// From NSString to NSData
NSString *text = @"Some string";
NSData *data = [text dataUsingEncoding:NSUTF8StringEncoding];
 
// From NSData to NSString
NSString *text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

Who knows if it helps some one else.

Here’s a way to keep your UITableViewController (or any other view controller or class your using as datasource or delegate) clean, this approach is aimed at tables with multiple sections. Tables with 1 section have limited benefit of using this approach although extra sections could be easily added later. The key is to move all the logic for a specific section in a table to its own class, which is responsible for his own rows and nothing more.

To achieve this we create a protocol called YCSectionController:

@protocol YCSectionController
 
@required
 
- (NSInteger)tableView:(UITableView *)table numberOfRowsInSection:(NSInteger)section;
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath;
 
@optional
 
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath;
 
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section;
- (NSString *)tableView:(UITableView *)tableView titleForFooterInSection:(NSInteger)section;
 
@end

This protocol will be used to specify to which methods a custom section controller must conform. Each custom section controller has knowledge about the amount of rows & how to display each row, these are the required methods. Extra methods can be added like what to do when a row is selected for instance. Depending on the appearance of the section & the desired behavior each custom section controller class implements the necessary methods.

The YCHeaderSectionController implementation below shows a minimal implementation.

@implementation YCHeaderSectionController
 
#pragma mark YCSectionController methods
 
- (NSInteger)tableView:(UITableView *)table numberOfRowsInSection:(NSInteger)section {
	return 1;
}
 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
	NSString *cellIdentifier = @"HeaderCell";
 
	UITableViewCell *cell = (UITableViewCell*)[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (cell == nil) {
		cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];
		cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
	}
 
	if (indexPath.row == 0) {
		cell.textLabel.text = @"Yannick Compernol";
 
	}
 
	return cell;
}
 
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
	NSURL *url = nil;
 
	if (indexPath.row == 0) {
		url = [NSURL URLWithString:@"http://yannick.compernol.be"];
	}
 
	if (url) {
		[[UIApplication sharedApplication] openURL:url];
	}
}
 
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
	return @"Info";
}
 
@end

One you’ve made several custom section controllers all you have to is to hook them up in your UITableViewController and dispatch the datasource/delegate methods to the custom section controllers. Note the UITableViewControllers has an array which will hold all the custom section controllers, the array is filled in the ViewDidLoad: method.

@interface MainTableViewController : UITableViewController {
	NSArray *sectionControllers;
}
@end
 
@implementation MainTableViewController
 
...
 
#pragma mark UIViewController methods
 
- (void)viewDidLoad {
    [super viewDidLoad];
 
	id header = [[YCHeaderSectionController alloc] init];
	id content = [[YCContentSectionController alloc] init];
	id footer = [[YCFooterSectionController alloc] init];
 
	sectionControllers = [[NSArray alloc] initWithObjects:header, content, footer, nil];
 
	[header release];
	[content release];
	[footer release];
}
 
...
 
#pragma mark UITableViewDataSource methods
 
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
	return [sectionControllers count];
}
 
- (NSInteger)tableView:(UITableView *)table numberOfRowsInSection:(NSInteger)section {
	id<YCSectionController> sectionController = [sectionControllers objectAtIndex:section];
	return [sectionController tableView:table numberOfRowsInSection:section];
}
 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
	id<YCSectionController> sectionController = [sectionControllers objectAtIndex:indexPath.section];
	return [sectionController tableView:tableView cellForRowAtIndexPath:indexPath];
}
 
...
 
#pragma mark UITableViewDelegate methods
 
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
	id<YCSectionController> sectionController = [sectionControllers objectAtIndex:indexPath.section];
	if ([sectionController respondsToSelector:@selector(tableView:didSelectRowAtIndexPath:)]) {
		[sectionController tableView:tableView didSelectRowAtIndexPath:indexPath];
	}	
}
 
@end

And that is about it, it can be taken further than I showed here, but I think this is a decent starter. The bottom line is that the UITableViewController has less code and the specific code (appearance & behavior) for each section is contained in its own class. Adding to the maintainability of the whole table.

A running example (screenshot shown above) can be downloaded here.

There’s only one thing I’m still struggling with, since id does not have a respondsToSelector: method, you’ll get a warning that respondsToSelector: wasn’t found in the protocol. An easy fix would be to add it to the protocol, but that doesn’t feel right as it’s not part of the behavior I wanted to encapsulate in the section controller. I’d love to hear your thoughts/comments on this!

