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CSCW Lab- iPhone
iMeet application presentation
Jul 25th
Finally, the biggest moment: application is ready!! I am very proud of this application, as it represents my achievements in fast learning and adapting to:
- new way of programming, as XCode and Interface Builder truly represent the ModelViewController paradigm
- new language- Objective-C, which as any language has its pluses and minuses
- new device: mobile devices on which I didn’t work since my experience on Sales Force Automation in TotalSoft company, back in 2005, on Windows CE.
I’ve structured the application visually in few areas:
1. Login screen – the ‘”gate” to the application. Since the access to the
XML-RPC is done in a secure way, the application implemented also a credential input and recording mechanism. The mechanism is dual: user can enter the login into the first screen or in the iPhone Settings application. Depends only on him where and how he’ll manage his credentials.
The main point of this screen is to create a intuitive interface for users to insert their credentials, instead of having to leave the application and go to the iPhone settings.
Objective-C: Putting markers on Map control
Jul 21st
This article comes as a completion to my previous ones, XCode : using MapKit with no geocoding available out of the box and XCode: Modal windows – Google maps and shows how to add pins on your already created Map View.
First of all, adding the points to the map is not as intuitive as it might seem, so let’s start by creating a new class called POI – point of interest. Its header must be filled with this code:
#import <foundation foundation.h> #import <mapkit mapkit.h> #import <corelocation corelocation.h> @interface POI : NSObject{ CLLocationCoordinate2D coordinate; NSString *subtitle; NSString *title; } @property (nonatomic, readonly) CLLocationCoordinate2D coordinate;@property (nonatomic,retain) NSString *subtitle;@property (nonatomic,retain) NSString *title;- (id) initWithCoords:(CLLocationCoordinate2D) coords; @end
XCode : using MapKit with no geocoding available out of the box
Jul 15th
One of the tasks in the CSCW lab was to create a map on which the users to see the location of a specific address.
So I started working on it, knowing that the newest framework brings a lot of goodies, through which there is also a map framework. But surprise! Apple provides only reverse geocoding, not forward geocoding. This means that you can only transform a pair of Latitude / Longitude to the Map and it will show it to the user. But what to do when user enters an address?
My point is that nobody caries with him a GPS to search for the address, get the coordinates and enter them into my map!
I was curious about it and after a little search I found that there was a big argue about the geocoding and Apple didn’t want to pay the price that Google and Tom-Tom asked for this feature.
Objective-C: Base64 to NSString and NSString to Base64
Jul 11th
While working on the CSCW Lab project, I encountered a situation in which the XML-RPC call returned an image, of course encoded as Base64. And guess what – in its known style, Apple doesn’t provide Base64 encoding and decoding – quite lame, given the fact that this encoding is used everywhere in data transfer over the internet – e-mail, browsers, web services – all of them use at some point this encoding to overcome the different local encodings on each one’s machine.
Once identified this problem, I had to solve it somehow – but guess what? – over the free sources there aren’t too many functions that provide this simple and basic encoding.
Finally, after few hours of searching, I finally found that Eric Czarny had a very successful implementation of this in its Cocoa XML-RPC Framework . After taking a quick look at its code, I end up using and importing into my project the
- NSStringAdditions.h. NSStringAdditions.m – providing the new category
+ (NSString *)base64StringFromData: (NSData *)data length: (int)length;
- NSDataAdditions.h and NSDataAdditions providing the new category:
+ (NSData *)base64DataFromString: (NSString *)string;
Being categories, they are automatically added to NSString and NSData automatically at runtime, thus their usage is straight forward :
UIImageView *uiIV;
// currentElementValue holds the string representation of the image, encoded in Base64
NSData *nsD = [NSData base64DataFromString: [dataLayer currentElementValue]];
if ([nsD ){
uiIV = [[UIImageView alloc] initWithImage:[UIImage imageWithData: nsD]];
}
Processing NSDate into an ISO8601 string
Jul 6th
During the CSCW Lab, where I had the experience of working on iPhone, I had to connect to a XML RPC server. Some of the parameters of the request had to be formatted as ISO8601 standard. After some reading, I end up using the following code, managing both the conversion of a NSDate to NSString and a NSString to a NSDATE using the above format:
NSString –> NSDate
-(NSString *) strFromISO8601:(NSDate *) date {
static NSDateFormatter* sISO8601 = nil;
if (!sISO8601) {
sISO8601 = [[NSDateFormatter alloc] init];
NSTimeZone *timeZone = [NSTimeZone localTimeZone];
int offset = [timeZone secondsFromGMT];
NSMutableString *strFormat = [NSMutableString stringWithString:@"yyyyMMdd'T'HH:mm:ss"];
offset /= 60; //bring down to minutes
if (offset == 0)
[strFormat appendString:ISO_TIMEZONE_UTC_FORMAT];
else
[strFormat appendFormat:ISO_TIMEZONE_OFFSET_FORMAT, offset / 60, offset % 60];
[sISO8601 setTimeStyle:NSDateFormatterFullStyle];
[sISO8601 setDateFormat:strFormat];
}
return[sISO8601 stringFromDate:date];
}
Objective-C: Use NSXMLParser
Jul 3rd
Almost any time you’ll need to pull some data from the web. Using Objective-C you have at your disposal a pretty good XML parser – the event-based version. What really means is that instead of building in-memory tree with the structure of the XML you’ll have some events raised when the parser encounters a special token – the most usual ones are tag start, tag end and found comments. The parsing goes node by node and is not nesting-sensitive. As soon as the parser returns you a node, you don’t know where in the structure you are currently anymore. As long as you have a clearly defined structure where each element is always present, you could do this using a counter. However, as soon as you have multiple nodes with no defined count, you have a problem.
