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

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

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...