iOS SDK and SQLite: Building Data-Driven Apps
Illustration by Don Barnett

iOS SDK and SQLite: Building Data-Driven Apps

with Bill Weinman

Video: Delegating back to the parent view

Now that we're parsing the feed header, we need to send data back to the FeedsTableViewController for processing. Remember, the AddViewController object is a modal dialog. What we want to do is little processing as possible there. We created a small delegate protocol for communicating with the FeedsTableViewController, and now we're going to use it. So, let's start by making a working copy of addView-04, and I'm going to use my -done version. You can use the one that you worked on in the last movie if you like, if you've been following along. And I'm just going to call this addView-05, and I'm going to open it in Xcode by double-clicking on the Xcode project file.
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  1. 8m 29s
    1. Welcome
      57s
    2. Exercise files
      2m 17s
    3. Course overview
      3m 4s
    4. Application overview
      2m 11s
  2. 14m 49s
    1. Prototyping in a testbed
      1m 27s
    2. Building the view controller
      3m 45s
    3. Coding the testbed
      7m 56s
    4. Using the testbed
      1m 41s
  3. 37m 49s
    1. Understanding SQLite in iOS
      1m 41s
    2. Creating an Objective-C interface for SQLite
      9m 57s
    3. Testing the BWDB interface in the sandbox
      7m 1s
    4. Designing a database schema
      8m 7s
    5. Supporting the application with a specific interface
      7m 7s
    6. Using C pointers with automatic reference counting (ARC)
      3m 56s
  4. 21m 18s
    1. Understanding the table view
      1m 33s
    2. Creating the view controller
      6m 39s
    3. Reading from the database
      13m 6s
  5. 33m 50s
    1. Understanding the parsing process
      1m 57s
    2. Creating the item view controller
      12m 25s
    3. Reading data from the internet
      5m 30s
    4. Parsing the feed with NSXMLParser
      8m 2s
    5. Updating the item view with the feed items
      5m 56s
  6. 40m 14s
    1. Understanding the modal view
      1m 47s
    2. Constructing the view controller
      15m 5s
    3. Finding a feed link in a web page
      8m 55s
    4. Parsing the feed with NSXMLParser
      5m 4s
    5. Delegating back to the parent view
      6m 11s
    6. Deleting feeds
      3m 12s
  7. 21m 5s
    1. Creating the web view class
      12m 33s
    2. Coding the web view
      5m 25s
    3. Viewing pages in Safari
      3m 7s
  8. 14m 3s
    1. Understanding the iOS preferences system
      1m 23s
    2. Creating the preferences plist in Xcode
      7m 20s
    3. Reading preferences in your application
      5m 20s
  9. 6m 15s
    1. Adding pull-to-refresh functionality
      2m 34s
    2. Implementing the pull-to-refresh gesture for iOS 6
      3m 41s
  10. 27m 1s
    1. Understanding split view
      1m 4s
    2. Coding the table views
      11m 24s
    3. Implementing the iPad detail view
      6m 35s
    4. Implementing the iPad modal view
      7m 58s
  11. 35s
    1. Goodbye
      35s

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Watch the Online Video Course iOS SDK and SQLite: Building Data-Driven Apps
3h 45m Intermediate Jan 16, 2013

Viewers: in countries Watching now:

The iOS software development kit (SDK) includes the popular SQLite library, a lightweight yet powerful relational database engine that is easily embedded into an application. In this course, Bill Weinman teaches you how to build an RSS reader for iOS devices, integrating XML data and a streamlined interface. He explains how to use the SQLite database, display information in a table view, code view controllers, and create a preferences pane for your app. The resulting application is optimized for all iPhone and iPad displays.

Topics include:
  • Prototyping the app
  • Coding and working with a testbed
  • Creating an Objective-C interface for SQLite
  • Designing a database schema
  • Creating the view controllers
  • Reading and writing to the database
  • Parsing the RSS feed with NSXMLParser
  • Updating the item view with feed items
  • Implementing the pull to refresh gesture for iOS 6
  • Creating a universal application with multiple views
Subject:
Developer
Software:
iOS
Author:
Bill Weinman

Delegating back to the parent view

Now that we're parsing the feed header, we need to send data back to the FeedsTableViewController for processing. Remember, the AddViewController object is a modal dialog. What we want to do is little processing as possible there. We created a small delegate protocol for communicating with the FeedsTableViewController, and now we're going to use it. So, let's start by making a working copy of addView-04, and I'm going to use my -done version. You can use the one that you worked on in the last movie if you like, if you've been following along. And I'm just going to call this addView-05, and I'm going to open it in Xcode by double-clicking on the Xcode project file.

