DynamicGridView.java

DynamicGridView.java

package com.project.ui.dynamicgridview;


import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.AnimatorSet;
import android.animation.ObjectAnimator;
import android.animation.TypeEvaluator;
import android.annotation.TargetApi;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.os.Build;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Pair;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewTreeObserver;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.ListAdapter;

import com.project.R;
import com.project.util.DeviceUtils;

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Stack;

/**
 * Author: alex askerov
 * Date: 9/6/13
 * Time: 12:31 PM
 */
public class DynamicGridView extends GridView {
    private static final int INVALID_ID = -1;

    private static final int MOVE_DURATION = 300;
    private static final int SMOOTH_SCROLL_AMOUNT_AT_EDGE = 8;

    private BitmapDrawable hoverCell;
    private Rect hoverCellCurrentBounds;
    private Rect hoverCellOriginalBounds;

    private int totalOffsetY = 0;
    private int totalOffsetX = 0;

    private int downX = -1;
    private int downY = -1;
    private int lastEventY = -1;
    private int lastEventX = -1;

    //used to distinguish straight line and diagonal switching
    private int overlapIfSwitchStraightLine;

    private List<Long> idList = new ArrayList<>();

    private long mobileItemId = INVALID_ID;

    private boolean cellIsMobile = false;
    private int activePointerId = INVALID_ID;

    private boolean isMobileScrolling;
    private int smoothScrollAmountAtEdge = 0;
    private boolean isWaitingForScrollFinish = false;
    private int scrollState = OnScrollListener.SCROLL_STATE_IDLE;

    private boolean isEditMode = false;

    private boolean hoverAnimation;
    private boolean reorderAnimation;
    private boolean isEditModeEnabled = true;

    private OnScrollListener userScrollListener;
    private OnDropListener dropListener;
    private OnDragListener dragListener;
    private OnEditModeChangeListener editModeChangeListener;
    private OnSelectedItemDraggableListener selectedItemDraggableListener;

    private OnItemClickListener userItemClickListener;
    private OnItemClickListener localItemClickListener = new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            if (!isEditMode() && isEnabled() && userItemClickListener != null) {
                userItemClickListener.onItemClick(parent, view, position, id);
            }
        }
    };

    private boolean undoSupportEnabled;
    private Stack<DynamicGridModification> modificationStack;
    private DynamicGridModification currentModification;

    private OnSelectedItemBitmapCreationListener selectedItemBitmapCreationListener;
    private View mobileView;


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

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

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

    @Override
    public void setOnScrollListener(OnScrollListener scrollListener) {
        this.userScrollListener = scrollListener;
    }

    public void setOnDropListener(OnDropListener dropListener) {
        this.dropListener = dropListener;
    }

    public void setOnDragListener(OnDragListener dragListener) {
        this.dragListener = dragListener;
    }

    public void setOnSelectedItemDraggableListener(OnSelectedItemDraggableListener listener){
        this.selectedItemDraggableListener = listener;
    }

    /**
     * Start edit mode without starting drag;
     */
    public void startEditMode() {
        startEditMode(-1);
    }

    /**
     * Start edit mode with position. Useful for start edit mode in
     * {@link android.widget.AdapterView.OnItemClickListener}
     * or {@link android.widget.AdapterView.OnItemLongClickListener}
     */
    public void startEditMode(int position) {
        if (!isEditModeEnabled)
            return;
        requestDisallowInterceptTouchEvent(true);

        if (position != -1) {
            startDragAtPosition(position);
        }
        isEditMode = true;
        if (editModeChangeListener != null)
            editModeChangeListener.onEditModeChanged(true);
    }

    public void stopEditMode() {
        isEditMode = false;
        requestDisallowInterceptTouchEvent(false);
        if (editModeChangeListener != null)
            editModeChangeListener.onEditModeChanged(false);
    }

    public boolean isEditModeEnabled() {
        return isEditModeEnabled;
    }

    public void setEditModeEnabled(boolean enabled) {
        this.isEditModeEnabled = enabled;
    }

