MyScene.m

- (void)addMole
{
    NSLog(@"%s", __func__);

    // 今動いていないもぐらのインデックスの配列を作る
    NSMutableArray *targetMolesIndex = [NSMutableArray array];
    for(int i = 0; i < moles_.count; i++){
        NSObject *object = moles_[i];
        if(object == [NSNull null]){
            [targetMolesIndex addObject:@(i)];
        }
    }

    NSLog(@"targetMolesIndex.count = %d", targetMolesIndex.count);
    
    // すべてのもぐらが動いていたら、何もしない
    if(targetMolesIndex.count == 0){
        return;
    }

    // もぐらを出す穴のインデックスを決定
    NSNumber *index = targetMolesIndex[arc4random() % targetMolesIndex.count];

    // もぐらのスプライトを作る
    SKSpriteNode *mole = [SKSpriteNode spriteNodeWithImageNamed:@"Mole"];
    mole.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:mole.size.width / 2];
    mole.physicsBody.affectedByGravity = NO;
    mole.name = kMoleName;

    // 配列に保存しておく
    moles_[index.integerValue] = mole;
    
    int x = index.integerValue % 3;
    int y = index.integerValue / 3;
//    SKSpriteNode *ground1 = [self childNodeWithName:kGround1Name];
    SKSpriteNode *ground2 = (SKSpriteNode*)[self childNodeWithName:kGround2Name];
    SKSpriteNode *ground3 = (SKSpriteNode*)[self childNodeWithName:kGround3Name];
    SKSpriteNode *ground4 = (SKSpriteNode*)[self childNodeWithName:kGround4Name];
    CGFloat positionX = ground2.position.x + ground2.size.width/4*(-1+x);
    CGFloat positionY = 0;
    NSLog(@"%f %f", positionX, positionY);

    switch (y) {
        case 0:
            positionY = ground2.position.y;
            break;
        case 1:
            positionY = ground3.position.y;
            break;
        case 2:
            positionY = ground4.position.y;
            break;
        default:
            break;
    }
    
    mole.position = CGPointMake(positionX,
                                positionY);
    if(index.integerValue < 3){
        mole.zPosition = 0.15;
    }
    else if(index.integerValue < 6){
        mole.zPosition = 0.25;
    }
    else if(index.integerValue < 9){
        mole.zPosition = 0.35;
    }
    
    [self addChild:mole];
    
    // もぐらを動かす
    SKAction *moveUp = [SKAction moveBy:CGVectorMake(0, mole.size.height*0.9)
                               duration:0.5];
    SKAction *wait = [SKAction waitForDuration:skRand(0.5, 2.0)];
    SKAction *moveDown = [SKAction moveBy:CGVectorMake(0, -mole.size.height*0.9)
                                 duration:0.5];
    SKAction *block = [SKAction runBlock:^{
        [mole removeFromParent];
        moles_[index.integerValue] = [NSNull null];
    }];
    SKAction *seq = [SKAction sequence:@[moveUp, wait, moveDown, block]];
    [mole runAction:seq];
}