deadlines. Companies who hire development shops almost always have a deadline in mind before the first line of code is ever written. More often than not, they have a deadline in mind before they have all of the requirements defined.
We, as developers, do not get to move those deadlines without massive and dire consequences. Usually our only opportunity to move them is at the beginning and then by saying “No, Thank You” to the project. Moving a deadline mid project usually has financial consequences.
Non-Developers Think This Is Easy
Non-developers see that one new feature as trivial. They see that crash as obvious and do not understand what the hell is taking so long. Business people are non-developers. The people who sign checks are business people.
To go along with my point about deadlines, getting paid involves meeting the requirements of the project within the deadline. These are almost always at odds with each other. The requirements are far greater than can be fit within the deadline. The response from the business team is “add more people, make it happen”. We as developers know that adding more people will actually slow things down.
The First 90% Is Easy
Developers frequently look at a problem and in their first blush say “oh I see how that works, that is simple“. That is a trap my friends. Everything looks easy at first. My favorite recent example is the carousel of The Daily. It is trivial right? No, there are a huge number of dependencies and features and bells and whistle and edge cases that all work their way into that piece of the application. The core of moving images around on the screen is trivial. Anyone can do it in a couple of hours. However to complete all of the requirements? Months of work. Personally I am still not completely happy with it. Maybe with 6 more months of polish it will get to where I would like to see it.
Never underestimate the requirements that go into a piece of functionality. Don’t assume that the developers are incompetent if it doesn’t work or perform the way you expect it to. Chances are that there are requirements that you as a user are unaware of.
Software Development Is Not The Only Cost
This is my one hostile point in this post. Whoever thought the iOS developers got paid $30 Million on “The Daily” is a moron.
“The Daily” is a lot bigger than just writing iOS code. There is a huge editorial staff, there is a server team, there is office space, hardware, travel, the list goes on and on. The actual iOS code was a small fraction of the huge effort that was put into creating a digital only daily newspaper; the first of its kind by the way.
Doing Something First Sucks
Unless you are trying to get into some record book, the person who does something first is rarely remembered. He who does it best is often remembered fondly. When you are the first to do something you rarely are the best at it. This is just a simple fact of life. When you are the first to do something you are making shit up as you go along. You are guessing. You have no clue what is going to happen when you release. The first MP3 player? Shit. First Tablet? Horrible.
Being first means that you are going to be superseded. Either by improving on your design or by being replaced by another team that took your idea and ran with it. The iPod blew away the first MP3 player. The iPad blew away the first Tablet. I look forward to seeing who becomes the greatest digital only daily newspaper on a tablet. Maybe that will be The Daily via iteration or maybe it will be someone else.
“Be excellent to each other” — Bill & Ted’s Excellent Adventure
This should be the guiding principal of the Cocoa Developer Community in my not-so-humble opinion. It is one of the things that make it great. New people are welcomed and the older members are honored.
There is no reason to hate other development efforts. It does not matter if that developer is better or worse than you. It does not matter what that developer wrote. There is plenty of room for all of us.
Be excited by his or her success. His or her spotlight does not put you in darkness.
I look forward to seeing each of you next week in San Francisco. If you see me please feel free to say hi.
WWDC is once again upon us; be excellent to each other.
Hi, I’m new here. You may know me as @atomicbird on Twitter. Just a few days ago my book Core Data for iOS: Developing Data-Driven Applications for the iPad, iPhone, and iPod touch (co-written with the excellent Tim Isted) was published, and Matt invited me to contribute some Core Data tips to CIMGF. I’m going to start off discussing taking JSON data from a web service and converting it to Core Data storage. Along the way I’ll cover how to inspect managed objects to find out what attributes they have and what the attribute types are.
Publishing lead times being what they are, this post covers information not included in the book. (more…)
This is a short introductory article to welcome a new application to Zarra Studios.
We are involved in a lot of contract work and frequently our clients will give us video files. These files can be demos, mock ups, advertisements, etc.
As a developer on the move, I like to keep these with me and on my iPad so that I can review them whenever I want.
Of course, Client A does not want Client B to be able to accidentally see their files. Lawsuits happen that way.
To make this even more fun, everyone wants to borrow your iPad. Everyone wants to touch it and play with it. This increases the risk of the videos getting into the wrong hands.
From this, SecurVid was born.
SecurVid is designed to put videos behind a password lock. The videos are kept encrypted on disk and are not backed up to your computer that you sync your iPad with. This means that it is not designed to be a storage system for your videos but a protection for videos you need access to but don’t want everyone who borrows your iPad to see.
SecurVid has a lossy way to reset its password in case you forget it. Enter the wrong password three times and it will offer to reset for you. However that reset comes at a price; it will first delete all of your videos before offering to reset the password.
Once you are into SecurVid you can watch the videos you have already loaded naturally. You can also add more videos via iTunes as well as from any other application that is configured with file sharing. Therefore if a client emails you a video you can tap and press on the video file in mail on your iPad and load it into SecurVid.
Likewise you can export videos from SecurVid either for emailing or for loading into another application. You can even mark a video as “unprotected” and allow iTunes to see it next time you plug in your iPad.
This is the 1.0 release of SecurVid and has the core features that I/we needed in the application. However it is just the beginning for this application. As the application matures we will be adding additional features and continuing to release updates.
Because the 1.0 has only the core set of features we are offering it at an introductory price of $4.99. That price will remain until the next set of features are added. When that occurs we will increase the price up to the next appropriate level. However if you bought the 1.0 you will get these upgrades for free.
I know I mentioned we would talk about customizing the fetch requests, however, I have been working on some code related to the Active Record Fetching project, which I am renaming to MagicalRecord, that is also just as useful as fetching–threading.
Whenever most cocoa developers mention threading and Core Data in the same sentence, the reaction I see most often is that of mysticism and disbelief. For one, multithreaded programming in general is hard–hard to design correctly, hard to write correctly, and debugging threads is just asking for trouble. Introducing Core Data into that mix can seem like the straw that broke the camel’s back. However, by following a few simple rules and guidelines, and codifying them into a super simple pattern, one that may be familiar to you, we can achieve safer Core Data threading without the common headaches.