Top ipad Questions

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Ian Terrell

Are there any repositories around for open sourced iPhone and iPad components?

For instance, I have found myself needing to create several new types of table cells to mimic some of Apple's existing functionality (for instance, all the different types of table cells present in the Settings application). I can't imagine I'm alone here.

Where do you go to find open sourced reusable components, or do you just write and hoard your own?

Update: I know there are open source full projects around (see this question), but rummaging through them and picking and choosing still leads to significant duplication of effort.

Meta: There's a site for that!

There's a new nicely browsable list of iOS controls at

Ongoing List

Here are some libraries that I've found or been told about (even answered here) since asking this question:

  • CocoaHelpers -- Extensions to common classes
  • MBProgressHUD -- Replacement for the undocumented UIProgressHUD
  • cocos2d for iPhone -- 2d game engine
  • TouchCustoms -- Memory management, ratings, progress bars, more (GitHub Offline)
  • s7graphview -- Graphing
  • core-plot -- More graphing
  • HTFramework -- Reusable views
  • EGOTableViewPullRefresh -- Pull to refresh like Twitter (Tweetie 2)
  • PullToRefresh -- Another pull to refresh implementation
  • MGSplitViewController -- UISplitViewController replacement for the iPad
  • AQGridView -- A UITableView-style replacement that supports grids
  • DDActionHeaderView -- Combine the core concept of UIToolbar and UINavigationBar
  • DDAlertPrompt -- UIAlertView subclass providing UITextFields for user/password inputs
  • ASIHTTPRequest -- An easy to use wrapper around the CFNetwork API -- No Longer Active
  • AFNetworking -- Popular delightful networking library for iOS.
  • RestKit -- A modern framework for implementing RESTful web services clients on iOS.
  • ShareKit -- A quick way to integrate Twitter,Facebook, etc. into your app.
  • iDev Recipes - Open source code for the blog
  • QuickDialog - Easy way to create dialogs, either in Obj-C or JSON
  • Three20 -- Custom UI classes used in the Facebook application
Answered By: MattDiPasquale ( 112)

Here are some good iOS open-source libraries/frameworks & projects:

UI Libraries & Frameworks


  • General
  • REST
    • RestKit: Makes interacting with RESTful web services simple, fast and fun
    • HTTPRiot: A simple HTTP REST Library
    • ObjectiveResource: Makes interacting with Ruby on Rails applications dead simple
  • Sockets
    • AsyncSocket: TCP/IP socket networking library that wraps CFSocket and CFStream
    • Zimt: HTML5 Websockets

Core Data


Game Libraries & Frameworks

Testing Libraries & Frameworks

Martin Kool

Apple's iPad Mini is a smaller clone of the iPad 2 in more ways than we'd want. In JavaScript, the window.navigator object exposes the same values for the Mini and iPad 2. My tests so far to detect the difference have not lead to success.

Why is this important?

As the iPad Mini and iPad 2 screens are identical in pixels but vary in actual size (inches / centimeters), they vary in PPI (pixels per inch).

For web applications and games to offer a friendly user interface, certain elements are adjusted in size relative to a user's thumb or finger position, thus, we may want to scale certain images or buttons to provide for that better user experience.

Things I have tried so far (including some pretty obvious approaches):

  • window.devicepixelratio
  • CSS element width in cm unit
  • CSS media queries (such as resolution and -webkit-device-pixel-ratio)
  • SVG drawings in similar units
  • Doing all sorts of CSS webkit transforms for a set time and counting rendered frames with requestAnimFrame (I was hoping to detect a measurable difference)

I'm fresh out of ideas. How about you?

Update Thanks for the responses so far. I would like to comment on people voting against detecting iPad mini versus 2 as Apple has uhm, one guideline to rule them all. Okay, here's my reasoning why I feel it really makes all sense in the world to know if a person is using an iPad mini or a 2. And do with my reasoning what you like.

The iPad mini is not only a much smaller device (9.7 inch versus 7.9 inch), but its form factor allows for a different usage. The iPad 2 is usually held with two hands when gaming unless you're Chuck Norris. The mini is smaller, but it is also much lighter and allows for gameplay where you hold it in one hand and use another to swipe or tap or whatnot. As a game designer and developer myself, I'd just like to know if it's a mini so I can choose to provide the player with a different controlscheme if I want (for instance after A/B testing with a group of players).

Why? Well, it's a proven fact that the majority of users tend to go with the default settings, so leaving out a virtual thumbstick and putting some other tap-based control on the screen (just giving an arbitrary example here) when the player loads up the game for the first time is what I, and probably other game designers, would love to be able to do.

So IMHO this goes beyond the thick fingers / guidelines discussions and is just something Apple and all other vendors ought to do: allow us to uniquely identify your device and think different instead of following guidelines.

