iOS: Deselecting UITableViewCell with AutoLayout

You'll notice that when deselecting a customized UITableViewCell using tableView-deselectRowAtIndexPath:animated: method inside tableView-didSelectRowAtIndexPath: method is that its contentView gets misplaced. It's probably halfway up the cell. I really think there's a bug on this area for Apple to adress. In the meantime, to work around this bug, you only need to replace the tableView-deselectRowAtIndexPath:animated: method call with tableView-reloadData. Yes it is. And for as long you don't have such a complicated tableView and cell structure, worry not about the performance.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
  ... dance right here ...
  [tableView reloadData];
}

UICollectionView: Paging for Smaller Width Cells

In the application I'm working on, there's a 320pt wide horizontal-only scrolling UICollectionView with varied content width depending on the number of items. The UICollectionViewCell subclass or itemView being used here has a width of 250pt enough to let the next itemView peak just a little bit. And I need to show one itemView at a time by snapping to the closest one.

// NOTE: This delegate method requires you to disable UICollectionView's `pagingEnabled` property.
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
                     withVelocity:(CGPoint)velocity
              targetContentOffset:(inout CGPoint *)targetContentOffset {
 
  CGPoint point = *targetContentOffset;  

  UICollectionViewFlowLayout *layout = (UICollectionViewFlowLayout *)self.collectionView.collectionViewLayout;
 
  // This assumes that the values of `layout.sectionInset.left` and 
  // `layout.sectionInset.right` are the same with `layout.minimumInteritemSpacing`. 
  // Remember that we're trying to snap to one item at a time. So one 
  // visible item comprises of its width plus the left margin.
  CGFloat visibleWidth = layout.minimumInteritemSpacing + layout.itemSize.width;

  // It's either we go forwards or backwards. 
  int indexOfItemToSnap = round(point.x / visibleWidth);

  // The only exemption is the last item. 
  if (indexOfItemToSnap + 1 == [self.collectionView numberOfItemsInSection:0]) { // last item
    *targetContentOffset = CGPointMake(self.collectionView.contentSize.width -
                                       self.collectionView.bounds.size.width, 0);
  } else {
    *targetContentOffset = CGPointMake(indexOfItemToSnap * visibleWidth, 0);
  }
}

Embed Youtube Video using iFrame JS Player API

Here's the code to embed Youtube video using their new iFrame Javascript Player API. This is the piece of code I also used to embed YouTube video in my iOS application. Also, it is possible to play it inline. Not the typical fullscreen playback.

Read more about the iFrame Player API Reference.

It's also worth mentioning that on iOS6 devices, autoplay just doesn't work anymore. Apple added this restriction to save user's bandwidth. Read more about User Control of Downloads Over Cellular Networks.

UPDATE 2014-10-29
- Use this instead: https://developers.google.com/youtube/v3/guides/ios_youtube_helper

iOS: Stopping a chain of Block-based animations

This can easily be done using one line of code and given you're using either [UIView animateWithDuration:animations:] or [UIView animateWithDuration:animations:completion], or both of them interchangeably.

[someView.layer removeAllAnimations]

But what if another variant of these methods is also in the mix? This method is [UIVIew animateWithDuration:delay:options:animations:completion].

What happens is that, whatever is in the completion block of this method, it still is executed right after calling [CALayer removeAllAnimations]. So the right thing to do here is always check for the value of the Boolean argument, finished. If it evaluates to True, then let the rest of the code continue. Otherwise, stop. Also, make sure to include UIViewAnimationOptionAllowUserInteraction in the options parameter.

iOS: Unrecognized selector sent to class...

There are several reasons why this could happen. One of this is when adding a static Objective-C Library into your project. While compiling the app may seem to work fine, the actual code using the library may encounter this exception. The simple solution to this is to add a linker flag -all_load to your project's Targets->YourProject->Build Settings->Linking->Other Linker Flags. 

Read Apple's technical note about this issue here.