    public void setOnEditModeChangeListener(OnEditModeChangeListener editModeChangeListener) {
        this.editModeChangeListener = editModeChangeListener;
    }

    public boolean isEditMode() {
        return isEditMode;
    }


    @Override
    public void setOnItemClickListener(OnItemClickListener listener) {
        this.userItemClickListener = listener;
        super.setOnItemClickListener(localItemClickListener);
    }

    public boolean isUndoSupportEnabled() {
        return undoSupportEnabled;
    }

    public void setUndoSupportEnabled(boolean undoSupportEnabled) {
        if (this.undoSupportEnabled != undoSupportEnabled) {
            if (undoSupportEnabled) {
                this.modificationStack = new Stack<>();
            } else {
                this.modificationStack = null;
            }
        }

        this.undoSupportEnabled = undoSupportEnabled;
    }

    public void undoLastModification() {
        if (undoSupportEnabled) {
            if (modificationStack != null && !modificationStack.isEmpty()) {
                DynamicGridModification modification = modificationStack.pop();
                undoModification(modification);
            }
        }
    }

    public void undoAllModifications() {
        if (undoSupportEnabled) {
            if (modificationStack != null && !modificationStack.isEmpty()) {
                while (!modificationStack.isEmpty()) {
                    DynamicGridModification modification = modificationStack.pop();
                    undoModification(modification);
                }
            }
        }
    }

    public boolean hasModificationHistory() {
        if (undoSupportEnabled) {
            if (modificationStack != null && !modificationStack.isEmpty()) {
                return true;
            }
        }
        return false;
    }

    public void clearModificationHistory() {
        modificationStack.clear();
    }

    public void setOnSelectedItemBitmapCreationListener(OnSelectedItemBitmapCreationListener selectedItemBitmapCreationListener) {
        this.selectedItemBitmapCreationListener = selectedItemBitmapCreationListener;
    }

    private void undoModification(DynamicGridModification modification) {
        for (Pair<Integer, Integer> transition : modification.getTransitions()) {
            reorderElements(transition.second, transition.first);
        }
    }

    public void init(Context context) {
        super.setOnScrollListener(scrollListener);
        DisplayMetrics metrics = context.getResources().getDisplayMetrics();
        smoothScrollAmountAtEdge = (int) (SMOOTH_SCROLL_AMOUNT_AT_EDGE * metrics.density + 0.5f);
        overlapIfSwitchStraightLine = getResources().getDimensionPixelSize(R.dimen.overlap_if_switch_straight_line);
    }


    private void reorderElements(int originalPosition, int targetPosition) {
        if (dragListener != null)
            dragListener.onDragPositionsChanged(originalPosition, targetPosition);
        getAdapterInterface().reorderItems(originalPosition, targetPosition);
    }

    private int getColumnCount() {
        return getAdapterInterface().getColumnCount();
    }

    private DynamicGridAdapterInterface getAdapterInterface() {
        return ((DynamicGridAdapterInterface) getAdapter());
    }

    /**
     * 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 = getBitmapFromView(v);

        Bitmap b = createShadowBitmap(v);
        BitmapDrawable drawable = new BitmapDrawable(getResources(), b);

        hoverCellOriginalBounds = new Rect(left, top, left + w, top + h);
        hoverCellCurrentBounds = new Rect(hoverCellOriginalBounds);

        drawable.setBounds(hoverCellCurrentBounds);

        return drawable;
    }

    /**
     * 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;
    }

    /**
     * Returns a bitmap showing a screenshot with shadow of the view passed in.
     */
    private Bitmap createShadowBitmap(View v) {
        Bitmap bitmap = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        v.draw(canvas);
        BlurMaskFilter blurFilter = new BlurMaskFilter(7, BlurMaskFilter.Blur.NORMAL);
        Paint shadowPaint = new Paint();
        shadowPaint.setMaskFilter(blurFilter);

        int[] offsetXY = new int[2];
        Bitmap shadowImage = bitmap.extractAlpha(shadowPaint, offsetXY);

