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I have a UILabel with space for two lines of text. Sometimes, when the text is too short, this text is displayed in the vertical center of the label.

How do I vertically align my text to be always at the top of the UILabel?

alt text

Answered By: nevan king ( 850)

There's no way to set the vertical align on a UILabel, but you can get the same effect by changing the label's frame. I've made my labels orange so you can see clearly what's happening.

Here's the quick and easy way to do this:

    [myLabel sizeToFit];

sizeToFit to squeeze a label

If you have a label with longer text that will make more than one line, set numberOfLines to 0 (zero here means an unlimited number of lines).

    myLabel.numberOfLines = 0;
    [myLabel sizeToFit];

Longer label text with sizeToFit

Longer Version

I'll make my label in code so that you can see what's going on. You can set up most of this in Interface Builder too. My setup is a View Based App with a background image I made in Photoshop to show margins (20 points). The label is an attractive orange color so you can see what's going on with the dimensions.

- (void)viewDidLoad
    [super viewDidLoad];

    // 20 point top and left margin. Sized to leave 20 pt at right.
    CGRect labelFrame = CGRectMake(20, 20, 280, 150);
    UILabel *myLabel = [[UILabel alloc] initWithFrame:labelFrame];
    [myLabel setBackgroundColor:[UIColor orangeColor]];

    NSString *labelText = @"I am the very model of a modern Major-General, I've information vegetable, animal, and mineral";
    [myLabel setText:labelText];

    // Tell the label to use an unlimited number of lines
    [myLabel setNumberOfLines:0];
    [myLabel sizeToFit];

    [self.view addSubview:myLabel];

Some limitations of using sizeToFit come into play with center- or right-aligned text. Here's what happens:

    // myLabel.textAlignment = UITextAlignmentRight;
    myLabel.textAlignment = UITextAlignmentCenter;

    [myLabel setNumberOfLines:0];
    [myLabel sizeToFit];

enter image description here

The label is still sized with a fixed top-left corner. You can save the original label's width in a variable and set it after sizeToFit, or give it a fixed width to counter these problems:

    myLabel.textAlignment = UITextAlignmentCenter;

    [myLabel setNumberOfLines:0];
    [myLabel sizeToFit];

    CGRect myFrame = myLabel.frame;
    // Resize the frame's width to 280 (320 - margins)
    // width could also be myOriginalLabelFrame.size.width
    myFrame = CGRectMake(myFrame.origin.x, myFrame.origin.y, 280, myFrame.size.height);
    myLabel.frame = myFrame;

label alignment

Note that sizeToFit will respect your initial label's minimum width. If you start with a label 100 wide and call sizeToFit on it, it will give you back a (possibly very tall) label with 100 (or a little less) width. You might want to set your label to the minimum width you want before resizing.

Correct label alignment by resizing the frame width

Some other things to note:

Whether lineBreakMode is respected depends on how it's set. UILineBreakModeTailTruncation (the default) is ignored after sizeToFit, as are the other two truncation modes (head and middle). UILineBreakModeClip is also ignored. UILineBreakModeCharacterWrap works as usual. The frame width is still narrowed to fit to the rightmost letter.

My Original Answer (for posterity/reference):

This uses the NSString method sizeWithFont:constrainedToSize:lineBreakMode: to calculate the frame height needed to fit a string, then sets the origin and width.

Resize the frame for the label using the text you want to insert. That way you can accommodate any number of lines.

CGSize maximumSize = CGSizeMake(300, 9999);
NSString *dateString = @"The date today is January 1st, 1999";
UIFont *dateFont = [UIFont fontWithName:@"Helvetica" size:14];
CGSize dateStringSize = [dateString sizeWithFont:dateFont 

CGRect dateFrame = CGRectMake(10, 10, 300, dateStringSize.height);

self.dateLabel.frame = dateFrame;

This page has some different code for the same solution:

I've noticed that there are many questions about how to handle UIImage objects, especially in conjunction with UIImagePickerController and then displaying it in a view (usually a UIImageView). Here is a collection of common questions and their answers. Feel free to edit and add your own.

I obviously learnt all this information from somewhere too. Various forum posts, StackOverflow answers and my own experimenting brought me to all these solutions. Credit goes to those who posted some sample code that I've since used and modified. I don't remember who you all are - but hats off to you!

