DynamListView.java

public class DynamicListView extends ListView {

    final static String TAG = DynamicListView.class.getSimpleName();

    private final int SMOOTH_SCROLL_AMOUNT_AT_EDGE = 15;
    private final int MOVE_DURATION = 150;
    private final int LINE_THICKNESS = 15;

    public ArrayList<String> mCheeseList;

    private int mLastEventY = -1;

    private int mDownY = -1;
    private int mDownX = -1;

    private int mTotalOffset = 0;

    private boolean mCellIsMobile = false;
    private boolean mIsMobileScrolling = false;
    private int mSmoothScrollAmountAtEdge = 0;

    private final int INVALID_ID = -1;
    private long mAboveItemId = INVALID_ID;
    private long mMobileItemId = INVALID_ID;
    private long mBelowItemId = INVALID_ID;

    private BitmapDrawable mHoverCell;
    private Rect mHoverCellCurrentBounds;
    private Rect mHoverCellOriginalBounds;

    private final int INVALID_POINTER_ID = -1;
    private int mActivePointerId = INVALID_POINTER_ID;

    private boolean mIsWaitingForScrollFinish = false;
    private int mScrollState = OnScrollListener.SCROLL_STATE_IDLE;

    public DynamicListView(Context context) {
        super(context);
        init(context);
    }

    public DynamicListView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context);
    }

    public DynamicListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public void init(Context context) {
        setOnItemLongClickListener(mOnItemLongClickListener);
        setOnScrollListener(mScrollListener);
        DisplayMetrics metrics = context.getResources().getDisplayMetrics();
        mSmoothScrollAmountAtEdge = (int)(SMOOTH_SCROLL_AMOUNT_AT_EDGE / metrics.density);
    }

    /**
     * Listens for long clicks on any mItems in the listview. When a cell has
     * been selected, the hover cell is created and set up.
     */
    private OnItemLongClickListener mOnItemLongClickListener =
            new OnItemLongClickListener() {
                public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int pos, long id) {
                    mTotalOffset = 0;

                    int position = pointToPosition(mDownX, mDownY);
                    int itemNum = position - getFirstVisiblePosition();

                    View selectedView = getChildAt(itemNum);
                    mMobileItemId = getAdapter().getItemId(position);
                    mHoverCell = getAndAddHoverView(selectedView);
                    selectedView.setVisibility(INVISIBLE);

                    mCellIsMobile = true;

                    updateNeighborViewsForID(mMobileItemId);

                    return true;
                }
            };

    /**
     * Creates the hover cell with the appropriate bitmap and of appropriate
     * size. The hover cell's BitmapDrawable is drawn on top of the bitmap every
     * single time an invalidate call is made.
     */
    private BitmapDrawable getAndAddHoverView(View v) {

        int w = v.getWidth();
        int h = v.getHeight();
        int top = v.getTop();
        int left = v.getLeft();

        Bitmap b = getBitmapWithBorder(v);

        BitmapDrawable drawable = new BitmapDrawable(getResources(), b);

        mHoverCellOriginalBounds = new Rect(left, top, left + w, top + h);
        mHoverCellCurrentBounds = new Rect(mHoverCellOriginalBounds);

        drawable.setBounds(mHoverCellCurrentBounds);

        return drawable;
    }

    /** Draws a black border over the screenshot of the view passed in. */
    private Bitmap getBitmapWithBorder(View v) {
        Bitmap bitmap = getBitmapFromView(v);
        Canvas can = new Canvas(bitmap);

        Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());

        Paint paint = new Paint();
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(LINE_THICKNESS);
        paint.setColor(Color.BLACK);

        can.drawBitmap(bitmap, 0, 0, null);
        can.drawRect(rect, paint);

        return bitmap;
    }

    /** Returns a bitmap showing a screenshot of the view passed in. */
    private Bitmap getBitmapFromView(View v) {
        Bitmap bitmap = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas (bitmap);
        v.draw(canvas);
        return bitmap;
    }

    /**
     * Stores a reference to the views above and below the item currently
     * corresponding to the hover cell. It is important to note that if this
     * item is either at the top or bottom of the list, mAboveItemId or mBelowItemId
     * may be invalid.
     */
    private void updateNeighborViewsForID(long itemID) {
        int position = getPositionForID(itemID);
        ItemsArrayAdapter adapter = ((ItemsArrayAdapter)getAdapter());
        mAboveItemId = adapter.getItemId(position - 1);
        mBelowItemId = adapter.getItemId(position + 1);
    }