        /* Need to convert shadowImage from 8-bit to ARGB here. */
        Bitmap shadowImage32 = shadowImage.copy(Bitmap.Config.ARGB_8888, true);
        // http://stackoverflow.com/questions/21837671/new-warning-in-android-4-4
        // Fix the non pre-multiplied exception for API 19+.
        // ギャラリーの画像はアルファチャンネル(プリマルチプライド)を設定されていない場合がある。
        // そのような画像をv19以降でキャンバスに設定するとエラーが発生する
        // そのため v19以降では明示的にsetPremultipliedを呼んであげる必要がある
        if ( android.os.Build.VERSION.SDK_INT >= 19 && !shadowImage32.isPremultiplied() )
        {
            shadowImage32.setPremultiplied( true );
        }
        Canvas c = new Canvas(shadowImage32);
        c.drawBitmap(bitmap, -offsetXY[0]-3, -offsetXY[1]-3, null);
        return shadowImage32;
    }

    private void updateNeighborViewsForId(long itemId) {
        idList.clear();
        int draggedPos = getPositionForID(itemId);
        for (int pos = getFirstVisiblePosition(); pos <= getLastVisiblePosition(); pos++) {
            if (draggedPos != pos && getAdapterInterface().canReorder(pos)) {
                idList.add(getId(pos));
            }
        }
    }

    /**
     * Retrieves the position in the grid corresponding to <code>itemId</code>
     */
    public int getPositionForID(long itemId) {
        View v = getViewForId(itemId);
        if (v == null) {
            return -1;
        } else {
            return getPositionForView(v);
        }
    }

    public View getViewForId(long itemId) {
        int firstVisiblePosition = getFirstVisiblePosition();
        ListAdapter adapter = 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;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                downX = (int) event.getX();
                downY = (int) event.getY();
                activePointerId = event.getPointerId(0);
                if (isEditMode && isEnabled()) {
                    layoutChildren();
                    int position = pointToPosition(downX, downY);
                    startDragAtPosition(position);
                } else if (!isEnabled()) {
                    return false;
                }

                break;

            case MotionEvent.ACTION_MOVE:
                if (activePointerId == INVALID_ID) {
                    break;
                }

                int pointerIndex = event.findPointerIndex(activePointerId);

                lastEventY = (int) event.getY(pointerIndex);
                lastEventX = (int) event.getX(pointerIndex);
                int deltaY = lastEventY - downY;
                int deltaX = lastEventX - downX;
                if (cellIsMobile) {
                    hoverCellCurrentBounds.offsetTo(hoverCellOriginalBounds.left + deltaX + totalOffsetX,
                            hoverCellOriginalBounds.top + deltaY + totalOffsetY);
                    hoverCell.setBounds(hoverCellCurrentBounds);
                    invalidate();
                    handleCellSwitch();
                    isMobileScrolling = false;
                    handleMobileCellScroll();
                    return false;
                }
                break;

            case MotionEvent.ACTION_UP:
                touchEventsEnded();

                if (undoSupportEnabled) {
                    if (currentModification != null && !currentModification.getTransitions().isEmpty()) {
                        modificationStack.push(currentModification);
                        currentModification = new DynamicGridModification();
                    }
                }

                if (hoverCell != null) {
                    if (dropListener != null) {
                        dropListener.onActionDrop();
                    }
                }
                break;

            case MotionEvent.ACTION_CANCEL:
                touchEventsCancelled();

                if (hoverCell != null) {
                    if (dropListener != null) {
                        dropListener.onActionDrop();
                    }
                }
                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 == activePointerId) {
                    touchEventsEnded();
                }
                break;