How Do I Select An Image From the User's Images or From the Camera?

You use UIImagePickerController. The documentation for the class gives a decent overview of how one would use it, and can be found here.

Basically, you create an instance of the class, which is a modal view controller, display it, and set yourself (or some class) to be the delegate. Then you'll get notified when a user selects some form of media (movie or image in 3.0 on the 3GS), and you can do whatever you want.

My Delegate Was Called - How Do I Get The Media?

The delegate method signature is the following:

- (void)imagePickerController:(UIImagePickerController *)picker
didFinishPickingMediaWithInfo:(NSDictionary *)info;

You should put a breakpoint in the debugger to see what's in the dictionary, but you use that to extract the media. For example:

UIImage* image = [info objectForKey:UIImagePickerControllerOriginalImage];

There are other keys that work as well, all in the documentation.

OK, I Got The Image, But It Doesn't Have Any Geolocation Data. What gives?

Unfortunately, Apple decided that we're not worthy of this information. When they load the data into the UIImage, they strip it of all the EXIF/Geolocation data. But, see the answer to the next question for a way to get at the original image data (on iOS 4+)

Can I Get To The Original File Representing This Image on the Disk?

As of iOS 4, you can, but it's very annoying. Use the following code to get an AssetsLibrary URL for the image, and then pass the URL to assetForURL:resultBlock:failureBlock:

NSURL *referenceURL = [info objectForKey:UIImagePickerControllerReferenceURL];
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library assetForURL:referenceURL resultBlock:^(ALAsset *asset) {
    // code to handle the asset here
} failureBlock:^(NSError *error) {
    // error handling
[library release];

It's annoying because the user is asked if your application can access your current location, which is rather confusing since you are actually trying to access the user's photo library. Unless you're actually trying to get at the EXIF location data, the user is going to be a bit confused.

Make sure to include the AssetsLibrary framework to make this work.

How Can I Look At The Underlying Pixels of the UIImage?

Since the UIImage is immutable, you can't look at the direct pixels. However, you can make a copy. The code to this looks something like this:

UIImage* image = ...; // An image
NSData* pixelData = (NSData*) CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage));
unsigned char* pixelBytes = (unsigned char *)[pixelData bytes];

// Take away the red pixel, assuming 32-bit RGBA
for(int i = 0; i < [pixelData length]; i += 4) {
        pixelBytes[i] = 0; // red
        pixelBytes[i+1] = pixelBytes[i+1]; // green
        pixelBytes[i+2] = pixelBytes[i+2]; // blue
        pixelBytes[i+3] = pixelBytes[i+3]; // alpha

However, note that CGDataProviderCopyData provides you with an "immutable" reference to the data - meaning you can't change it (and you may get a BAD_ACCESS error if you do). Look at the next question if you want to see how you can modify the pixels.

How Do I Modify The Pixels of the UIImage?

The UIImage is immutable, meaning you can't change it. Apple posted a great article on how to get a copy of the pixels and modify them, and rather than copy and paste it here, you should just go read the article.

Once you have the bitmap context as they mention in the article, you can do something similar to this to get a new UIImage with the modified pixels:

CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage* newImage = [UIImage imageWithCGImage:ref];

Do remember to release your references though, otherwise you're going to be leaking quite a bit of memory.

After I Select 3 Images From The Camera, I Run Out Of Memory. Help!

You have to remember that even though on disk these images take up only a few hundred kilobytes at most, that's because they're compressed as a PNG or JPG. When they are loaded into the UIImage, they become uncompressed. A quick over-the-envelope calculation would be:

width x height x 4 = bytes in memory

That's assuming 32-bit pixels. If you have 16-bit pixels (some JPGs are stored as RGBA-5551), then you'd replace the 4 with a 2.

Now, images taken with the camera are 1600 x 1200 pixels, so let's do the math:

1600 x 1200 x 4 = 7,680,000 bytes = ~8 MB

8 MB is a lot, especially when you have a limit of around 24 MB for your application. That's why you run out of memory.

OK, I Understand Why I Have No Memory. What Do I Do?

There is never any reason to display images at their full resolution. The iPhone has a screen of 480 x 320 pixels, so you're just wasting space. If you find yourself in this situation, ask yourself the following question: Do I need the full resolution image?