Apple definitely made it easier with new SDK, since we can interact directly with the UILabel. I know it’s pretty straightforward, but I’m always surprised by how many developers disregard the documentation & turn to forums/blogs for help.

Creating multiline cells is now as simple as setting the numberOfLines property to 0 (or a predefined number) of the textLabel, which is in turn a property of the cell. Given the height of the cell is sufficient, behold a multiline cell.

cell.textLabel.text = @"Some long text...";
cell.textLabel.numberOfLines = 0;

Change the height of the cell with the tableView:heightForRowAtIndexPath: delegate method of the UITableViewController, either by returning a fixed height or by calculating the height needed to show the desired text.

Note that the text property of a cell is being deprecated in favor of textLabel.text, more info on the new 3.0 predefined cell styles can be found here.

Instead of looping through the contents of the nib, the key are IBOutlets. Create a NSView IBOutlet in your controller class were you’ll want to use the view. Next step is to open your nib file which contains your external view and change the File Owner’s class identity to the controller class you’ve just extended with the IBOutlet for the view. Now just ctrl-drag from the File Owner to your view and select your desired IBOutlet from the list.

Now you’ve connected your controller and the external view, yet the IBOutlet will not be hooked up automatically when your controller’s created. This is a good thing because we can postpone loading the extra nib to when it’s really necessary saving resources for other, more important stuff. This is a practice Apple encourages, using multiple nib files and loading them dynamically when needed.

This is the code needed to load the nib, it’ll automaticall hook up your controller’s IBOutlet to your view.

[[NSBundle mainBundle] loadNibNamed:@"YourNibName" owner:self options:nil];

Simple? Indeed, yet it took me a while to realize using an external nib is basically just the same as putting all your views in a single nib container. It’s all based on hooking up IBOutlets.

First we’ll create the actual loading view, let’s add an empty XIB to our Xcode project called LoadingView. Add a UIView to the nib and drag a UIImageView onto it. Use a vector program like Inkscape to create a black rectangle with rounded corners. Use a UILabel and a UIActivityIndicator to create something like the screenshot to the right. Be sure to check the animating property of the activity indicator and change the alpha of the root view to 0.8 for intance, since we want the view to be slightly transparant.

Once we’ve made the actual view, it’s time to show it.

- (UIView*)newLoadingView {
   NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"LoadingView" owner:self options:nil];
 
   NSEnumerator *enumerator = [nib objectEnumerator];
   id object;
 
   while ((object = [enumerator nextObject])) {
      if ([object isMemberOfClass:[UIView class]]) {
         return object;
      }
   }
 
   return nil;
}
 
- (void)doWork {
   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 
   // Add lenghty operation.
 
   [loadingView removeFromSuperview];
   [pool release];
}
 
- (void)someMethod {
   loadingView = [self newLoadingView];
   loadingView.center = CGPointMake(160, 350);
   [self.view addSubview:loadingView];
 
   [NSThread detachNewThreadSelector:@selector(doWork) toTarget:self withObject:nil ];
}

We’re using the newLoadingView: method to retrieve the view from the nib, the reason we’re looping through the contents of the nib is one cannot garantee the order in which items are retrieved will always be the same. For instance the index of the loading view will be different in firmware version 2.0 and 2.1. We retrieve a UIView item, in this case the loading view, since it’s the only UIView in the nib. I’m sure this code could be improved though, using your own derived UIView and checking for this derived class would be better. The center property of the loading view can be used to position the view, the top left corner has coordinates 0,0. (If anyone has a better method of getting a specific view from a nib, do tell)

The someMethod method is the one to call to start everything, this method will show the actual loading view and start the doWork method on a seperate thread. The reason we’re using a seperate thread is not to lock up the interface, otherwise the interface would freeze while the lenghty operation would be performed. The doWork method hides the loading view once everything is done.

Extension: The above code has one disadvantage, when using a tab controller the loading view will disappear once another tab is selected, returning to the original tab will show the loading view again though. In some cases this behaviour isn’t wanted, how do we solve this? Instead of showing the loading view on top of the content view displayed by the tab controller, we’ll show it on top of all the views, on top of the tab controller.

// Show loading view on top of everything
[[UIApplication sharedApplication].keyWindow addSubview:loadingView];

And that’s all there is to it.

