Box2D getPosotion error Thread 1: EXC_BAD_ACCESS iPhone - ios

Question

I am working on a game . I am facing problem in box2d.
I have created a World and a Web (sprite,body) and then i am throwing web on touchend, and a tick selector which gets position of sprite and its giving error.
Here is tick selector
onTouchEnd
- (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{
if (freeBody) {
[self schedule: #selector(tick:)];
[self schedule:#selector(WebHitsFood:) interval:0.01f];
freeBody->SetType(b2_dynamicBody);
//this is the maximum force that can be applied
const CGFloat maxForce = 600;
//get the location of the end point of the swipe
UITouch *myTouch = [touches anyObject];
CGPoint location = [myTouch locationInView:[myTouch view]];
location = [[CCDirector sharedDirector] convertToGL:location];
//get the rotation b/w the start point and the end point
CGFloat rotAngle = atan2f(location.y - startPoint.y,location.x - startPoint.x);
//the distance of the swipe if the force
CGFloat distance = ccpDistance(startPoint, location) * 0.5;
//put a cap on the force, too much of it will break the rope
if (distance>maxForce) distance = maxForce;
//apply force
freeBody->ApplyForce(b2Vec2(cosf(rotAngle) * distance, sinf(rotAngle) * distance), freeBody->GetPosition());
//lose the weak reference to the body for next time usage.
freeBody = nil;
}
self.isTouchEnabled = NO;
}
and Create Web Method
-(void) createWeb
{
freeBodySprite = [CCSprite spriteWithFile:#"web1.png"];//web_ani_6_1
//freeBodySprite.position = ccp(100, 300);
[self addChild:freeBodySprite z:2 tag:6];
CGPoint startPos = CGPointMake(100, 320/1.25);
bodyDef.type = b2_staticBody;
bodyDef.position = [self toMeters:startPos];
bodyDef.userData = freeBodySprite;
float radiusInMeters = ((freeBodySprite.contentSize.width * freeBodySprite.scale/PTM_RATIO) * 0.5f);
shape.m_radius = radiusInMeters;
fixtureDef.shape = &shape;
fixtureDef.density = 0.5f;
fixtureDef.friction = 1.0f;
fixtureDef.restitution = 0.0f;
circularObstacleBody = world->CreateBody(&bodyDef);
stoneFixture = circularObstacleBody->CreateFixture(&fixtureDef);
freeBody = circularObstacleBody;
}

Answer 1

Are you sure the GetPosition() is the problem? Try adding the line
float test = b->GetPosition().x;
just before the one giving you the issue to determine whether the issue is actually with GetPosition() or whether it is the myActor.position that is the source of the exc_bad_access.

Answer 2

Easy way to fix that crash:
for(b2Body* b= world->GetBodyList(); b; B->GetNext())
{
id sprite = b->GetUserData();
if( sprite && [sprite isKindOfClass:[CCSprite class])
{
CCSprite *myActor = (CCSprite*) sprite;
myActor.position = CGPointMake(b->getPosition().x*PTM_RATIO, b->getPosition().y*PTM_RATIO);
myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}