If the answer is yes, then you should save it to disk for later use.

If the answer is no, then read the next part.

Once you've decided what to do with the full-resolution image, then you need to create a smaller image to use for displaying. Many times you might even want several sizes for your image: a thumbnail, a full-size one for displaying, and the original full-resolution image.

OK, I'm Hooked. How Do I Resize the Image?

Unfortunately, there is no defined way how to resize an image. Also, it's important to note that when you resize it, you'll get a new image - you're not modifying the old one.

There are a couple of methods to do the resizing. I'll present them both here, and explain the pros and cons of each.

Method 1: Using UIKit

+ (UIImage*)imageWithImage:(UIImage*)image scaledToSize:(CGSize)newSize;
    // Create a graphics image context

    // Tell the old image to draw in this new context, with the desired
    // new size
    [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

    // Get the new image from the context
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();

    // End the context

    // Return the new image.
    return newImage;

This method is very simple, and works great. It will also deal with the UIImageOrientation for you, meaning that you don't have to care whether the camera was sideways when the picture was taken. However, this method is not thread safe, and since thumbnailing is a relatively expensive operation (approximately ~2.5s on a 3G for a 1600 x 1200 pixel image), this is very much an operation you may want to do in the background, on a separate thread.

Method 2: Using CoreGraphics

+ (UIImage*)imageWithImage:(UIImage*)sourceImage scaledToSize:(CGSize)newSize;
    CGFloat targetWidth = newSize.width;
    CGFloat targetHeight = newSize.height;

    CGImageRef imageRef = [sourceImage CGImage];
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

    if (bitmapInfo == kCGImageAlphaNone) {
        bitmapInfo = kCGImageAlphaNoneSkipLast;

    CGContextRef bitmap;

    if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
        bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    } else {
        bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);


    if (sourceImage.imageOrientation == UIImageOrientationLeft) {
        CGContextRotateCTM (bitmap, M_PI_2); // + 90 degrees
        CGContextTranslateCTM (bitmap, 0, -targetHeight);

    } else if (sourceImage.imageOrientation == UIImageOrientationRight) {
        CGContextRotateCTM (bitmap, -M_PI_2); // - 90 degrees
        CGContextTranslateCTM (bitmap, -targetWidth, 0);

    } else if (sourceImage.imageOrientation == UIImageOrientationUp) {
        // NOTHING
    } else if (sourceImage.imageOrientation == UIImageOrientationDown) {
        CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
        CGContextRotateCTM (bitmap, -M_PI); // - 180 degrees

    CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage* newImage = [UIImage imageWithCGImage:ref];


    return newImage; 

The benefit of this method is that it is thread-safe, plus it takes care of all the small things (using correct color space and bitmap info, dealing with image orientation) that the UIKit version does.

How Do I Resize and Maintain Aspect Ratio (like the AspectFill option)?

It is very similar to the method above, and it looks like this:

+ (UIImage*)imageWithImage:(UIImage*)sourceImage scaledToSizeWithSameAspectRatio:(CGSize)targetSize;
    CGSize imageSize = sourceImage.size;
    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;
    CGFloat scaleFactor = 0.0;
    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;
    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

    if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;

        if (widthFactor > heightFactor) {
            scaleFactor = widthFactor; // scale to fit height
        else {
            scaleFactor = heightFactor; // scale to fit width

        scaledWidth  = width * scaleFactor;
        scaledHeight = height * scaleFactor;

        // center the image
        if (widthFactor > heightFactor) {
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
        else if (widthFactor < heightFactor) {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

    CGImageRef imageRef = [sourceImage CGImage];
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

    if (bitmapInfo == kCGImageAlphaNone) {
        bitmapInfo = kCGImageAlphaNoneSkipLast;

    CGContextRef bitmap;

    if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
        bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    } else {
        bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);


    // In the right or left cases, we need to switch scaledWidth and scaledHeight,
    // and also the thumbnail point
    if (sourceImage.imageOrientation == UIImageOrientationLeft) {
        thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x);
        CGFloat oldScaledWidth = scaledWidth;
        scaledWidth = scaledHeight;
        scaledHeight = oldScaledWidth;

        CGContextRotateCTM (bitmap, M_PI_2); // + 90 degrees
        CGContextTranslateCTM (bitmap, 0, -targetHeight);