Now, if we notice in our addView.h file, we have this protocol that we define, this RSSAddViewControllerDelegate protocol. And it has three methods in it, and those methods are actually going to be run in the FeedsTableViewController. So, the FeedsTableViewController is going to be the delegate for this delegate protocol. And you'll notice right here we have this property which is called delegate, which is of type id with this delegate protocol. And you'll notice, back here in our haveFeed method, we actually call haveAddViewRecord, which is one of our delegate methods, haveAddViewRecord on that delegate.

So, I'm going to uncomment this, and I'm going to uncomment this to dismiss the view controller. And now we need to set this delegate property here, and that gets set from the FeedsTableViewController. Now, in the FeedsTableViewController, this is going to be a set in our segue, because our segue is what happens when we press on that Plus button. Then we get the segue to the AddViewModelController and the model controller, it slides up the screen with that animation. It covers the entire screen. And before we can start handling this in the segue, we need to know about it, so we're going to come in here to our controller.h, and I'm going to import our AddViewController header. And I'm going to come down here to our interface which defines the class type and the parent class type.

I'm going to declare this protocol type as well. So, this is our RSSAddViewControllerDelegate. So, I'll save here, and I'm going to come back over here to the end file, and now we can handle this other segue. Now, if you remember, we come over here to the iPhone storyboard--and I'm just going to display this right side real quick. So, this is the segue here, and it has the segue identifier, SegueToAddView, so I'm just going to copy that so that I can paste it in and know that I have spelled it correctly.

Over here, I'm going to say else if (segue. identifier isEqualToString:@"SegueToAddView"), and then I'm going to declare a pointer to the BWRSS AddViewController class. And that's our destinationViewController in the segue, so I can just say destinationViewController. Now that we have a pointer to that destinationViewController, I can set its delegate to this FeedsTableViewController.

Now, when the AddViewController calls something on its delegate, it's going to be calling it on this controller, the BWRSS FeedsTableViewController. This controller is declared to handle that protocol. You notice up here it says that our protocol is not implemented yet. That's because we haven't yet added those methods. And so I'm going to add those methods right here before the database methods. And we'll come out here to the Finder, and we'll open our 05-methods.txt file, and there they are. I'm going to select all and copy and come back into Xcode and paste them in right there. Command+S to save.

So now, our AddViewController, when it has a feed, it's going to call this haveAddViewRecord with the feedRecord. Here in our FeedsTableViewController, here it is, and it's going to get that record, it's going to sign it to this new feed variable. And so we need to do one more thing. When that gets assigned, we need to come back up here in our view stuff, and I'm going to come down here and I'm going to declare a viewDidAppear, and if (newFeed), (self loadNewFeed).

If we come down here and we see what loadNewFeed does, it goes ahead and either inserts it in the database or updates it in the database, and it does this nice animation reveal. We'll see what that looks like right now. We're going to go ahead and run this in the simulator. So now, let's go ahead and add that CNN feed-- CNN.com--and I'll press Add, and you see it has that nice little horizontal reveal. You notice it's using this UITableViewRowAnimationLeft, and it's using the same one here when it's updated.

So, if I go ahead and put in that same URL, you'll notice that it comes in here and it just rotates it into place like that. So, if we come back up here to our AddViewControllerDelegate method, you'll notice here that there is URL errors and there is RSS errors. So, if I come back here to the simulator-- and let's just put in something that doesn't have a feed, like for instance music.bw.org I know that one doesn't have a feed--and it says, RSS Error did not find a feed.

So, that's this haveAddViewRecord message. And for an error, if I put in a URL that just doesn't exist, like x.y, and click Add, it says, URL Error, a server with a specified host name could not be found. So, those are these two messages here. So now the feed is being properly added and updated, and it's all working quite well. The delegate protocol that we created is very easy to use, and it's also working well. This allows the modal view to do its job while passing its results back to the main view so that it can do its job. It's all very neat and tidy.

Find answers to the most frequently asked questions about iOS SDK and SQLite: Building Data-Driven Apps .


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Q: Why is the RSSDB library in the exercise files different than the one in the videos?

A: The RSSDB library had to be updated to work around a bug in the iOS 7 SDK.

There is a bug in the iOS 7 SDK that prevents the BWDB fast enumeration implementation from working on a device. The symptom is code that runs fine on the emulator, but not on a device. iOS devices use an ARM processor, while the emulator runs on your Mac's Intel processor. This points to the LLVM ARM code generator as the source of the bug. Because the bug appears to be in the LLVM compiler, it may be some time before it is fixed.

As a workaround we have changed the getFeedIDs and getItemIDs methods in the RSSDB library so they don't use Objective C fast enumeration. 

Please note that this same bug also affects some of the BWDB testbed code in Chapter 2. The result is that it will run on the emulator but not on a device.

Q: After upgrading to Xcode 5.1 I get an error that says:

"Used type va_list (aka_builtin_va_list) where arithmetic or pointer type is required"

A: Please download the exercise files again to get the latest version of the BWDB library.
 
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