Android通过滑动（AndEngine）更改对象位置

Question

I have been developing a game for 2 weeks. I have a ball on center top of device screen. I use swipe for moving it just along X coordinate. I have three cases for this situation.

Case 1: (TouchEvent.ACTION_DOWN) Ball will not move any position.

Case 2: (TouchEvent.ACTION_MOVE) This case is significant for me. If I swipe my finger to right side, ball moves right, If left side.....

Case 3: (TouchEvent.ACTION_UP) The ball falls down with gravity, after it has dynamic body. anyway.

Normally with above three cases, when I swipe my finger on screen, ball immediately comes same x position with my finger. Let me explain this act with an example.

My camera_width is 720. The ball stands on 360. I touch down 480 x position. If I just swipe 2 unit to right, My finger current position will be 482. Problem is that ball jumps to 482. I don't want it.

My move difference is 2 unit. I want it that jumps 362. Here' my code:

    if ( mPhysicsWorld != null && currentBody != null)
    {

        switch ( pSceneTouchEvent.getAction() )
        {
            case TouchEvent.ACTION_DOWN:
                isFirstTouch = true;
                oldLocationX = pSceneTouchEvent.getX();
                newLocationX = pSceneTouchEvent.getX();
                break;

            case TouchEvent.ACTION_MOVE:

                if (  oldLocationX + 30 > pSceneTouchEvent.getX() && pSceneTouchEvent.getX() > oldLocationX - 30 )
                {
                    if ( !isFirstTouch )
                    {
                        if ( newLocationX != pSceneTouchEvent.getX() )
                        {
                            oldLocationX = newLocationX;
                            paddleX = pSceneTouchEvent.getX() + (pSceneTouchEvent.getX() - newLocationX);
                            paddleX = Math.max( paddleX, currentSprite.getWidthScaled() / 2 );
                            paddleX = Math.min( paddleX, CAMERA_WIDTH - currentSprite.getWidthScaled() / 2 );
                            currentBody.setTransform( paddleX / 32, currentBody.getPosition().y, 0 );
                            newLocationX = pSceneTouchEvent.getX();
                        }

                    }
                }
                else
                {
                    isFirstTouch = false;
                    if ( newLocationX != pSceneTouchEvent.getX() )
                    {
                        oldLocationX = newLocationX;
                        paddleX = pSceneTouchEvent.getX() + (pSceneTouchEvent.getX() - newLocationX);
                        paddleX = Math.max( paddleX, currentSprite.getWidthScaled() / 2 );
                        paddleX = Math.min( paddleX, CAMERA_WIDTH - currentSprite.getWidthScaled() / 2 );
                        currentBody.setTransform( paddleX / 32, currentBody.getPosition().y, 0 );
                        newLocationX = pSceneTouchEvent.getX();
                    }
                }

                Log.d( "move", "oldPositionX: " + oldLocationX  + " ");

                break;

            case TouchEvent.ACTION_UP:
                currentBody.setType( BodyDef.BodyType.DynamicBody );
                addFaceInFuture( currentBody );

                break;
        }

Answer 1

try to replace

paddleX = pSceneTouchEvent.getX() + (pSceneTouchEvent.getX() - newLocationX);

with

paddleX = currentBody.getPosition().x + (pSceneTouchEvent.getX() - newLocationX);

another approach would be to save the x position from the event (evtStartX) and the body (bodyStartX) at ACTION_DOWN

At ACTION_MOVE you only need to calculate the difference between the current x position and evtStartX. Then add the result to bodyStartX

case TouchEvent.ACTION_DOWN:
    evtStartX = pSceneTouchEvent.getX();
    bodyStartX = currentBody.getPosition().x
    break;

case TouchEvent.ACTION_MOVE:
    xDif = pSceneTouchEvent.getX() - evtStartX;
    xDif = xDif/32;
    body.setPositon(bodyStartX + xDif, body.getPosition().y);
    break;

Answer 2

I improved my code for my problem. I give you solution at below.

@Override
    public boolean onSceneTouchEvent(Scene pScene, TouchEvent pSceneTouchEvent)
    {

        int eid = pSceneTouchEvent.getAction();
        float leftBorderPosition = currentSprite.getWidthScaled() / 2;
        float rightBorderPosition = CAMERA_WIDTH -         currentSprite.getWidthScaled() / 2;

        if ( mPhysicsWorld != null && currentBody != null)
        {

            switch ( eid )
            {
                case TouchEvent.ACTION_DOWN:
                    oldLocationX = pSceneTouchEvent.getMotionEvent().getX() / 32;
                    break;

                case TouchEvent.ACTION_MOVE:

                    newLocationX = pSceneTouchEvent.getMotionEvent().getX() / 32;
                    if ( pSceneTouchEvent.getMotionEvent().getHistorySize() > 0 )
                    {
                        oldLocationX = pSceneTouchEvent.getMotionEvent().getHistoricalX(0) / 32;
                    }

                    paddleX = (currentBody.getPosition().x + (newLocationX - oldLocationX));
                    paddleX = Math.max( paddleX, (leftBorderPosition / 32) );
                    paddleX = Math.min( paddleX, (rightBorderPosition / 32) );
                    currentBody.setTransform( paddleX, currentBody.getPosition().y, 0 );

                    break;

                case TouchEvent.ACTION_UP:

                    engineLock.lock();
                    currentBody.setType( BodyDef.BodyType.DynamicBody );
                    engineLock.unlock();

                    if ( currentBody.getUserData().equals( "bomb" ) )
                    {
                        /**
                         *
                         *  Bomba su anda aktif ve butun update'ler unregister olsun.
                         *
                         */
                        bombBody = currentBody;
                        bombSprite = currentSprite;
                        mEngine.unregisterUpdateHandler( allBodyIsStoppedIUpdatehandler );
                        mEngine.unregisterUpdateHandler( isBallsReachedLimit );
                        addBallInFuture( null );
                    }
                    else
                    {
                        addBallInFuture( currentBody );
                    }

                    break;
            }

        }

        return false;
    }

TouchEvent.ACTION_DOWN and TouchEvent.ACTION_MOVE cases include the solution. Here is important thing that when we swipe, we have to get differrence between touch position and pre position.