    } else if (sourceImage.imageOrientation == UIImageOrientationRight) {
        thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x);
        CGFloat oldScaledWidth = scaledWidth;
        scaledWidth = scaledHeight;
        scaledHeight = oldScaledWidth;

        CGContextRotateCTM (bitmap, -M_PI_2); // - 90 degrees
        CGContextTranslateCTM (bitmap, -targetWidth, 0);

    } else if (sourceImage.imageOrientation == UIImageOrientationUp) {
        // NOTHING
    } else if (sourceImage.imageOrientation == UIImageOrientationDown) {
        CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
        CGContextRotateCTM (bitmap, -M_PI); // - 180 degrees

    CGContextDrawImage(bitmap, CGRectMake(thumbnailPoint.x, thumbnailPoint.y, scaledWidth, scaledHeight), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage* newImage = [UIImage imageWithCGImage:ref];


    return newImage; 

The method we employ here is to create a bitmap with the desired size, but draw an image that is actually larger, thus maintaining the aspect ratio.

So We've Got Our Scaled Images - How Do I Save Them To Disk?

This is pretty simple. Remember that we want to save a compressed version to disk, and not the uncompressed pixels. Apple provides two functions that help us with this (documentation is here):

NSData* UIImagePNGRepresentation(UIImage *image);
NSData* UIImageJPEGRepresentation (UIImage *image, CGFloat compressionQuality);

And if you want to use them, you'd do something like:

UIImage* myThumbnail = ...; // Get some image
NSData* imageData = UIImagePNGRepresentation(myThumbnail);

Now we're ready to save it to disk, which is the final step (say into the documents directory):

// Give a name to the file
NSString* imageName = @"MyImage.png";

// Now, we have to find the documents directory so we can save it
// Note that you might want to save it elsewhere, like the cache directory,
// or something similar.
NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString* documentsDirectory = [paths objectAtIndex:0];

// Now we get the full path to the file
NSString* fullPathToFile = [documentsDirectory stringByAppendingPathComponent:imageName];

// and then we write it out
[imageData writeToFile:fullPathToFile atomically:NO];

You would repeat this for every version of the image you have.

How Do I Load These Images Back Into Memory?

Just look at the various UIImage initialization methods, such as +imageWithContentsOfFile: in the Apple documentation.

Answered By: Tetrad ( 25)

If you want to save the UIImage back into your user's photo roll there's a built in method for doing this as well.

UIImageWriteToSavedPhotosAlbum( UIImage* image, id target, SEL action, void* userdata);

Here's the signature of the saving finished callback (the action above):

- (void) image:(UIImage*)image didFinishSavingWithError:(NSError *)error contextInfo:(NSDictionary*)info;

You can, of course, omit the saving callback, but saving to the photo roll is non-atomic so you probably want some indicator.

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

I would like to check to see if I have an Internet connection on the iPhone using the Cocoa Touch libraries.

I came up with a way to do this using an NSURL. The way I did it seems a bit unreliable (because even Google could one day be down and relying on a 3rd party seems bad) and while I could check to see for a response from some other websites if Google didn't respond, it does seem wasteful and an unnecessary overhead on my application.

- (BOOL) connectedToInternet
    NSString *URLString = [NSString stringWithContentsOfURL:[NSURL URLWithString:@""]];
    return ( URLString != NULL ) ? YES : NO;

Is what I have done bad? (Not to mention stringWithContentsOfURL is deprecated in 3.0) And if so what is a better way to accomplish this?

Answered By: iWasRobbed ( 528)

Use a simple library to do it: (ARC and GCD Compatible Reachability)

OR... Do it yourself:

1) Add SystemConfiguration framework to the project but don't worry about including it anywhere

2) Add Reachability.h and Reachability.m to the project (you can get those here)

3) Add @class Reachability; to the .h file of where you are implementing the code

4) Create a couple instances to check in the interface section of the .h file:

Reachability* internetReachable;
Reachability* hostReachable;

5) Add a method in the .h for when the network status updates:

-(void) checkNetworkStatus:(NSNotification *)notice;

6) Add #import "Reachability.h" to the .m file where you are implementing the check

7) In the .m file of where you are implementing the check, you can place this in one of the first methods called (init or viewWillAppear or viewDidLoad etc):