            default:
                break;
        }

        return super.onTouchEvent(event);
    }

    private void startDragAtPosition(int position) {
        totalOffsetY = 0;
        totalOffsetX = 0;
        int itemNum = position - getFirstVisiblePosition();
        View selectedView = getChildAt(itemNum);
        if (selectedView != null) {
            mobileItemId = getAdapter().getItemId(position);
            if (selectedItemBitmapCreationListener != null)
                selectedItemBitmapCreationListener.onPreSelectedItemBitmapCreation(selectedView, position, mobileItemId);
            hoverCell = getAndAddHoverView(selectedView);
            if (selectedItemBitmapCreationListener != null)
                selectedItemBitmapCreationListener.onPostSelectedItemBitmapCreation(selectedView, position, mobileItemId);
            selectedView.setVisibility(View.INVISIBLE);
            cellIsMobile = true;
            updateNeighborViewsForId(mobileItemId);
            if (dragListener != null) {
                dragListener.onDragStarted(position);
            }
        }
    }

    private void handleMobileCellScroll() {
        isMobileScrolling = handleMobileCellVerticalScroll(hoverCellCurrentBounds);
        isMobileScrolling = handleMobileCellHorizontalScroll(hoverCellCurrentBounds);
    }

    public boolean handleMobileCellVerticalScroll(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(-smoothScrollAmountAtEdge, 0);
            return true;
        }

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

        return false;
    }

    public boolean handleMobileCellHorizontalScroll(Rect r) {
        int offset = computeHorizontalScrollOffset();
        int width = getWidth();
        int extent = computeHorizontalScrollExtent();
        int range = computeHorizontalScrollRange();
        int hoverViewLeft = r.left;
        int hoverWidth = r.width();

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

        if (hoverViewLeft + hoverWidth >= width && (offset + extent) < range) {
            smoothScrollBy(smoothScrollAmountAtEdge, 0);
            return true;
        }

        return false;
    }

    @Override
    public void setAdapter(ListAdapter adapter) {
        super.setAdapter(adapter);
    }

    private void touchEventsEnded() {
        final View mobileView = getViewForId(mobileItemId);
        if (mobileView != null && (cellIsMobile || isWaitingForScrollFinish)) {
            cellIsMobile = false;
            isWaitingForScrollFinish = false;
            isMobileScrolling = false;
            activePointerId = INVALID_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 (scrollState != OnScrollListener.SCROLL_STATE_IDLE) {
                isWaitingForScrollFinish = true;
                return;
            }

            hoverCellCurrentBounds.offsetTo(mobileView.getLeft(), mobileView.getTop());

            if (Build.VERSION.SDK_INT > Build.VERSION_CODES.HONEYCOMB) {
                animateBounds(mobileView);
            } else {
                hoverCell.setBounds(hoverCellCurrentBounds);
                invalidate();
                reset(mobileView);
            }
        } else {
            touchEventsCancelled();
        }
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    private void animateBounds(final View mobileView) {
        TypeEvaluator<Rect> boundEvaluator = 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));
            }
        };


        ObjectAnimator hoverViewAnimator = ObjectAnimator.ofObject(hoverCell, "bounds",
                boundEvaluator, hoverCellCurrentBounds);
        hoverViewAnimator.addUpdateListener(valueAnimator -> invalidate());
        hoverViewAnimator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationStart(Animator animation) {
                hoverAnimation = true;
                updateEnableState();
            }

            @Override
            public void onAnimationEnd(Animator animation) {
                hoverAnimation = false;
                updateEnableState();
                reset(mobileView);
            }
        });
        hoverViewAnimator.start();
    }

    private void reset(View mobileView) {
        idList.clear();
        mobileItemId = INVALID_ID;
        mobileView.setVisibility(View.VISIBLE);
        hoverCell = null;
        //ugly fix for unclear disappearing items after reorder
        for (int i = 0; i < getLastVisiblePosition() - getFirstVisiblePosition(); i++) {
            View child = getChildAt(i);
            if (child != null) {
                child.setVisibility(View.VISIBLE);
            }
        }
        invalidate();
    }

    private void updateEnableState() {
        setEnabled(!hoverAnimation && !reorderAnimation);
    }

    private void touchEventsCancelled() {
        View mobileView = getViewForId(mobileItemId);
        if (cellIsMobile) {
            reset(mobileView);
        }
        cellIsMobile = false;
        isMobileScrolling = false;
        activePointerId = INVALID_ID;