Answered By: Avi Marcus ( 204)

Play a stereo audio file and compare the accelerometer response when volume is high on the right channel and on the left channel - iPad2 had mono speakers whereas iPad Mini has built-in stereo speakers.

Need your help to gather the data please visit this page and help me collect data for this crazy idea. I don't have an iPad mini so I really need your help

Luke Mcneice

There has been many Questions recently about drawing PDF's.

Yes, you can render PDF's very easily with a UIWebView but this cant give the performance and functionality that you would expect from a good PDF viewer.

You can draw a PDF page to a CALayer or to a UIImage. Apple even have sample code to show how draw a large PDF in a Zoomable UIScrollview

But the same issues keep cropping up.

UIImage Method:

  1. PDF's in a UIImage don't optically scale as well as a Layer approach.
  2. The CPU and memory hit on generating the UIImages from a PDFcontext limits/prevents using it to create a real-time render of new zoom-levels.

CATiledLayer Method:

  1. Theres a significant Overhead (time) drawing a full PDF page to a CALayer: individual tiles can be seen rendering (even with a tileSize tweak)
  2. CALayers cant be prepared ahead of time (rendered off-screen).

Generally PDF viewers are pretty heavy on memory too. Even monitor the memory usage of apple's zoomable PDF example.

In my current project, I'm developing a PDF viewer and am rendering a UIImage of a page in a separate thread (issues here too!) and presenting it while the scale is x1. CATiledLayer rendering kicks in once the scale is >1. iBooks takes a similar double take approach as if you scroll the pages you can see a lower res version of the page for just less than a second before a crisp version appears.

Im rendering 2 pages each side of the page in focus so that the PDF image is ready to mask the layer before it starts drawing.Pages are destroyed again when they are +2 pages away from the focused page.

Does anyone have any insights, no matter how small or obvious to improve the performance/ memory handling of Drawing PDF's? or any other issues discussed here?

EDIT: Some Tips (Credit- Luke Mcneice,VdesmedT,Matt Gallagher,Johann):

  • Save any media to disk when you can.

  • Use larger tileSizes if rendering on TiledLayers

  • init frequently used arrays with placeholder objects, alternitively another design approach is this one

  • Note that images will render faster than a CGPDFPageRef

  • Use NSOperations or GCD & Blocks to prepare pages ahead of time.

  • call CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh); CGContextSetRenderingIntent(ctx, kCGRenderingIntentDefault); before CGContextDrawPDFPage to reduce memory usage while drawing

  • init'ing your NSOperations with a docRef is a bad idea (memory), wrap the docRef into a singleton.

  • Cancel needless NSOperations When you can, especially if they will be using memory, beware of leaving contexts open though!

  • Recycle page objects by doing pointer swaps or destroy unused views

  • Close any open Contexts as soon as you don't need them

  • on receiving memory warnings release and reload the DocRef and any page Caches

Other PDF Features:


Example projects

Answered By: VdesmedT ( 59)

I have build such kind of application using approximatively the same approach except :

  • I cache the generated image on the disk and always generate two to three images in advance in a separate thread.
  • I don't overlay with a UIImage but instead draw the image in the layer when zooming is 1. Those tiles will be released automatically when memory warnings are issued.

Whenever the user start zooming, I acquire the CGPDFPage and render it using the appropriate CTM. The code in - (void)drawLayer: (CALayer*)layer inContext: (CGContextRef) context is like :

CGAffineTransform currentCTM = CGContextGetCTM(context);    
if (currentCTM.a == 1.0 && baseImage) {
    //Calculate ideal scale
    CGFloat scaleForWidth = baseImage.size.width/self.bounds.size.width;
    CGFloat scaleForHeight = baseImage.size.height/self.bounds.size.height; 
    CGFloat imageScaleFactor = MAX(scaleForWidth, scaleForHeight);

    CGSize imageSize = CGSizeMake(baseImage.size.width/imageScaleFactor, baseImage.size.height/imageScaleFactor);
    CGRect imageRect = CGRectMake((self.bounds.size.width-imageSize.width)/2, (self.bounds.size.height-imageSize.height)/2, imageSize.width, imageSize.height);
    CGContextDrawImage(context, imageRect, [baseImage CGImage]);
} else {
    @synchronized(issue) { 
        CGPDFPageRef pdfPage = CGPDFDocumentGetPage(issue.pdfDoc, pageIndex+1);
        pdfToPageTransform = CGPDFPageGetDrawingTransform(pdfPage, kCGPDFMediaBox, layer.bounds, 0, true);
        CGContextConcatCTM(context, pdfToPageTransform);    
        CGContextDrawPDFPage(context, pdfPage);

issue is the object containg the CGPDFDocumentRef. I synchronize the part where I access the pdfDoc property because I release it and recreate it when receiving memoryWarnings. It seems that the CGPDFDocumentRef object do some internal caching that I did not find how to get rid of.