-(void) viewWillAppear:(BOOL)animated
    // check for internet connection
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkNetworkStatus:) name:kReachabilityChangedNotification object:nil];

    internetReachable = [[Reachability reachabilityForInternetConnection] retain];
    [internetReachable startNotifier];

    // check if a pathway to a random host exists
    hostReachable = [[Reachability reachabilityWithHostName: @""] retain];
    [hostReachable startNotifier];

    // now patiently wait for the notification

8) Set up the method for when the notification gets sent and set whatever checks or call whatever methods you may have set up (in my case, I just set a BOOL)

-(void) checkNetworkStatus:(NSNotification *)notice
    // called after network status changes
    NetworkStatus internetStatus = [internetReachable currentReachabilityStatus];
    switch (internetStatus)
        case NotReachable:
            NSLog(@"The internet is down.");
            self.internetActive = NO;

        case ReachableViaWiFi:
            NSLog(@"The internet is working via WIFI.");
            self.internetActive = YES;

        case ReachableViaWWAN:
            NSLog(@"The internet is working via WWAN.");
            self.internetActive = YES;


    NetworkStatus hostStatus = [hostReachable currentReachabilityStatus];
    switch (hostStatus)
        case NotReachable:
            NSLog(@"A gateway to the host server is down.");
            self.hostActive = NO;

        case ReachableViaWiFi:
            NSLog(@"A gateway to the host server is working via WIFI.");
            self.hostActive = YES;

        case ReachableViaWWAN:
            NSLog(@"A gateway to the host server is working via WWAN.");
            self.hostActive = YES;


9) In your dealloc or viewWillDisappear or similar method, remove yourself as an observer

-(void) viewWillDisappear:(BOOL)animated
    [[NSNotificationCenter defaultCenter] removeObserver:self];

Note: There might be an instance using viewWillDisappear where you receive a memory warning and the observer never gets unregistered so you should account for that as well.

I know about the HIG (which is quite handy!), but what programming practices do you use when writing Objective-C, and more specifically when using Cocoa (or CocoaTouch).

Answered By: Kendall Helmstetter Gelner ( 400)

There are a few things I have started to do that I do not think are standard:

1) With the advent of properties, I no longer use "_" to prefix "private" class variables. After all, if a variable can be accessed by other classes shouldn't there be a property for it? I always disliked the "_" prefix for making code uglier, and now I can leave it out.

2) Speaking of private things, I prefer to place private method definitions within the .m file in a class extension like so:

#import "MyClass.h"

@interface MyClass ()
- (void) someMethod;
- (void) someOtherMethod;

@implementation MyClass

Why clutter up the .h file with things outsiders should not care about? The empty () works for private categories in the .m file, and issues compile warnings if you do not implement the methods declared.

3) I have taken to putting dealloc at the top of the .m file, just below the @synthesize directives. Shouldn't what you dealloc be at the top of the list of things you want to think about in a class? That is especially true in an environment like the iPhone.

3.5) In table cells, make every element (including the cell itself) opaque for performance. That means setting the appropriate background color in everything.

3.6) When using an NSURLConnection, as a rule you may well want to implement the delegate method:

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection
                  willCacheResponse:(NSCachedURLResponse *)cachedResponse
      return nil;

I find most web calls are very singular and it's more the exception than the rule you'll be wanting responses cached, especially for web service calls. Implementing the method as shown disables caching of responses.

Also of interest, are some good iPhone specific tips from Joseph Mattiello (received in an iPhone mailing list). There are more, but these were the most generally useful I thought (note that a few bits have now been slightly edited from the original to include details offered in responses):

4) Only use double precision if you have to, such as when working with CoreLocation. Make sure you end your constants in 'f' to make gcc store them as floats.

float val = someFloat * 2.2f;

This is mostly important when someFloat may actually be a double, you don't need the mixed-mode math, since you're losing precision in 'val' on storage. While floating-point numbers are supported in hardware on iPhones, it may still take more time to do double-precision arithmetic as opposed to single precision. References:

On the older phones supposedly calculations operate at the same speed but you can have more single precision components in registers than doubles, so for many calculations single precision will end up being faster.