IMPORTANT: For 64-bit and iPhone OS applications, there is a linker bug that prevents -ObjC from loading objects files from static libraries that contain only categories and no classes. The workaround is to use the -all_load or -force_load flags. -all_load forces the linker to load all object files from every archive it sees, even those without Objective-C code. -force_load is available in Xcode 3.2 and later. It allows finer grain control of archive loading. Each -force_load option must be followed by a path to an archive, and every object file in that archive will be loaded.

Shared Twitter Application among Developers

Is it possible? Answer is, NO. There's no way you can add multiple developer accounts to an application. According to Twitter, "this is not supported at this time and only one user account can maintain an application record".

Also worth mentioning, it is possible to transfer application's ownership to another user account. Details here.

Effectively render a Drop Shadow on a UIView subclass

Adding a drop shadow to your UIView subclass is as easy as the following code.

UIView *customView = [[UIView alloc] init];
...
customView.layer.shadowColor    = [[UIColor lightGrayColor] CGColor];
customView.layer.shadowOffset   = CGSizeMake(1, 1);
customView.layer.shadowOpacity  = 1.0;
customView.layer.shadowRadius   = 2.0; 
... 

While the common use case of such trick is on rendering stationary views, and no doubt it works perfectly that way, placing them inside a scrollable view like UISrollView or UITableView yields a different feel - it lags a bit when scrolling. So the way to solve this issue and keep them scrolling smoothly is to make use of UIBezierPath. You create an instance of this based on the `bounds` of the receiving view. Then set it as the `shadowPath` of the view's layer object.

UIBezierPath *path  = [UIBezierPath bezierPathWithRect:customView.bounds];
customView.layer.shadowPath = [path CGPath];

Now let's modify our base code to include the bezier path.

UIView *customView = [[UIView alloc] init];
...
UIBezierPath *path  = [UIBezierPath bezierPathWithRect:customView.bounds];
customView.layer.shadowPath = [path CGPath];

customView.layer.shadowColor    = [[UIColor lightGrayColor] CGColor];
customView.layer.shadowOffset   = CGSizeMake(1, 1);
customView.layer.shadowOpacity  = 1.0;
customView.layer.shadowRadius   = 2.0; 
... 

Trouble setting up iOS Push Notifications (APNS)

The following is caused by an invalid or outdated Provisioning Profile.

• "no valid aps-environment entitlement found for application" (NSError displayed using NSLog)
• "The entitlements specified in your application’s Code Signing Entitlements file do not match those specified in your provisioning profile" (displayed in Organizer window)

Take note that even if you're just updating an existing App ID in the Provisioning Portal, say you've just enabled this app's Push Notifications, you would also need to modify and re-submit the application's current Provisioning Profile (make sure that your test device is included in the list). After that, download and install this file, update Code Signing Identity section of your project's Build Settings to reflect the new profile (in xcode of course), then you're on to the next case.

Add a Group-By Scope to Yii's CActiveRecord Subclass

Yii Framework allows for named scopes to be added to a CActiveRecord's subclass (you can read more about this here). This also makes it more convenient to filter models based on a predetermined criteria. You can chain them with any filter methods of that class, and ultimately the CDbCriteria methods like `findAll()`.

To site an example, let's have a database table named `animals`. It also has the following fields: id, name, and classification. Let's fill this up with some data. I know this can still be normalized, but let's just leave it like this for the sake of simplicity.

[ 1, 'Eagle',     'Bird']
[ 2, 'Peacock',   'Bird']
[ 3, 'Kangaroo',  'Mammal']
[ 4, 'Dog',       'Mammal']
[ 5, 'Horse',     'Mammal']
[ 6, 'Snake',     'Reptile']
[ 7, 'Turtle',    'Reptile']
[ 8, 'Lizard',    'Reptile']
[ 9, 'Crocodile', 'Reptile']
[10, 'Spider',    'Arthropods']

Now, assuming we're asked to provide a summary of classifications, like return a list of classifications with a number of animals in each of them. This is how our sql query looks like if nothing else is added in the criteria.