    /** Retrieves the view in the list corresponding to itemID */
    public View getViewForID (long itemID) {
        int firstVisiblePosition = getFirstVisiblePosition();
        ItemsArrayAdapter adapter = ((ItemsArrayAdapter)getAdapter());
        for(int i = 0; i < getChildCount(); i++) {
            View v = getChildAt(i);
            int position = firstVisiblePosition + i;
            long id = adapter.getItemId(position);
            if (id == itemID) {
                return v;
            }
        }
        return null;
    }

    /** Retrieves the position in the list corresponding to itemID */
    public int getPositionForID (long itemID) {
        View v = getViewForID(itemID);
        if (v == null) {
            return -1;
        } else {
            return getPositionForView(v);
        }
    }

    /**
     *  dispatchDraw gets invoked when all the child views are about to be drawn.
     *  By overriding this method, the hover cell (BitmapDrawable) can be drawn
     *  over the listview's mItems whenever the listview is redrawn.
     */
    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        if (mHoverCell != null) {
            mHoverCell.draw(canvas);
        }
    }

    @Override
    public boolean onTouchEvent (MotionEvent event) {

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                mDownX = (int)event.getX();
                mDownY = (int)event.getY();
                mActivePointerId = event.getPointerId(0);
                break;
            case MotionEvent.ACTION_MOVE:
                if (mActivePointerId == INVALID_POINTER_ID) {
                    break;
                }

                int pointerIndex = event.findPointerIndex(mActivePointerId);

                mLastEventY = (int) event.getY(pointerIndex);
                int deltaY = mLastEventY - mDownY;

                if (mCellIsMobile) {
                    mHoverCellCurrentBounds.offsetTo(mHoverCellOriginalBounds.left,
                            mHoverCellOriginalBounds.top + deltaY + mTotalOffset);
                    mHoverCell.setBounds(mHoverCellCurrentBounds);
                    invalidate();

                    handleCellSwitch();

                    mIsMobileScrolling = false;
                    handleMobileCellScroll();

                    return false;
                }
                break;
            case MotionEvent.ACTION_UP:
                touchEventsEnded();
                break;
            case MotionEvent.ACTION_CANCEL:
                touchEventsCancelled();
                break;
            case MotionEvent.ACTION_POINTER_UP:
                /* If a multitouch event took place and the original touch dictating
                 * the movement of the hover cell has ended, then the dragging event
                 * ends and the hover cell is animated to its corresponding position
                 * in the listview. */
                pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
                        MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                final int pointerId = event.getPointerId(pointerIndex);
                if (pointerId == mActivePointerId) {
                    touchEventsEnded();
                }
                break;
            default:
                break;
        }

        return super.onTouchEvent(event);
    }

    /**
     * This method determines whether the hover cell has been shifted far enough
     * to invoke a cell swap. If so, then the respective cell swap candidate is
     * determined and the data set is changed. Upon posting a notification of the
     * data set change, a layout is invoked to place the cells in the right place.
     * Using a ViewTreeObserver and a corresponding OnPreDrawListener, we can
     * offset the cell being swapped to where it previously was and then animate it to
     * its new position.
     */
    private void handleCellSwitch() {
        final int deltaY = mLastEventY - mDownY;
        int deltaYTotal = mHoverCellOriginalBounds.top + mTotalOffset + deltaY;

        View belowView = getViewForID(mBelowItemId);
        View mobileView = getViewForID(mMobileItemId);
        View aboveView = getViewForID(mAboveItemId);

        boolean isBelow = (belowView != null) && (deltaYTotal > belowView.getTop());
        boolean isAbove = (aboveView != null) && (deltaYTotal < aboveView.getTop());

        if (isBelow || isAbove) {

            final long switchItemID = isBelow ? mBelowItemId : mAboveItemId;
            View switchView = isBelow ? belowView : aboveView;
            final int originalItem = getPositionForView(mobileView);

            if (switchView == null) {
                updateNeighborViewsForID(mMobileItemId);
                return;
            }

            swapElements(mCheeseList, originalItem, getPositionForView(switchView));

