macOS Image array with Obj-C

[Hot Sauce79]

How would i go about creating and working with an image array in Obj-C in Xcode?

I need to know how to create the array to be 10 by 20 and i need to be able to swap in and out images in the array. (Images are 20 x 20 pixels if that matters)

I will swap the images using if statements of course, but I do not know/can not find the syntax for working with arrays in Obj-C.

Any and all help is appreciated.

 

[Eraserhead]

Look at NSMutableArray.

 

[Hot Sauce79]

Ok i understand how to declare them now... all except for one part that is.

here is kinda of what i want to do in Xcode with C++ syntax

int Array[10][20];

...
array[0][19] = blueimage;
array[0][18] = redimage;
array[0][17] = blueimage;
array[0][16] = greenimage;
...
array[0][1] = blueimage;
array[0][0] = greenimage;
...


for (i=0; i<=9; i++){
array[0][x]=blackimage;
x=x+1;
y=25;
}

if (y=25)
{
code that changes all of array[0][...] to array[1][...]
}

That isnt exactly what I am needing to do, but if i knew how to do all of that in Xcode then I would be able to figure the rest out on my own.

I think I just need to learn how to make multiple indexes for a single object in the array but i can't find any syntax for it. =/ i looked at that page that you provided but I couldn't find it on there.

 

[yeroen]

C-style arrays in Obj-C are exactly the same as arrays in C. However, I'd closely follow the advice not to use built in C-arrays for objects of class (or NSObject derived) type. There are many pitfalls in doing so (lookup 'never treat arrays polymorphically' in google).

As a previous poster suggested, use NSMutableArray instead.

 

[Hot Sauce79]

ok. I understand.


I also think i might have figured out another way to do it though...

would making an array with 200 indexes and calling a function that translates what i want to happen into the 1-200 number that corresponds with my [0-9][0-19] number work?

im guessing that i could do this by running a computation on it. It seems that it will work well enough.

 

[lee1210]

I think what you want is just to have a multidimensional array. The good news is that NSMutableArray holds NSObjects, and NSMutableArray is an NSObject. The bad news is that this does not guarantee a rectangular matrix. Each of the second-level NSMutableArrays might have a different number of elements, making the array "jagged". You can make it rectangular, it's just not something that can be assumed. You can use -initWithCapacity or +arrayWithCapacity to ensure that the second-level NSMutableArrays are all can contain y elements at instantiation, but note that you must place objects in order from index 0 to index y-1. You would do something like:

NSMutableArray *myArray = [[NSMutableArray alloc] initWithCapacity:20];
for(NSUInteger x=0;x<20;x++) {
  [myArray insertObject:[[NSMutableArray alloc] initWithCapacity:15] atIndex: x];
}
for(NSUInteger x=0;x<20;x++) { 
  for(NSUInteger y=0;y<15;y++) {
    [[myArray objectAtIndex:x] insertObject: [NSNumber numberWithUnsignedInteger:x*15+y] atIndex:y];
  }
}

NSNumber *oneVal = [[myArray objectAtIndex:4] objectAtIndex:5];
NSLog(@"The value is: %@.",oneVal);

The output should be:
The value is 65.

I didn't compile this, but I hope the idea is clear and some of the methods you should use are included. In C this would be similar to:

int myArray[20][15],x,y;
for(x=0;x<20;x++) {
  for(y=0;y<15;y++) {
    myArray[x][y]=x*15+y;
  }
}

Instead you are storing objects instead of primitives, and your arrays can be dynamically resized after the initial setup if needed.

-Lee

 

[Hot Sauce79]

Thank you very much everyone (especially Lee) you all helped me out alot.

 

[lazydog]

C-style arrays in Obj-C are exactly the same as arrays in C. However, I'd closely follow the advice not to use built in C-arrays for objects of class (or NSObject derived) type. There are many pitfalls in doing so (lookup 'never treat arrays polymorphically' in google).

As a previous poster suggested, use NSMutableArray instead.

Hi Yeroen, I understand the problem you mention wrt C++, but I would have thought in this case C style arrays would be fine since the array would really just be an array of typed pointers.

thanks

b e n