5) Set your properties as nonatomic. They're atomic by default and upon synthesis, semaphore code will be created to prevent multi-threading problems. 99% of you probably don't need to worry about this and the code is much less bloated and more memory-efficient when set to nonatomic.

6) SQLite can be a very, very fast way to cache large data sets. A map application for instance can cache its tiles into SQLite files. The most expensive part is disk I/O. Avoid many small writes by sending BEGIN; and COMMIT; between large blocks. We use a 2 second timer for instance that resets on each new submit. When it expires, we send COMMIT; , which causes all your writes to go in one large chunk. SQLite stores transaction data to disk and doing this Begin/End wrapping avoids creation of many transaction files, grouping all of the transactions into one file.

Also, SQL will block your GUI if it's on your main thread. If you have a very long query, It's a good idea to store your queries as static objects, and run your SQL on a separate thread. Make sure to wrap anything that modifies the database for query strings in @synchronize() {} blocks. For short queries just leave things on the main thread for easier convenience.

More SQLite optimization tips are here, though the document appears out of date many of the points are probably still good;

Airsource Ltd

I would like to have an app include a custom font for rendering text, load it, and then use it with standard UIKit elements like UILabel. Is this possible?

I found these links:

but these would require me to render each glyph myself, which is a bit too much like hard work, especially for multi-line text.

I've also found posts that say straight out that it's not possible, but without justification, so I'm looking for a definitive answer.

EDIT - failed -[UIFont fontWithName:size:] experiment

I downloaded Harrowprint.tff (downloaded from here) and added it to my Resources directory and to the project. I then tried this code:

UIFont* font = [UIFont fontWithName:@"Harrowprint" size:20];

which resulted in an exception being thrown. Looking at the TTF file in Finder confirmed that the font name was Harrowprint.

EDIT - there have been a number of replies so far which tell me to read the documentation on X or Y. I've experimented extensively with all of these, and got nowhere. In one case, X turned out to be relevant only on OS X, not on iPhone. Consequently I am setting a bounty for this question, and I will award the bounty to the first person who provides an answer (using only documented APIs) who responds with sufficient information to get this working on the device. Working on the simulator too would be a bonus.

EDIT - it appears that the bounty auto-awards to the answer with the highest nunber of votes. Interesting. No one actually provided an answer that solved the question as asked - the solution that involves coding your own UILabel subclass doesn't support word-wrap, which is an essential feature for me - though I guess I could extend it to do so.

Answered By: commanda ( 167)

Edit: As of iOS 3.2, this functionality is built in. If you need to support pre-3.2, you can still use this solution.

I created a simple module that extends UILabel and handles loading .ttf files. I released it opensource under the Apache license and put it on github here: git://

The important files are FontLabel.h and FontLabel.m.

It uses some of the code from Genericrich's answer above.

Browse the source here:

Mickey Shine

I am a web developer and I want to move my web products to iPhone. One of the products is like Google Maps: show map on the phone screen, you can drag or resize the map and view some information that we add to the map.

I know there are some technologies that enables you to use HTML, CSS and Javascript to develop native iPhone apps. I've identified a few:

Are there other, similar products? What are the differences between them? Which should I choose?

Answered By: DennisJZH ( 370)

I registered with stackoverflow just for the purpose of commenting on the mostly voted answer on top. The bad thing is stackoverflow does not allow new members to post comments. So I have to make this comment more look like an answer.

Rory Blyth's answer contains some valid points about the two javascript mobile frameworks. However, his key points are incorrect. The truth is that Titanium and PhoneGap are more similar than different. They both expose mobile phone functions through a set of javascript APIs, and the application's logic (html, css, javascript) runs inside a native WebView control.

  1. PhoneGap is not just a native wrapper of a web app. Through the PhoneGap javascript APIs, the "web app" has access to the mobile phone functions such as Geolocation, Accelerometer Camera, Contacts, Database, File system, etc. Basically any function that the mobile phone SDK provides can be "bridged" to the javascript world. On the other hand, a normal web app that runs on the mobile web browser does not have access to most of these functions (security being the primary reason). Therefore, a PhoneGap app is more of a mobile app than a web app. You can certainly use PhoneGap to wrap a web app that does not use any PhoneGap APIs at all, but that is not what PhoneGap was created for.

