Tech Talk by Tanel Teemusk

Passing variables to a function

My lingo is so Actionscript, but that is changing slowly. Variables are methods, and we’re actually passing properties in Objective-C. But ok. Yesterday I wrote about declaring and calling functions/methods in Objective-C. Now I’ll try to explain how to declare functions that accept variables and how to pass variables to them. Also I cover briefly how to get ‘trace’ statements in Objective C.

So let’s cut to the chase.

Trace Statements

Actionscript:

var string:String = "I AM STRING";
trace("I am getting traced in the console ");
trace("I am a variable: "+string);

Objective-C

NSString *string = @"I AM STRING";
NSLog(@"I am getting traced in the console");
NSLog(@"I am a variable %@",string);

Now note how variables work in NSLog statements. characters starting with % sign will get substituted by comma separated variables. Also all string defined have to have “@” in front of them.
They’re a bit to get used to. I will pass a cheatsheet of different variables

Actionscript

private function myFunction(foo:String){
trace("I got the variable "+foo);
}

 Passing a variable to a function

Passing a var to a function in Actionscript:

private firstFunction():void{
var str:String = "This is passed data";
anotherFunction(str);
}
private anotherFunction(s:String):void{
trace(s); //Output: This is passed data
}

Passing a variable to a function with Objective-C:

//First add this line to your header (.h) file;
- (void)anotherFunction:(NSString *)s;

//then in Class file (.m) you can call this function like so:
-(void)firstFunction{
NSString *str = @"This is passed data";
[self anotherFunction:str];
}
- (void)anotherFunction:(NSString *)s{
NSLog(@"%@",s); //Output This is passed data
}

Make sure ‘firstFunction’ is called. Try to use AppDelegate’s initWithOptions as your firstFunction.

Objective C NSLog cheatsheet:

%@     Object
%d, %i signed int
%u     unsigned int
%f     float/double
%x, %X hexadecimal int
%o     octal int
%zu    size_t
%p     pointer
%e     float/double (in scientific notation)
%g     float/double (as %f or %e, depending on value)
%s     C string (bytes)
%S     C string (unichar)
%.*s   Pascal string (requires two arguments, pass pstr[0] as the first, pstr+1 as the second)

%c     character
%C     unichar

%lld   long long
%llu   unsigned long long
%Lf    long double

Tags: actionscript, flash, javascript, learning, objc, objective c

Objective-C Here I come

Okay. I’ve been learning Objective-C on and off for quite a while now. I’ve been doing it mostly using The Big Nerd Ranch books.

I can tell you it has not been easy. While all tutorials in these books are quite straightforward and work out just great when you follow a book, they still haven’t helped me to get my head around this language. I get the syntax, I get how the structure should work, but some of the concepts are so different coming from ECMA script language background such as Actionscript or Javascript. Painful.

Also I have googled around a lot. While there are some blogs that describe a bit about migrating from ECMA script to C based language, they haven’t helped me out too much.

Therefore I will try to add my 5 cents to the blogosphere about this subject. (And don’t judge me if I’m wrong in my theories presented here. I’m just a n00b.).

Declaring and calling a function

This is probably the first thing you want to do. In Actionscript 3 I would do this:

Defining a function:

private myFunction():void{
//Do something;
}

To call this function from another function I would just:

private anotherFunction():void{
myFunction();
}

In Objective C it’s not as straightforward. Defining a function like this won’t allow to call it from another function.

Defining a function:

First add the function description to an interface (yeah that’s the myClass.h file. Objective C calls them Headers).

- (void)myFunction;

Then in the class itself (myClass.m file) define this function completely:

-(void)myFunction{
//Do something
}

And then you can call it from another function:

-(void)anotherFunction{
[self myFunction];
}

 

I hope you get the idea how it works. I will try to add more examples soon.

Tags: actionscript, flash, function, javascript, learning, method, objc, objective c