NSArray of UIImage problem

[reisuke]

Hello everyone.
I'm trying to create an array of UIImages using the following code:

NSArray *tutImages = [NSArray arrayWithObjects:
					  [UIImage imageNamed:@"1.png"],
					  [UIImage imageNamed:@"2.png"],
					  nil];

I realize that the array has to be defined within a function, or else the nil produces a "initializer is not a constant" error.

But if it's inside a function, I can't access it on other functions (which I need to do)

How will I go about creating it in a way that is accessible by other functions?
Also, how will I make my ImageView load an object of the array?

Thank you

[Warp]

Well, you could do it like this:

NSArray* images()
{
    static NSArray *tutImages = [[NSArray alloc] initWithObjects:
					  [UIImage imageNamed:@"1.png"],
					  [UIImage imageNamed:@"2.png"],
					  nil];
    return tutImages;
}

and then have all your code call that function. However, the array is never released, which is ugly.

[reisuke]

I see. Is there any other way of doing this?

[Duncan C]

Originally Posted by reisuke

I see. Is there any other way of doing this?

Make the array an instance variable (or property) of your object.

Then assign a value to it in the init method.

[reisuke]

I don't quite understand what you are trying to say.
I don't have any object for this. I just want to make a simple array of images.

[Duncan C]

Originally Posted by reisuke

I don't quite understand what you are trying to say.
I don't have any object for this. I just want to make a simple array of images.

What is the file where you are trying to create the array of objects? Is it a file like myViewController.m? Is the method inside an @implementation... @end block?

If so, you are writing instance methods for some object. Just about all the code you write in Cocoa is instance methods for different objects in your project.

In order to create something like an array that can be shared between different methods, you have to create the array as an instance variable of the object where you want to use it.

[luther_stanton]

Originally Posted by Warp

Well, you could do it like this:

NSArray* images()
{
    static NSArray *tutImages = [[NSArray alloc] initWithObjects:
					  [UIImage imageNamed:@"1.png"],
					  [UIImage imageNamed:@"2.png"],
					  nil];
    return tutImages;
}

and then have all your code call that function. However, the array is never released, which is ugly.

Consider changing the above code to:

NSArray* images()
{
    static NSArray *tutImages = [[[NSArray alloc] initWithObjects:
					  [UIImage imageNamed:@"1.png"],
					  [UIImage imageNamed:@"2.png"],
					  nil]autorelease];
    return tutImages;
}

This will free the memory through the auto-release pool. If the caller needs to maintain a reference to the returned result they would need to user the retain method.

You could also call the convenience constructor on NSArrray - arrayWithObjects to achieve the same result.

[smasher]

Originally Posted by Warp

Well, you could do it like this:

NSArray* images()
{
    static NSArray *tutImages = [[NSArray alloc] initWithObjects:
					  [UIImage imageNamed:@"1.png"],
					  [UIImage imageNamed:@"2.png"],
					  nil];
    return tutImages;
}

and then have all your code call that function. However, the array is never released, which is ugly.

I don't think that'll compile; static variables need to have a constant initializer.

Try this:

-(NSArray*) images{
    static NSArray *tutImages = nil;
    if(tutImages==nil){
        tutImages = [[NSArray alloc] initWithObjects:
					 [UIImage imageNamed:@"1.png"],
					 [UIImage imageNamed:@"2.png"],
					 nil];
    }
    return tutImages;
}

Warp is right though; the images will never get released this way. If that's a problem, better to make it an instance variable (declared in the .h, set in the init method) like Duncan said.

Do not autorelease the array in this case; that pretty much guarantees it'll be gone by the time you go to use it.

[Warp]

Originally Posted by luther_stanton

Consider changing the above code to:

NSArray* images()
{
    static NSArray *tutImages = [[[NSArray alloc] initWithObjects:
					  [UIImage imageNamed:@"1.png"],
					  [UIImage imageNamed:@"2.png"],
					  nil]autorelease];
    return tutImages;
}

This will free the memory through the auto-release pool.

That's a quite heavy way of doing it. Memory allocation is a relatively heavy operation, and the 'imageNamed' method of UIImage is quite a heavy operation. Given that the contents of the array will always be the same, it feels a complete waste of time to allocate all those objects and run all those 'imageNamed' methods every time you need to access the array. It will also potentially worsen memory fragmentation.

[Warp]

Originally Posted by smasher

I don't think that'll compile; static variables need to have a constant initializer.

Change the extension of the source code file from .m to .mm and it will.

[luther_stanton]

Originally Posted by Warp

That's a quite heavy way of doing it. Memory allocation is a relatively heavy operation, and the 'imageNamed' method of UIImage is quite a heavy operation. Given that the contents of the array will always be the same, it feels a complete waste of time to allocate all those objects and run all those 'imageNamed' methods every time you need to access the array. It will also potentially worsen memory fragmentation.

Whoops - the static did not register when I looked at the original post. I agree that using the autorelease pool in this case would not be the best approach - thanks for pointing that out.