SELECT t.classification, COUNT(*) AS animalCount
  FROM `animals` AS t
  GROUP BY t.classification
  ORDER BY animalCount DESC;

If you try to run this query, the result looks something like this.

[Reptile,     4]
[Mammal,      3]
[Bird,        2]
[Arthropods,  1]

Let's assume that we've created a model class named `Animal`, which represents our `animals` db table and has the following method which does the same thing as the aforementioned sql query. It looks like the following:

public function scopes()
{
  return array(
    'groupByClass' => array(
      'group'   => 't.classification',
      'select'  => 't.classification, COUNT(*) as animalCount',
      'order'   => 'animalCount DESC',
    ),
  );
}

This is the overriden method coming from CActiveRecord. To use this, we simply type:

Animal::method()->groupByClass()->findAll();

Then we get the same result:

[Reptile,     4]
[Mammal,      3]
[Bird,        2]
[Arthropods,  1]

You must be wondering how the heck I'm supposed to access `animalCount` alias. Well for that, we can simply add a special property. That would of course be of the same name, which is `animalCount`.

So there you have it.

Facebook IFrame App in Safari

You don't really need cookies to make your Facebook IFrame app work in Safari browser. I remember two years ago, to make Page Tab applications work in Safari, you only need to make use of this trick. I won't be explaining it in details here.

Just recently, I was asked to do this new Fb project that's intended for Page Tab, which now is an iFrame-only platform. I've been developing it using Chrome browser. And when I finally get to test it on Safari, unsurprisingly, it's the same old scenario. What's worse is that the old trick won't work anymore (you better read this).

This app relies so much on Javascript. And instead of deploying several php pages, I only need to come up with a startup page which when loaded on the iFrame, loads the rest of the required scripts. Other pages are dynamically constructed using html fragments that are parsed by a templating script. So most of the Client-Server transactions are done asynchronously. And with Safari continously blocking third-party cookies, it just doesn't work.

After hours of googling for answers, I turned to Facebook's PHP SDK. I found out that it doesn't really require you to use cookies after all (now at 3.1.1). If you take a look at `BaseFacebook` class, particularly the `getSignedRequest` method, you'll see that it first checks the request parameter for Signed Request data (they used to have `session` before this).

...
public function getSignedRequest() {
  if (!$this->signedRequest) {
    if (isset($_REQUEST['signed_request'])) {
      $this->signedRequest = $this->parseSignedRequest(
        $_REQUEST['signed_request']);
    } else if (isset($_COOKIE[$this->getSignedRequestCookieName()])) {
      $this->signedRequest = $this->parseSignedRequest(
        $_COOKIE[$this->getSignedRequestCookieName()]);
    }
  }
  return $this->signedRequest;
}
...

With this in mind, it's possible to send `signed_request` data along with an Ajax request which the PHP SDK can use to determine the user and for your app to verify as well. I use FB.getLoginStatus to acquire a copy of this data. This of course assumes that the user has already authorized your app. Otherwise you'll have to let him do so.

The following example uses jQuery's `$.ajax`.

...
$.ajax({
  url: BACKEND_LINK_HERE,
  type: 'POST',
  data: {
    signed_request: 'sOm3ReA||yLo0ooooooo...oooooooooNgT3xtHeR3',
    another_data: 12345
  }
})
...

So that's it. You need to make sure you have a valid `signed_request` data each time a user interacts with your application. Don't even think about storing it because the access token contained will soon expire which then deems it useless (about 2.5 hours from the moment the user interacted with your app). Yes that's right. And just to let you know, `offline_access` is no longer supported.

Here's a Facebook article about handling invalid and expired access tokens in case you're interested.


Related posts:

• Facebook FB.getLoginStatus() Not Working
• Grab the Picture of a Facebook Graph Object
• Facebook iOS SDK: Let users Connect & Login with FB