            ((BaseAdapter) getAdapter()).notifyDataSetChanged();

            mDownY = mLastEventY;

            final int switchViewStartTop = switchView.getTop();

            if (android.os.Build.VERSION.SDK_INT <= android.os.Build.VERSION_CODES.KITKAT){
                mobileView.setVisibility(View.VISIBLE);
                switchView.setVisibility(View.INVISIBLE);
            } else{
                mobileView.setVisibility(View.INVISIBLE);
                switchView.setVisibility(View.VISIBLE);
            }

            updateNeighborViewsForID(mMobileItemId);

            final ViewTreeObserver observer = getViewTreeObserver();
            observer.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
                public boolean onPreDraw() {
                    observer.removeOnPreDrawListener(this);

                    View switchView = getViewForID(switchItemID);

                    mTotalOffset += deltaY;

                    Log.v(TAG, "switchview isnull=" + (switchView==null));
                    int switchViewNewTop = switchView.getTop();
                    int delta = switchViewStartTop - switchViewNewTop;

                    switchView.setTranslationY(delta);

                    ObjectAnimator animator = ObjectAnimator.ofFloat(switchView,
                            View.TRANSLATION_Y, 0);
                    animator.setDuration(MOVE_DURATION);
                    animator.start();

                    return true;
                }
            });
        }
    }

    private void swapElements(ArrayList arrayList, int indexOne, int indexTwo) {
        Object temp = arrayList.get(indexOne);
        arrayList.set(indexOne, arrayList.get(indexTwo));
        arrayList.set(indexTwo, temp);
    }


    /**
     * Resets all the appropriate fields to a default state while also animating
     * the hover cell back to its correct location.
     */
    private void touchEventsEnded () {
        final View mobileView = getViewForID(mMobileItemId);
        if (mCellIsMobile|| mIsWaitingForScrollFinish) {
            mCellIsMobile = false;
            mIsWaitingForScrollFinish = false;
            mIsMobileScrolling = false;
            mActivePointerId = INVALID_POINTER_ID;

            // If the autoscroller has not completed scrolling, we need to wait for it to
            // finish in order to determine the final location of where the hover cell
            // should be animated to.
            if (mScrollState != OnScrollListener.SCROLL_STATE_IDLE) {
                mIsWaitingForScrollFinish = true;
                return;
            }

            mHoverCellCurrentBounds.offsetTo(mHoverCellOriginalBounds.left, mobileView.getTop());

            ObjectAnimator hoverViewAnimator = ObjectAnimator.ofObject(mHoverCell, "bounds",
                    sBoundEvaluator, mHoverCellCurrentBounds);
            hoverViewAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator valueAnimator) {
                    invalidate();
                }
            });
            hoverViewAnimator.addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationStart(Animator animation) {
                    setEnabled(false);
                }

                @Override
                public void onAnimationEnd(Animator animation) {
                    mAboveItemId = INVALID_ID;
                    mMobileItemId = INVALID_ID;
                    mBelowItemId = INVALID_ID;
                    mobileView.setVisibility(VISIBLE);
                    mHoverCell = null;
                    setEnabled(true);
                    invalidate();
                }
            });
            hoverViewAnimator.start();
        } else {
            touchEventsCancelled();
        }
    }

    /**
     * Resets all the appropriate fields to a default state.
     */
    private void touchEventsCancelled () {
        View mobileView = getViewForID(mMobileItemId);
        if (mCellIsMobile) {
            mAboveItemId = INVALID_ID;
            mMobileItemId = INVALID_ID;
            mBelowItemId = INVALID_ID;
            mobileView.setVisibility(VISIBLE);
            mHoverCell = null;
            invalidate();
        }
        mCellIsMobile = false;
        mIsMobileScrolling = false;
        mActivePointerId = INVALID_POINTER_ID;
    }

    /**
     * This TypeEvaluator is used to animate the BitmapDrawable back to its
     * final location when the user lifts his finger by modifying the
     * BitmapDrawable's bounds.
     */
    private final static TypeEvaluator<Rect> sBoundEvaluator = new TypeEvaluator<Rect>() {
        public Rect evaluate(float fraction, Rect startValue, Rect endValue) {
            return new Rect(interpolate(startValue.left, endValue.left, fraction),
                    interpolate(startValue.top, endValue.top, fraction),
                    interpolate(startValue.right, endValue.right, fraction),
                    interpolate(startValue.bottom, endValue.bottom, fraction));
        }

        public int interpolate(int start, int end, float fraction) {
            return (int)(start + fraction * (end - start));
        }
    };

    /**
     *  Determines whether this listview is in a scrolling state invoked
     *  by the fact that the hover cell is out of the bounds of the listview;
     */
    private void handleMobileCellScroll() {
        mIsMobileScrolling = handleMobileCellScroll(mHoverCellCurrentBounds);
    }