    }

    private void handleCellSwitch() {
        final int deltaY = lastEventY - downY;
        final int deltaX = lastEventX - downX;
        final int deltaYTotal = hoverCellOriginalBounds.centerY() + totalOffsetY + deltaY;
        final int deltaXTotal = hoverCellOriginalBounds.centerX() + totalOffsetX + deltaX;
        mobileView = getViewForId(mobileItemId);
        View targetView = null;
        float vX = 0;
        float vY = 0;
        Point mobileColumnRowPair = getColumnAndRowForView(mobileView);
        for (Long id : idList) {
            View view = getViewForId(id);
            if (view != null) {
                Point targetColumnRowPair = getColumnAndRowForView(view);
                if ((aboveRight(targetColumnRowPair, mobileColumnRowPair)
                        && deltaYTotal < view.getBottom() && deltaXTotal > view.getLeft()
                        || aboveLeft(targetColumnRowPair, mobileColumnRowPair)
                        && deltaYTotal < view.getBottom() && deltaXTotal < view.getRight()
                        || belowRight(targetColumnRowPair, mobileColumnRowPair)
                        && deltaYTotal > view.getTop() && deltaXTotal > view.getLeft()
                        || belowLeft(targetColumnRowPair, mobileColumnRowPair)
                        && deltaYTotal > view.getTop() && deltaXTotal < view.getRight()
                        || above(targetColumnRowPair, mobileColumnRowPair)
                        && deltaYTotal < view.getBottom() - overlapIfSwitchStraightLine
                        || below(targetColumnRowPair, mobileColumnRowPair)
                        && deltaYTotal > view.getTop() + overlapIfSwitchStraightLine
                        || right(targetColumnRowPair, mobileColumnRowPair)
                        && deltaXTotal > view.getLeft() + overlapIfSwitchStraightLine
                        || left(targetColumnRowPair, mobileColumnRowPair)
                        && deltaXTotal < view.getRight() - overlapIfSwitchStraightLine)) {
                    float xDiff = Math.abs(DynamicGridUtils.getViewX(view) - DynamicGridUtils.getViewX(mobileView));
                    float yDiff = Math.abs(DynamicGridUtils.getViewY(view) - DynamicGridUtils.getViewY(mobileView));
                    if (xDiff >= vX && yDiff >= vY) {
                        vX = xDiff;
                        vY = yDiff;
                        targetView = view;
                    }
                }
            }
        }
        if (targetView != null) {
            final int originalPosition = getPositionForView(mobileView);
            int targetPosition = getPositionForView(targetView);
            // if targetPosition is not draggable then do nothing
            if(!selectedItemDraggableListener.isDraggable(targetPosition)) return;
            final DynamicGridAdapterInterface adapter = getAdapterInterface();
            if (targetPosition == INVALID_POSITION || !adapter.canReorder(originalPosition) || !adapter.canReorder(targetPosition)) {
                updateNeighborViewsForId(mobileItemId);
                return;
            }
            reorderElements(originalPosition, targetPosition);

            if (undoSupportEnabled) {
                currentModification.addTransition(originalPosition, targetPosition);
            }

            downY = lastEventY;
            downX = lastEventX;

            SwitchCellAnimator switchCellAnimator;

            if (!DeviceUtils.isAtLeastLollipop())   //below Android L
                switchCellAnimator = new KitKatSwitchCellAnimator(deltaX, deltaY);
            else                                //Android L
                switchCellAnimator = new LSwitchCellAnimator(deltaX, deltaY);

            updateNeighborViewsForId(mobileItemId);

            switchCellAnimator.animateSwitchCell(originalPosition, targetPosition);
        }
    }

    private interface SwitchCellAnimator {
        void animateSwitchCell(final int originalPosition, final int targetPosition);
    }