The usage is simple and straight-forward. For simplicity, we assume that we have only have one level of children under the root node, but this can be easily extended to many levels. We’ll see some code and after that the detailed explanations:
- (void)parseJourneyData:(NSData *)data parseError:(NSError **)err {
// create and allocate the parser - it must be initiated with the XML data that we received or loaded
NSXMLParser *xmlParser= [[NSXMLParser alloc] initWithData:data];
self.arrResult= [[NSMutableArray alloc] init];
// Create the array for holding the resulted data
[xmlParser setDelegate:self];
// The parser calls will be redirected to methods in this class
[xmlParser setShouldProcessNamespaces:NO];
// We are not interested in namespaces
[xmlParser setShouldReportNamespacePrefixes:NO];
// neither in prefixes
[xmlParser setShouldResolveExternalEntities:NO];
// just data, no other stuff
[xmlParserparse];
// Parse that data.. here the parsing begins and the delegated methods will get called
//the parsing process ended and we check for errors
if (err && [xmlParser parserError]) {
*err = [xmlParser parserError];
}
[xmlParser release];
//cleaning the remainders
}
Objective-C: NSDictionary and NSMutableDictionary can’t keep the order of entries
Jun 30th
My latest task in CSCW Lab was to create the parser class for parsing some huge and multilevel XML. All nice and easy at first sight. Since the XML was the result of an RPC call, I got back some structures corresponding to NSDictionary and some arrays corresponding to NSArray in Apple’s Objective-C.
While iterating in the structure using NSXMLParser, a event-based parser, I kept adding the pairs as name and values to the parent.The normal approach would be to add the name and NSNull for value first, then when retrieving the value’s content, search the last inserted entry ( the pair composed by name and value) and just fill the value with content. First I instantiate the strKey with the last key obtained from the array who contains all dictionary keys, then I set the value for the key already computed.The code that I used was :
// get the last element in the dictionary and set it's value NSString *strKey = [[(NSMutableDictionary *)parentObj allKeys] lastObject]; [(NSMutableDictionary *)parentObj setObject:theValue forKey:strKey];
But surprise! the last value is the same always (in my specific case the first added element). What the heck ? 
Digging more deeply into this, seems that setObject:ForKey doesn’t ADD at the end of the dictionary, but more randomly insert the elements.
Objective-C: UIAlert or asking for confirmation
Jun 29th
While start XCoding, I faced a new challenge : how to create modal, single use confirmation dialogs? So after some digging in the internet, I found out that this can be actually done pretty simple and elegant. This will be very useful if you want to display some deletion confirmation or ask for user permission to use the camera or GPS sensor. All you have to do is just create a UIAlert and the IBAction hooked up to your “Nuclear launch” button, and then have its delegate decide whether to destroy the world or not.
In the header file you have to add this declaration of the action performed when the fatal button is clicked:
- (IBAction) btnLaunchNuclearStrikeClicked:(id)sender - (IBAction) deleteButtonClicked:(id)sender; Read the rest of this entry »
UIImageView setImage problem
Jun 28th
While working for this semester’s CSCW lab project, I encountered a strange situation: no matter what I did, the UIImageView didn’t load the image. After some digging on the Internet about this, I found out that first thing to look for is whether you’re sending the setImage message to the UIImageView instance you expect.
Being newbie in XCode and Apple’s technologies in general, I forgot to use NSLog. So my advice is to check and check often with NSLog for a nil pointer in the same place you’re trying to set the image. Obj-C loves to make freshman crazy by sending messages to nil pointers without any warning or other problem. So check if the pointer is nil, double check the IBOutlet connection to the UIImageView in IB.
Xcode – String concatenation
Jun 6th
Don’t be fooled that Objective-C is a Object oriented language. For decades operators overloading is something standard in almost all of them.
But in Objective-C you don’t have it. Mostly, I believe that comes from the struggle of Apple guys to assure the stability of the system. A lot of errors can come from poorly designed overloads, thus the crashes can appear.
Now let’s put some hands on code.
In C, Java or Pascal you would have written something like the following for string concatenation:
string1 = string2 + string3;
But in Objective-C you need to do something different:
NSString *myString = @"http://www.mywebsite.com"; float myValue = 4; NSString *result = [NSString stringWithFormat:@"%@?query=%.3f&a",myString,myValue]; myLabel.text=result;
But beware! Read the documentation regarding formats!
It is very important to use the correct String Format Specifiers:
- %S is used for a "Null-terminated array of 16-bit Unicode characters". And %s is used for a "Null-terminated array of 8-bit unsigned characters.
- %s interprets its input in the system encoding rather than, for example, UTF-8.". The key being that these are arrays, not objects.
- %@: "Objective-C object, printed as the string returned by descriptionWithLocale: if available, or description otherwise". That sounds a bit more like a NSString. It’s an Objective-C object after all.