    /**
     * This method is in charge of determining if the hover cell is above
     * or below the bounds of the listview. If so, the listview does an appropriate
     * upward or downward smooth scroll so as to reveal new mItems.
     */
    public boolean handleMobileCellScroll(Rect r) {
        int offset = computeVerticalScrollOffset();
        int height = getHeight();
        int extent = computeVerticalScrollExtent();
        int range = computeVerticalScrollRange();
        int hoverViewTop = r.top;
        int hoverHeight = r.height();

        if (hoverViewTop <= 0 && offset > 0) {
            smoothScrollBy(-mSmoothScrollAmountAtEdge, 0);
            return true;
        }

        if (hoverViewTop + hoverHeight >= height && (offset + extent) < range) {
            smoothScrollBy(mSmoothScrollAmountAtEdge, 0);
            return true;
        }

        return false;
    }

    public void setCheeseList(ArrayList<String> cheeseList) {
        mCheeseList = cheeseList;
    }

    /**
     * This scroll listener is added to the listview in order to handle cell swapping
     * when the cell is either at the top or bottom edge of the listview. If the hover
     * cell is at either edge of the listview, the listview will begin scrolling. As
     * scrolling takes place, the listview continuously checks if new cells became visible
     * and determines whether they are potential candidates for a cell swap.
     */
    private OnScrollListener mScrollListener = new OnScrollListener () {

        private int mPreviousFirstVisibleItem = -1;
        private int mPreviousVisibleItemCount = -1;
        private int mCurrentFirstVisibleItem;
        private int mCurrentVisibleItemCount;
        private int mCurrentScrollState;

        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                             int totalItemCount) {
            mCurrentFirstVisibleItem = firstVisibleItem;
            mCurrentVisibleItemCount = visibleItemCount;

            mPreviousFirstVisibleItem = (mPreviousFirstVisibleItem == -1) ? mCurrentFirstVisibleItem
                    : mPreviousFirstVisibleItem;
            mPreviousVisibleItemCount = (mPreviousVisibleItemCount == -1) ? mCurrentVisibleItemCount
                    : mPreviousVisibleItemCount;

            checkAndHandleFirstVisibleCellChange();
            checkAndHandleLastVisibleCellChange();

            mPreviousFirstVisibleItem = mCurrentFirstVisibleItem;
            mPreviousVisibleItemCount = mCurrentVisibleItemCount;
        }

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            mCurrentScrollState = scrollState;
            mScrollState = scrollState;
            isScrollCompleted();
        }

        /**
         * This method is in charge of invoking 1 of 2 actions. Firstly, if the listview
         * is in a state of scrolling invoked by the hover cell being outside the bounds
         * of the listview, then this scrolling event is continued. Secondly, if the hover
         * cell has already been released, this invokes the animation for the hover cell
         * to return to its correct position after the listview has entered an idle scroll
         * state.
         */
        private void isScrollCompleted() {
            if (mCurrentVisibleItemCount > 0 && mCurrentScrollState == SCROLL_STATE_IDLE) {
                if (mCellIsMobile && mIsMobileScrolling) {
                    handleMobileCellScroll();
                } else if (mIsWaitingForScrollFinish) {
                    touchEventsEnded();
                }
            }
        }

        /**
         * Determines if the listview scrolled up enough to reveal a new cell at the
         * top of the list. If so, then the appropriate parameters are updated.
         */
        public void checkAndHandleFirstVisibleCellChange() {
            if (mCurrentFirstVisibleItem != mPreviousFirstVisibleItem) {
                if (mCellIsMobile && mMobileItemId != INVALID_ID) {
                    updateNeighborViewsForID(mMobileItemId);
                    handleCellSwitch();
                }
            }
        }

        /**
         * Determines if the listview scrolled down enough to reveal a new cell at the
         * bottom of the list. If so, then the appropriate parameters are updated.
         */
        public void checkAndHandleLastVisibleCellChange() {
            int currentLastVisibleItem = mCurrentFirstVisibleItem + mCurrentVisibleItemCount;
            int previousLastVisibleItem = mPreviousFirstVisibleItem + mPreviousVisibleItemCount;
            if (currentLastVisibleItem != previousLastVisibleItem) {
                if (mCellIsMobile && mMobileItemId != INVALID_ID) {
                    updateNeighborViewsForID(mMobileItemId);
                    handleCellSwitch();
                }
            }
        }
    };
}