Bodies do not collide

i have set 2 bodies, a world with gravity,a tick method with step,and all the bodies are moving just fine,and i can apply forces on them, gravity is also working.

but no collision. when body1 hit the ground he just go out of screen and not hit it and jump like a real ball. when body1 hit body2 the just continue movement as nothing was happen.

the bodies have shape ,the world have edges, but no collision. what am i missing here ?

here are some functions that i call from the init :

- (void)addBoxBodyForSprite:(CCSprite *)sprite {

    b2BodyDef spriteBodyDef;
    spriteBodyDef.type = b2_dynamicBody;
    spriteBodyDef.position.Set(sprite.position.x/PTM_RATIO,sprite.position.y/PTM_RATIO);
    spriteBodyDef.userData = sprite;
    spriteBody = world->CreateBody(&spriteBodyDef);

    b2PolygonShape spriteShape;
    spriteShape.SetAsBox(sprite.contentSize.width/PTM_RATIO/2,sprite.contentSize.height/PTM_RATIO/2);
    b2FixtureDef spriteShapeDef;
    spriteShapeDef.shape = &spriteShape;
    spriteShapeDef.density = 10.0;
    spriteShapeDef.isSensor = true;
    spriteBody->CreateFixture(&spriteShapeDef);

}


-(void)worldEdge
{
    CGSize winSize = [CCDirector sharedDirector].winSize;
    b2BodyDef groundBodyDef;
    groundBodyDef.position.Set(0,0);
    b2Body *groundBody = world->CreateBody(&groundBodyDef);
    b2PolygonShape groundBox;
    b2FixtureDef boxShapeDef;
    boxShapeDef.shape = &groundBox;
    groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(winSize.width/PTM_RATIO, 0));
    groundBody->CreateFixture(&boxShapeDef);
    groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(0, winSize.height/PTM_RATIO));
    groundBody->CreateFixture(&boxShapeDef);
    groundBox.SetAsEdge(b2Vec2(0, winSize.height/PTM_RAT开发者_开发技巧IO), b2Vec2(winSize.width/PTM_RATIO, winSize.height/PTM_RATIO));
    groundBody->CreateFixture(&boxShapeDef);
    groundBox.SetAsEdge(b2Vec2(winSize.width/PTM_RATIO, winSize.height/PTM_RATIO), b2Vec2(winSize.width/PTM_RATIO, 0));
    groundBody->CreateFixture(&boxShapeDef);
}




-(void)tick:(ccTime) dt
{


    world->Step(dt,10,10);
    for(b2Body *b=world->GetBodyList(); b; b=b->GetNext()) 
    {
        if(b->GetUserData() !=NULL )
           {
               CCSprite *sprite=(CCSprite *) b->GetUserData();//every b of the world will be update his position
               sprite.position=ccp( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO  ) ;
               sprite.rotation=-1*CC_RADIANS_TO_DEGREES(b->GetAngle());
           }

    }

everything is moving allright but no collision ever.

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The specific problem is this line:

spriteShapeDef.isSensor = true;

In box2d, when you set an fixture as a sensor, it will not collide with other fixtures.