It has just come to light that the UIDevice uniqueIdentifier property is deprecated in iOS 5 and above. No alternative method or property appears to be available or forthcoming.

Many of our existing apps are tightly dependent on this property for uniquely identifying a particular device. Can anyone suggest any ideas how we might handle this problem going forward?

The suggestion from the documentation is...

Special Considerations

Do not use the uniqueIdentifier property. To create a unique identifier specific to your app, you can call the CFUUIDCreate function to create a UUID, and write it to the defaults database using the NSUserDefaults class.

... however this value won't be the same if a user uninstalls and re-installs the app.

Answered By: DarkDust ( 86)

A UUID created by CFUUIDCreate is unique if a user uninstalls and re-installs the app: you will get a new one each time.

But you might want it to be not unique, i. e. it should stay the same when the user uninstalls and re-installs the app. This requires a bit of effort, since the most reliable per-device-identifier seems to be the MAC address. You could query the MAC and use that as UUID.

Edit: One needs to always query the MAC of the same interface, of course. I guess the best bet is with en0. The MAC is always present, even if the interface has no IP/is down.

this is driving me crazy! I just upgraded to XCode 4 and for some reason my app won't run in the simulator or iOS device. It was working perfectly in XCode 3, but all of a sudden now when I press run the program stops at "Attaching to...". There doesn't seem to be any other info to help with this problem either. Any ideas?

For summary you can try following things to tackle the issue:

  1. Restart the simulator.
  2. Make sure that you haven't included the Info.plst file in your Building Phases -> Copy Bundle Resources.
  3. Resources folder added to the project as a folder reference (the blue folder icon). That caused the trouble, after adding the folder as a group the problem went away.
Answered By: Rob ( 95)

Fixed it!! Hopefully this helps some people avoid a very frustrating couple hours. I solved this by:

  1. Clicking on the project name in the left pane (at the very top). This will bring up a new menu to the right, something like the project/ target editors in XCode 3.
  2. Click on Build Settings up at the top.
  3. Under Packaging make sure your product name is the same for every build, and equal to whatever it says it's attaching to. Eg if XCode is Hanging at "Attaching to myLCBO" but your product name is "LCBO Finder" then it won't build. That was exactly my problem because I renamed my app half way through development.

Hope this helps!

Mihai Damian

On the subject of associating your iPhone app with file types.

In this informative question I learned that apps could be associated with custom URL protocols.

That was almost one year ago and since then Apple introduced 'Document Support' which goes a step further and allows apps to associate with file types. There is a lot of talk in the documentation about how to set up your app to launch other appropriate apps when it encounters an unknown file type. This means the association doesn't work out of the box for any app, like the URL protocol registering did.

This leads me to the question: have system apps like Safari or Mail implemented this system for choosing associated applications, or will they do nothing, as before?

Answered By: Brad Larson ( 228)

File type handling is new with iPhone OS 3.2, and is different than the already-existing custom URL schemes. You can register your application to handle particular document types, and any application that uses a document controller can hand off processing of these documents to your own application.

For example, my application Molecules (for which the source code is available) handles the .pdb and .pdb.gz file types, if received via email or in another supported application.

To register support, you will need to have something like the following in your Info.plist:

        <string>Molecules Structure File</string>

Two images are provided that will be used as icons for the supported types in Mail and other applications capable of showing documents. The LSItemContentTypes key lets you provide an array of Uniform Type Identifiers (UTIs) that your application can open. For a list of system-defined UTIs, see Apple's Uniform Type Identifiers Reference. Even more detail on UTIs can be found in Apple's Uniform Type Identifiers Overview. Those guides reside in the Mac developer center, because this capability has been ported across from the Mac.

One of the UTIs used in the above example was system-defined, but the other was an application-specific UTI. The application-specific UTI will need to be exported so that other applications on the system can be made aware of it. To do this, you would add a section to your Info.plist like the following:

        <string>Molecules Structure File</string>

This particular example exports the com.sunsetlakesoftware.molecules.pdb UTI with the .pdb file extension, corresponding to the MIME type chemical/x-pdb.

With this in place, your application will be able to handle documents attached to emails or from other applications on the system. In Mail, you can tap-and-hold to bring up a list of applications that can open a particular attachment.

When the attachment is opened, your application will be started and you will need to handle the processing of this file in your -application:didFinishLaunchingWithOptions: application delegate method. It appears that files loaded in this manner from Mail are copied into your application's Documents directory under a subdirectory corresponding to what email box they arrived in. You can get the URL for this file within the application delegate method using code like the following:

NSURL *url = (NSURL *)[launchOptions valueForKey:UIApplicationLaunchOptionsURLKey];

Note that this is the same approach we used for handling custom URL schemes. You can separate the file URLs from others by using code like the following:

if ([url isFileURL])
    // Handle file being passed in
    // Handle custom URL scheme