如何知道身体在Andengine的manageupdate中的先前位置？

Question

I wanted to know the difference of position from one update to another

Relevant code:

 @Override
        protected void onManagedUpdate(float pSecondsElapsed) {
            super.onManagedUpdate(pSecondsElapsed);                

                    Log.d("bar move", "fuel: "+ Float.toString(walkingFuel)) ;
                    if(counter==5) {    // each time is to fast to percive difference?
                         Log.d("bar move", "previous x : "+ Float.toString(previousPosition.x)) ;
                         Log.d("bar move", "current x : "+ Float.toString(PlayerBody.getPosition().x)) ;

                         Log.d("bar move", "fuel consumed: "+ Float.toString( Math.abs(previousPosition.x - PlayerBody.getPosition().x) * 5));
                         walkingFuel += Math.abs(PlayerBody.getPosition().x - previousPosition.x  ) * 5.0f;
                         previousPosition = PlayerBody.getPosition();
                         Log.d("bar move", "current fuel : "+ Float.toString(walkingFuel)) ;

                         counter=0;
                    }
                    counter++; }

I thought that the diference from each manageupdate was to low to percive difference, thats why the counter. Any how, in each maneageUpdate both previous and current are equal.

Here is a bit of my log to make it simpler

fuel: 0.0

previous x : 6.8613663

current x : 6.8613663

fuel consumed: 0.0

current fuel : 0.0

Later

fuel: 0.0

previous x : 7.0288167

current x : 7.0288167

fuel consumed: 0.0

current fuel : 0.0

So, I did something wrong here? If so, whats the right way of doing it?

Answer 1

previousPosition = PlayerBody.getPosition();

Probably here you just copy the reference to the object but not the value. You need to copy the value. May be something like this:

previousPosition = new Vector2(PlayerBody.getPosition().x, PlayerBody.getPosition().y);

I don't remember what type you should use for storing position in andEngine, so change the type to the type of "previousPosition".