    /**
     * for versions KitKat and below.
     */
    private class KitKatSwitchCellAnimator implements SwitchCellAnimator {

        private int deltaY;
        private int deltaX;

        public KitKatSwitchCellAnimator(int deltaX, int deltaY) {
            this.deltaX = deltaX;
            this.deltaY = deltaY;
        }

        @Override
        public void animateSwitchCell(final int originalPosition, final int targetPosition) {
            assert mobileView != null;
            getViewTreeObserver().addOnPreDrawListener(new AnimateSwitchViewOnPreDrawListener(mobileView, originalPosition, targetPosition));
            mobileView = getViewForId(mobileItemId);
        }

        private class AnimateSwitchViewOnPreDrawListener implements ViewTreeObserver.OnPreDrawListener {

            private final View previousMobileView;
            private final int originalPosition;
            private final int targetPosition;

            AnimateSwitchViewOnPreDrawListener(final View previousMobileView, final int originalPosition, final int targetPosition) {
                this.previousMobileView = previousMobileView;
                this.originalPosition = originalPosition;
                this.targetPosition = targetPosition;
            }

            @Override
            public boolean onPreDraw() {
                getViewTreeObserver().removeOnPreDrawListener(this);

                totalOffsetY += deltaY;
                totalOffsetX += deltaX;

                animateReorder(originalPosition, targetPosition);

                previousMobileView.setVisibility(View.VISIBLE);

                if (mobileView != null) {
                    mobileView.setVisibility(View.INVISIBLE);
                }
                return true;
            }
        }
    }

    /**
     *  for versions L and above.
     */
    private class LSwitchCellAnimator implements SwitchCellAnimator {

        private int deltaY;
        private int deltaX;

        public LSwitchCellAnimator(int deltaX, int deltaY) {
            this.deltaX = deltaX;
            this.deltaY = deltaY;
        }

        @Override
        public void animateSwitchCell(final int originalPosition, final int targetPosition) {
            getViewTreeObserver().addOnPreDrawListener(new AnimateSwitchViewOnPreDrawListener(originalPosition, targetPosition));
        }

        private class AnimateSwitchViewOnPreDrawListener implements ViewTreeObserver.OnPreDrawListener {
            private final int originalPosition;
            private final int targetPosition;

            AnimateSwitchViewOnPreDrawListener(final int originalPosition, final int targetPosition) {
                this.originalPosition = originalPosition;
                this.targetPosition = targetPosition;
            }

            @Override
            public boolean onPreDraw() {
                getViewTreeObserver().removeOnPreDrawListener(this);

                totalOffsetY += deltaY;
                totalOffsetX += deltaX;

                animateReorder(originalPosition, targetPosition);

                assert mobileView != null;
                mobileView.setVisibility(View.VISIBLE);
                mobileView = getViewForId(mobileItemId);
                assert mobileView != null;
                mobileView.setVisibility(View.INVISIBLE);
                return true;
            }
        }
    }

    private boolean belowLeft(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y > mobileColumnRowPair.y && targetColumnRowPair.x < mobileColumnRowPair.x;
    }

    private boolean belowRight(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y > mobileColumnRowPair.y && targetColumnRowPair.x > mobileColumnRowPair.x;
    }

    private boolean aboveLeft(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y < mobileColumnRowPair.y && targetColumnRowPair.x < mobileColumnRowPair.x;
    }

    private boolean aboveRight(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y < mobileColumnRowPair.y && targetColumnRowPair.x > mobileColumnRowPair.x;
    }

    private boolean above(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y < mobileColumnRowPair.y && targetColumnRowPair.x == mobileColumnRowPair.x;
    }

    private boolean below(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y > mobileColumnRowPair.y && targetColumnRowPair.x == mobileColumnRowPair.x;
    }

    private boolean right(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y == mobileColumnRowPair.y && targetColumnRowPair.x > mobileColumnRowPair.x;
    }

    private boolean left(Point targetColumnRowPair, Point mobileColumnRowPair) {
        return targetColumnRowPair.y == mobileColumnRowPair.y && targetColumnRowPair.x < mobileColumnRowPair.x;
    }