  2. Titanium does NOT compile your html, css or javascript code into "native bits". They are packaged as resources to the executable bundle, much like an embedded image file. When the application runs, these resources are loaded into a UIWebView control and run there (as javascript, not native bits, of course). There is no such thing as a javascript-to-native-code (or to-objective-c) compiler. This is done the same way in PhoneGap as well. From architectural standpoint, these two frameworks are very similar.

Now, are they any different? Yes. First, Titanium appears to be more feature rich than PhoneGap by bridging more mobile phone functions to javascript. Most noticeably, PhoneGap does not expose many (if any) native UI components to javascript. Titanium, on the other hand, has a comprehensive UI APIs that can be called in javascript to create and control all kinds of native UI controls. Utilizaing these UI APIs, a Titanium app can look more "native" than a PhoneGap app. Second, PhoneGap supports more mobile phone platforms than Titanium does. PhoneGap APIs are more generic and can be used on different platforms such as iPhone, Android, Blackberry, Symbian, etc. Titanium is primarily targeting iPhone and Android at least for now. Some of its APIs are platform specific (like the iPhone UI APIs). The use of these APIs will reduce the cross-platform capability of your application.

So, if your concern for your app is to make it more "native" looking, Titanium is a better choice. If you want to be able to "port" your app to another platform more easily, PhoneGap will be better.

Updated 8/13/2010: Link to a Titanium employee's answer to Mickey's question.

Updated 12/04/2010: I decided to give this post an annual review to keep its information current. Many things have changes in a year that made some of the information in the initial post outdated.

The biggest change came from Titanium. Earlier this year, Appcelerator released Titanium 1.0, which departed drastically from its previous versions from the architectural standpoint. In 1.0, the UIWebView control is no longer in use. Instead, you call Titanium APIs for any UI functions. This change means a couple things:

  1. Your app UI becomes completely native. There is no more web UI in your app since the native Titanium APIs take over control of all your UI needs. Titanium deserves a lot of credit by pioneering on the "Cross-Platform Native UI" frontier. It gives programmers who prefer the look and feel of native UI but dislike the official programming language an alternative.

  2. You won't be able to use HTML or CSS in your app, as the web view is gone. (Note: you can still create web view in Titanium. But there are few Titanium features that you can take advantage of in the web view.)Titanium Q&A: What happened to HTML & CSS?

  3. You won't be able to use popular JS libraries such as JQuery that assume the existence of an DOM object. You continue to use JavaScript as your coding language. But that is pretty much the only web technology you can utilize if you come to Titanium 1.0 as a web programmer.

Titanium video: What is new in Titanium 1.0.

Now, does Titanium 1.0 compile your JavaScript into "native bits"? No. Appcelerator finally came clean on this issue with this developer blog:Titanium Guides Project: JS Environment. We programmers are more genuine people than those in the Marketing department, aren't we? :-)

Move on to PhoneGap. There are not many new things to say about PhoneGap. My perception is that PhoneGap development was not very active until IBM jumped on board later this year. Some people even argued that IBM is contributing more code to PhoneGap than Nitobi is. That being true or not, it is good to know that PhoneGap is being active developed.

PhoneGap continues to base itself on web technologies, namely HTML, CSS and JavaScript. It does not look like PhoneGap has any plan to bridge native UI features to JavaScript as Titanium is doing. While Web UI still lags behind native UI on performance and native look and feel, such gap is being rapidly closed. There are two trends in web technologies that ensure bright feature to mobile web UI in terms of performance:

  1. JavaScript engine moving from an interpreter to a virtual machine. JavaScript is JIT compiled into native code for faster execution. Safari JS engine: SquirrelFish Extreme

  2. Web page rendering moving from relying on CPU to using GPU acceleration. Graphic intensive tasks such as page transition and 3D animation become a lot smoother with the help of hardware acceleration. GPU Accelerated Compositing in Chrome

Such improvements that are originated from desktop browsers are being delivered to mobile browsers quickly. In fact, since iOS 3.2 and Android 2.0, the mobile web view control has become much more performing and HTML5 friendly. The future of mobile web is so promising that it has attracted a big kid to town: JQuery has recently announced its mobile web framework. With JQuery Mobile providing UI gadgets, and PhoneGap providing phone features, they two combined creates a perfect mobile web platform in my opinion.