Update: here’s the correct method to load a view from a separate nib file.

There you have it.

The basic idea is to use a dictionary which stores the received data per tag, remember that the actual connection cannot be used as the key of a dictionary. Each NSURLConnection methods retrieve the NSMutableData object from the dictionary based on the tag and does it magic with it.

If you don’t know how to use the NSURLConnection class, take a look at the documentation. That should get you going in no time.

First of all add a mutable dictionary to the header file:

NSMutableDictionary *receivedData;

Here’s the actual code. The load method starts the actual asynchronous calls. The startAsyncLoad:tag and dataForConnection methods are convenience methods to keep the code tidy & readable.

- (void)startAsyncLoad:(NSURL*)url tag:(NSString*)tag {
   NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
   CustomURLConnection *connection = [[CustomURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES tag:tag];
 
   if (connection) {
      [receivedData setObject:[[NSMutableData data] retain] forKey:connection.tag];
   }
}
 
- (NSMutableData*)dataForConnection:(CustomURLConnection*)connection {
   NSMutableData *data = [receivedData objectForKey:connection.tag];
   return data;
}
 
- (void)load {
   receivedData = [[NSMutableDictionary alloc] init];
 
   NSURL *url1 = [NSURL URLWithString:@"http://blog.emmerinc.be"];
   NSURL *url2 = [NSURL URLWithString:@"http://www.emmerinc.be"];
   NSURL *url3 = [NSURL URLWithString:@"http://twitter.com/emmerinc"]; 
 
   [self startAsyncLoad:url1 tag:@"tag1"];
   [self startAsyncLoad:url2 tag:@"tag2"];
   [self startAsyncLoad:url3 tag:@"tag3"];
}
 
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
   NSMutableData *dataForConnection = [self dataForConnection:(CustomURLConnection*)connection];
   [dataForConnection setLength:0];
}
 
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
   NSMutableData *dataForConnection = [self dataForConnection:(CustomURLConnection*)connection];
   [dataForConnection appendData:data];
}
 
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
   NSMutableData *dataForConnection = [self dataForConnection:(CustomURLConnection*)connection];
   [connection release];
 
   // Do something with the dataForConnection.
}

In the connectionDidFinishLoading: method the tag of the connection should be used to determine what to do with the actual received data. And that is about it!

Don’t forget to release the dictionary in the deconstructor or after all the asynchronous calls have been completed though.

Blog: Cocoa with Love
Includes an asteriods style game in CoreAnimation how to.

Blog: CrystalMinds
Includes a Duck Hunt game with regular UIViews how to.

Documentation: Create a singleton instance
Apple documentation on how to create a singleton instance.

Code snippets: iPhone SDK Examples
Some simple but useful examples.

Blog: iPhone Development
Decent blog with some good articles.

Forum: iPhone Dev SDK
One of the largest forums regarding iPhone (and Mac) development, contains an interesting business sub-forum.

Blog: iPhone Developer Tips
Another active and useful blog.

Blog: iPhone Development Bits
Has some nice links to other articles including a little game.

That’ll be it for now.

Since using multiple asynchronous connections implies handling the received data chunks yourself, one is likely to create a dictionary which contains a NSMutableData object for each NSURLConnection key. Unfortunately does a NSDictionary copy its keys and this is not something a NSURLConnection supports. A quick solution to avoid this is to make a subclass with a tag to distinguish each connection. This tag can be used as key in the dictionary.

Interface:

@interface CustomURLConnection : NSURLConnection {
   NSString *tag;
}
 
@property (nonatomic, retain) NSString *tag;
 
- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately tag:(NSString*)tag;
 
@end

Implementation:

@implementation CustomURLConnection
 
@synthesize tag;
 
- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately tag:(NSString*)tag {
   self = [super initWithRequest:request delegate:delegate startImmediately:startImmediately];
 
   if (self) {
      self.tag = tag;
   }
   return self;
}
 
- (void)dealloc {
   [tag release];
   [super dealloc];
}
 
@end

As you can see, creating a subclass with a tag property is rather easy and solves the dictionary issue.

To solve this difference in format, one could manipulate the actual string to comply to the desired format or one could use the NSDateFormatter class. The latter being the “cleanest” solution.

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];
NSDate *date = [formatter dateFromString:text];

The used format patterns comply to the Unicode standard UTS #35.