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I am currently doing the tutorials in the book: "learn iPhone and iPad cocos2d Game Development" by Steffen Itterheim and have been running into problems with the code for the DoodleDrop tutorial, chapter 4. I have tried to find the source of the problem but i am not able to do so.

Here is the code i am using:

#import "GameScene.h"

@implementation GameScene

-(void) spiderBelowScreen:(id)sender {

// Make sure sender is actually of the right class
NSAssert([sender isKindOfClass:[CCSprite class]], @"sender is not a CCSprite!");
CCSprite* spider = (CCSprite*)sender;

// Move the spider back up outside the top of the screen
CGPoint pos = spider.position;
CGSize screenSize = [[CCDirector sharedDirector] winSize];
pos.y = screenSize.height + [spider texture].contentSize.height;
spider.position = pos;

-(void) runSpiderMoveSequence:(CCSprite*)spider {

// Slowly increase the spider speed over time

if (numSpidersMoved % 8 == 0 && spiderMoveDuration > 2.0f) {
    spiderMoveDuration -= 0.1f;

// This is the sequence which controls the spiders' movement
CGPoint belowScreenPosition = CGPointMake(spider.position.x, [spider texture].contentSize.height);
CCMoveTo *move = [CCMoveTo actionWithDuration:spiderMoveDuration position:belowScreenPosition];
CCCallFuncN *call = [CCCallFuncN actionWithTarget:self selector:@selector(spiderBelowScreen)];
CCSequence *sequence = [CCSequence actions:move, call, nil];
[spider runAction:sequence];

-(void) spidersUpdate:(ccTime)delta {

// Try to find a spioder which isn't currently moving
for (int i = 0; i < 10; i++) {
    int randomSpiderIndex = CCRANDOM_0_1() * [spiders count];
    CCSprite *spider = [spiders objectAtIndex:randomSpiderIndex];

    // If the spider isn't moving it won't have any running actions
    if ([spider numberOfRunningActions] == 0) {
        // This is the squense wich controls the spiders' movement
        [self runSpiderMoveSequence:spider];

        // Only onbe spider should start moving at a time

-(void) resetSpiders {

CGSize screenSize = [[CCDirector sharedDirector] winSize];

// Get any spider to get its image width
CCSprite *tempSpider = [spiders lastObject];
CGSize size = [tempSpider texture].contentSize;

int numSpiders = [spiders count];

for (int i = 0; i < numSpiders; i++) {

    // Put each spider at its designated position outside the screen
    CCSprite *spider = [spiders objectAtIndex:i];
    spider.position = CGPointMake(size.width * i + size.width * 0.5f, screenSize.height + size.height);
    [spider stopAllActions];

// Uschedule the selector just in case. If it isn't scheduled it wont do anything
[self unschedule:@selector(spidersUpdate:)];

// Schedule the spider update logic to run at the given interval
[self schedule:@selector(spidersUpdate:) interval:0.7f];

-(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 spider 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 spider array
    [spiders addObject:spider];
// call the method to reposition all spiders
[self resetSpiders];


-(void) update:(ccTime)delta {

// Keep adding up the playerVelocity to the players's position
CGPoint pos = player.position;
pos.x   += playerVelocity.x;

// The player should also be stopped from going outside the screen
CGSize  screenSize  = [[CCDirector sharedDirector] winSize];
float   imageWidthHalved    = [player texture].contentSize.width * 0.5f;
float   leftBorderLimit     = imageWidthHalved;
float   rightBorderLimit    = screenSize.width - imageWidthHalved;

// Preventing the player sprite from moving outside the screen
if (pos.x < leftBorderLimit)
    pos.x   = leftBorderLimit;
    playerVelocity  = CGPointZero;
else if (pos.x > rightBorderLimit)
    pos.x   = rightBorderLimit;
    playerVelocity  = CGPointZero;

player.position = pos;


-(void) accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {

// controls how quickly velocity decelerates (lower = quicker to change direction)
float   deceleration    = 0.2f;

// determines how sensitive the accelerometer reacts (higher = more sensitivity)
float   sensitivity     = 6.0f;

// how fast the velocity can be at most
float   maxVelocity     = 550;

// adjust velocity based on current accelerometer acceleration
playerVelocity.x    = playerVelocity.x * deceleration + acceleration.x * sensitivity;

// we must limit the maximum velocity of the player sprite, in both directions
if (playerVelocity.x > maxVelocity)
    playerVelocity.x    = maxVelocity;
else if (playerVelocity.x < -maxVelocity)
    playerVelocity.x    = -maxVelocity;

+(id)scene {
CCScene *scene = [CCScene node];
CCLayer *layer = [GameScene node];
[scene addChild:layer];
return scene;

-(id)init {
if ((self = [super init])) {
    CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self);

    self.isAccelerometerEnabled = YES;

    player = [CCSprite spriteWithFile:@"alien.png"];
    [self addChild:player z:0 tag:1];

    CGSize screenSize = [[CCDirector sharedDirector] winSize];
    float imageHeight = [player texture].contentSize.height;
    player.position = CGPointMake(screenSize.width / 2, imageHeight / 2);

    // scheduling the update method in order to adjust the player's speed every frame
    [self scheduleUpdate];
    [self initSpiders];

return self;

-(void) deallaoc {
CCLOG(@"%@: %@", NSStringFromSelector(_cmd), self);

// The spiders array must be released, it was created using [CCArray alloc]
[spiders release];
spiders = nil;

// Never forget to call [super dealloc]
[super dealloc];


The result i get (edited), including the NSLog i have included, is:

2011-08-13 15:18:38.401 DoodleDrop[1751:707] >>update:(ccTime)delta<<
2011-08-13 15:18:38.404 DoodleDrop[1751:707] -[GameScene spiderBelowScreen]: unrecognized selector sent to instance 0x257f50
2011-08-13 15:18:38.407 DoodleDrop[1751:707] >>accelerometer<<
2011-08-13 15:18:38.417 DoodleDrop[1751:707] >>update:(ccTime)delta<<
2011-08-13 15:18:38.419 DoodleDrop[1751:707] -[GameScene spiderBelowScreen]: unrecognized selector sent to instance 0x257f50

I wonder if there is someone nice that can help me here?

share|improve this question
You forgot a colon in the selector's name. Basic programming questions should go to Stack Overflow. –  user744 Aug 13 '11 at 14:28
sorry for that Joe, as it is about Cocos2D i did put it here. –  PeterK Aug 13 '11 at 16:07
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1 Answer

up vote 4 down vote accepted

I think you need to use @selector(spiderBelowScreen:). Note the :.

share|improve this answer
(I checked my copy of the book, and it has the colon.) –  user744 Aug 13 '11 at 19:19
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