I should also mention Sencha Touch as another mobile web UI gadget framework. Sencha Touch version 1.0 was recently released under a dual licensing model that includes GPLv3. Sencha Touch works well with PhoneGap just as JQuery Mobile does.

If you are a GWT programmer(like me), you may want to check out GWT Mobile, an open source project for creating mobile web apps with GWT. It includes a PhoneGap GWT wrapper that enables the use of PhoneGap in GWT.


I was testing my app on the simulator when it crashed on clicking a button of a UIAlertView. I stopped debugging there, made some changes to the code and built the app again. Now when I run the application, I get this error in the console

Couldn't register com.myApp.debug with the bootstrap server. Error: unknown error code. This generally means that another instance of this process was already running or is hung in the debugger.Program received signal: “SIGABRT”.

I tried removing the app from the simulator, doing a clean build but I still get this error when I try to run the app.

What should I do to be able to run the app on my simulator again?

Answered By: Elliot Kroo ( 135)

Try quitting and restarting the simulator? If "worse comes to worst" you can always try restarting: in my experience this should fix it.


How much can a developer charge for an iPhone app like Twitterrific?

I want to know this because I need such an application with the same functionality for a new community website. I can do Ruby but have no experience with Objective-C. So it would be interesting for me if I should start reading books about iPhone programming or outsource the work to a iPhone programmer.

Answered By: chockenberry ( 1010)

I'm one of the developers for Twitterrific and to be honest, I can't tell you how many hours have gone into the product. I can tell you everyone who upvoted the estimate of 160 hours for development and 40 hours for design is fricken' high. (I'd use another phrase, but this is my first post on Stack Overflow, so I'm being good.)

Twitterrific has had 4 major releases beginning with the iOS 1.0 (Jailbreak.) That's a lot of code, much of which is in the bit bucket (we refactor a lot with each major release.)

One thing that would be interesting to look at is the amount of time that we had to work on the iPad version. Apple set a product release date that gave us 60 days to do the development. (That was later extended by a week.)

We started the iPad development from scratch, but a lot of our underlying code (mostly models) was re-used. The development was done by two experienced iOS developers. One of them has even written a book: :-)

With such a short schedule, we worked some pretty long hours. Let's be conservative and say it's 10 hours per day for 6 days a week. That 60 hours for 9 weeks gives us 540 hours. With two developers, that's pretty close to 1,100 hours. Our rate for clients is $150 per hour giving $165,000 just for new code. Remember also that we were reusing a bunch existing code: I'm going to lowball the value of that code at $35,000 giving a total development cost of $200,000.

Anyone who's done serious iPhone development can tell you there's a lot of design work involved with any project. We had two designers working on that aspect of the product. They worked their asses off dealing with completely new interaction mechanics. Don't forget they didn't have any hardware to touch, either (LOTS of printouts!) Combined they spent at least 25 hours per week on the project. So 225 hours at $150/hr is about $34,000.

There are also other costs that many developer neglect to take into account: project management, testing, equipment. Again, if we lowball that figure at $16,000 we're at $250,000. This number falls in line with Jonathan Wight's (@schwa) $50-150K estimate with the 22 day Obama app.

Take another hit, dude.

Now if you want to build backend services for your app, that number's going to go up even more. Everyone seems surprised that Instagram chewed through $500K in venture funding to build a new frontend and backend. I'm not.


Tried to rebuild an app that was just working yesterday. Got a message that a profile had expired, so I removed it from the iPod and from Itunes. When I chose a new profile (one with an * in the identifier), I now get an error:

Code Sign Error: Provisioning Profile (long string) can't be found.

What am I missing? I looked through related questions and didn't see this scenario already. Thanks

Answered By: Brad Smith ( 564)

Sometimes your xcode project file gets messed up, especially if you have an old project and first created it with an older version of xcode/iphone sdk. What you need to do is open up the project file in a text editor, search for the 'long string' from your error and manually erase that line. In fact, you should just go ahead and erase any line that points to any provisioning profiles. Then reopen the project in xcode, go to the settings and reselect your new profile. This clears up issues like that most of the time. The lines that point to the provisioning profiles will look like this:

"PROVISIONING_PROFILE[sdk=iphoneos*]" = "487F3EAC-05FB-4A2A-9EA0-31F1F35760EB";