No visible #interface for 'class' declares the selector 'selector' - cocos2d-iphone

Question

I'm following "Learn Cocos2D" and in chapter 4 I'm met with the following directive:
And in the GameLayer init method, add the call to the initSpiders method discussed next, right after scheduleUpdate:
-(id) init {
if ((self=[super init])) {
...
[self scheduleUpdate];
[self initSpiders];
}
return self;
}
I get and ARC error message: no visible #interface for 'GameLayer' declares the selector 'initSpiders'
I get the same message at the line: self resetSpiders
what am i missing? everything builds and runs great up to that point.

Answer 1

This issue derives from the fact that the initSpiders and resetSpiders are not declared in your class interface and are defined in the .m file after the point where they are used.
If they are not missing altogether, you can fix this in either of 2 ways:
move the definition of the initSpiders and resetSpiders methods above your init method and the errors will disappear;
add a declaration for both methods in the #interface of the class.
(If you do both, it will also work)
Check your code to see if the implementation for those methods is available.

Answer 2

Your error appears to be that you haven't followed the next bit of the book too. Completing the next section should allow you to compile your code without warnings like this.
A more complete extract of that section of the book is:
And in the GameScene init method add the call to the initSpiders method discussed next, right after scheduleUpdate:
-(id) init {
if ((self = [super init]))
{
… 96 CHAPTER 4: Your First Game
[self scheduleUpdate];
[self initSpiders];
}
return self;
}
After that a fair bit of code is added to the GameScene class, beginning with the initSpiders method in Listing 4–8, which is creating the spider sprites.
Listing 4–8. For Easier Access, Spider Sprites Are Initialized and Added to a CCArray
-(void) initSpiders
{
CGSize screenSize = [[CCDirector sharedDirector] winSize];
// using a temporary spider sprite is the easiest way to get the image's size
CCSprite* tempSpider = [CCSprite spriteWithFile:#"spider.png"];
float imageWidth = [tempSpider texture].contentSize.width;
// Use as many spiders as can fit next to each other over the whole screen width.
int numSpiders = screenSize.width / imageWidth;
// Initialize the spiders array using alloc.
spiders = [[CCArray alloc] initWithCapacity:numSpiders];
for (int i = 0; i < numSpiders; i++)
{
CCSprite* spider = [CCSprite spriteWithFile:#"spider.png"];
[self addChild:spider z:0 tag:2];
// Also add the spider to the spiders array.
[spiders addObject:spider];
}
// call the method to reposition all spiders
[self resetSpiders];
}