Explanation of method headers in objective-c (for beginners)

This is a short explanation for beginners coming from other languages like Java or PHP to show how classes are instantiated and how methods are called and defined.

To define a method in programming languages you usually have 3-4 Parts:

1.) Keyword to say that you are about to implement a method (e.g. function)
2.) What kind of object will the method return or void if nothing
3.) The method name
4.) Parameters

Lets say we have a class called calculator.
In this class we want to implement a method called increment. This method gets an integer and returns the integer incremented by one.
This method would look in php like this:

function increment($prmInt){
   return $prmInt++;
}

In objective-c the same method would look like this:

-(int)increment:(int)intSomeNumber{
   return intSomeNumber++;
}

"-"   is equal to the word "function" and tells the compiler that a method starts
"(int)"   defines what will be send back by the method (void if nothing)
"increment"   this is the method name
":"   tells the compiler that a parameter starts
"(int)intSomeNumber"   type and name of parameter

If you want to create a method with several parameters you can just add ":" and some text at the end.
Some examples:

-(void)doSomething:(NSString*)strParameter1 andEvenMoreParameters:(NSString*)strParameter2;
-(void)aMethodWithoutTextbetweeenParameters:(int)i1:(int)i2:(int)i3;

To call these methods you have to instantiate the class:

Calculator* calc =  [[Calculator alloc] init];

now you have allocated an object. With this object you can call the declared method:


int intNumber = 5;
intNumber = [calc increment:intNumber];

and for completeness' sake:

[calc doSomething:@"string1" andEvenMoreParameters:@"string2"];
[calc aMethodWithoutTextbetweeenParameters:1:2:3];

As we don't need the object anymore we will release it so that the memory gets freed:

[calc release];

Cheers

JayEs

Asynchronous download/request with Objective-C

For handling asynchronous request there is a very neat and simple mechanism in Objective-C.

Delegates

The following header file defines a protocol for the delegate and the necessary methods and data types to create a downloader that constantly pushes an update about the download state to the main thread.

Header File

@protocol DownloaderDelegate; #import <Foundation/Foundation.h> @interface Downloader : NSObject { id <DownloaderDelegate> delegate; NSString* strFileNameWithPath; NSURLConnection* connection; CGFloat floatTotalData; CGFloat floatReceivedData; } @property(nonatomic, retain) NSString* strFileNameWithPath; @property(nonatomic, retain) id <DownloaderDelegate> delegate; -(void)loadData; -(float)getProgressInPercent; @end @protocol DownloaderDelegate <NSObject> @optional -(void)didReceiveData:(Downloader *)d; //will be called each time data has been received -(void)didLoadData:(Downloader *)d; //will be called when the download has finished @end

Implementation

#import "Downloader.h" @implementation Downloader @synthesize strFileNameWithPath; @synthesize delegate; -(void)loadData{ floatTotalData = 100; floatReceivedData = 0; self.strFileNameWithPath = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"tmp"]; self.strFileNameWithPath = [self.strFileNameWithPath stringByAppendingPathComponent:@"someFile.zip"]; [[NSFileManager defaultManager] createFileAtPath:self.strFileNameWithPath contents:nil attributes:nil]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://url.com/getData.php"]]; //this block shall show how to add POST variables to the request NSString *encodedParameterPairs = [NSString stringWithFormat:@"uid=%@", [[UIDevice currentDevice] uniqueIdentifier]]; NSData *requestData = [encodedParameterPairs dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES]; [request setHTTPMethod: @"POST"]; [request setHTTPBody:requestData]; [NSURLConnection connectionWithRequest:request delegate:self]; //request is send here } - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { //store how big file is going to be floatTotalData = [[NSString stringWithFormat:@"%lli",[response expectedContentLength]] floatValue]; } - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { floatReceivedData += [data length]; //add new data to the end of the file NSFileHandle *fileHandle = [NSFileHandle fileHandleForUpdatingAtPath: self.strFileNameWithPath]; [fileHandle seekToEndOfFile]; [fileHandle writeData: data]; [fileHandle closeFile]; //if delegate did implement the method didReceiveData let him know about the new data if ([self.delegate respondsToSelector:@selector(didReceiveData:)]) [self.delegate didReceiveData:self]; } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { //do something with the received data.... //and let the delegate know that the download has finished if ([self.delegate respondsToSelector:@selector(didLoadData:)]) [self.delegate didLoadData:self]; } -(float)getProgressInPercent{ //if you want to show a progressbar or something similar call this method in //the delegate method didReceiveData return (floatReceivedData / floatTotalData) * 100.0f; } - (void)dealloc { //free memory [strFileNameWithPath release], strFileNameWithPath = nil; delegate = nil; [super dealloc]; } @end

This implementation is ment for big files like 200 MB zip files. If you just want to download small stuff like an image u can instead of writing into a file use a NSData object.

Hope this tutorial did help. Feel free to post some code improvements or questions in the comments?

P.S.: Will look for a nicer way to post code in blogger. For the moment I don't have a lot of time (child n.3 was born two days ago... ;o) ) so ill leave it this way.


Cheers,

JayEs

Here the code as Pastie-link:

header-file
implementation

google latitude in app store

Even this blogs main purpose is to write about development here and there ill post apps,technologies and tools i find especially usefull or cool....

Google latitude hit the app store this week and I must say its great. It took some time to come over from Android but it finally made it. I already felt in love with it on my old HTC Magic and am really happy about the look and feel on iOS.

Hope to see many more Google Apps on iOS Devices (even though they have there own OS) in the future...

JSON in iPhone/iPad App

For you out there searching for a good JSON library for your iOS project this is the one Im using:


https://github.com/stig/json-framework/downloads

Howto use:

1. Add folder to your project
2. Import the header file (#import "JSON.h")
3. When you have a NSString containing JSON data simply use: [strSomeString JSONValue]; and you get an NSDictionary/NSArray

Very simple :-)


Cheers,

JayEs

For/Foreach -> php vs objective-c

Lets start with a short Post about for/foreach PHP vs Objective-C
 To loop through an array in php is very simple:

foreach($arrData as $key => $value){
    //do something...
}

or

for($i = 0; $i < count($arrData); $i++){
    //do somethin... 
}

In Objective-C you have similar possibilities but you have to be sure what kind of object you are dealing with e.g. NSDictionary* or NSArray*

To get an Element of these two types you do as follows:

NSDictionary

NSDictionary* arrData = ...;
 [arrData objectForKey:@"id"];

Loop

for (NSString* key in arrData) {
        id value = [arrData objectForKey:key];
}

NSArray


NSArray* arrData = ...;
 [arrData objectAtIndex:1];

Loop

for (int i = 0; i < [arrData count]; i++) {
     [arrData objectAtIndex:i];
}

Besides these options you can also use enumerateKeysAndObjectsWithOptions. But I personaly dislike it cause it "feels" bad.

If you have an array of similar objects and you want all of them to perform the same selector you can also do this:

[[self.view subviews] makeObjectsPerformSelector:@selector(removeFromSuperview)];

This will save you some lines of code and is very "readable".

Cheers

JayEs

First Post

This is going to be a blog about dev and tech related topics.
The main topics regarding development will be:

• Objective-C / Cocoa
• PHP
• Java / Android

 Like many developers when faceing a specific problem I often start googling for it to see how other people solved it. This Blog shall show code blogs I found usefull or highlight specific topics the community asks for. To help others out there trying to solve a task...