    private Point getColumnAndRowForView(View view) {
        int pos = getPositionForView(view);
        int columns = getColumnCount();
        int column = pos % columns;
        int row = pos / columns;
        return new Point(column, row);
    }

    private long getId(int position) {
        return getAdapter().getItemId(position);
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    private void animateReorder(final int oldPosition, final int newPosition) {
        boolean isForward = newPosition > oldPosition;
        List<Animator> resultList = new LinkedList<>();
        if (isForward) {
            for (int pos = Math.min(oldPosition, newPosition); pos < Math.max(oldPosition, newPosition); pos++) {
                View view = getViewForId(getId(pos));
                if ((pos + 1) % getColumnCount() == 0) {
                    resultList.add(createTranslationAnimations(view, -view.getWidth() * (getColumnCount() - 1), 0,
                            view.getHeight(), 0));
                } else {
                    resultList.add(createTranslationAnimations(view, view.getWidth(), 0, 0, 0));
                }
            }
        } else {
            for (int pos = Math.max(oldPosition, newPosition); pos > Math.min(oldPosition, newPosition); pos--) {
                View view = getViewForId(getId(pos));
                if ((pos + getColumnCount()) % getColumnCount() == 0) {
                    resultList.add(createTranslationAnimations(view, view.getWidth() * (getColumnCount() - 1), 0,
                            -view.getHeight(), 0));
                } else {
                    resultList.add(createTranslationAnimations(view, -view.getWidth(), 0, 0, 0));
                }
            }
        }

        AnimatorSet resultSet = new AnimatorSet();
        resultSet.playTogether(resultList);
        resultSet.setDuration(MOVE_DURATION);
        resultSet.setInterpolator(new AccelerateDecelerateInterpolator());
        resultSet.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationStart(Animator animation) {
                reorderAnimation = true;
                updateEnableState();
            }

            @Override
            public void onAnimationEnd(Animator animation) {
                reorderAnimation = false;
                updateEnableState();
            }
        });
        resultSet.start();
    }


    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    private AnimatorSet createTranslationAnimations(View view, float startX, float endX, float startY, float endY) {
        ObjectAnimator animX = ObjectAnimator.ofFloat(view, "translationX", startX, endX);
        ObjectAnimator animY = ObjectAnimator.ofFloat(view, "translationY", startY, endY);
        AnimatorSet animSetXY = new AnimatorSet();
        animSetXY.playTogether(animX, animY);
        return animSetXY;
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        if (hoverCell != null) {
            hoverCell.draw(canvas);
        }
    }


    public interface OnDropListener {
        void onActionDrop();
    }

    public interface OnDragListener {

        public void onDragStarted(int position);

        public void onDragPositionsChanged(int oldPosition, int newPosition);
    }

    public interface OnEditModeChangeListener {
        public void onEditModeChanged(boolean inEditMode);
    }

    public interface OnSelectedItemBitmapCreationListener {
        public void onPreSelectedItemBitmapCreation(View selectedView, int position, long itemId);

        public void onPostSelectedItemBitmapCreation(View selectedView, int position, long itemId);
    }

    public interface OnSelectedItemDraggableListener {
        boolean isDraggable(int position);
    }


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

        private int previousFirstVisibleItem = -1;
        private int previousVisibleItemCount = -1;
        private int currentFirstVisibleItem;
        private int currentVisibleItemCount;
        private int currentScrollState;

        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
                             int totalItemCount) {
            currentFirstVisibleItem = firstVisibleItem;
            currentVisibleItemCount = visibleItemCount;

            previousFirstVisibleItem = (previousFirstVisibleItem == -1) ? currentFirstVisibleItem
                    : previousFirstVisibleItem;
            previousVisibleItemCount = (previousVisibleItemCount == -1) ? currentVisibleItemCount
                    : previousVisibleItemCount;

            checkAndHandleFirstVisibleCellChange();
            checkAndHandleLastVisibleCellChange();

            previousFirstVisibleItem = currentFirstVisibleItem;
            previousVisibleItemCount = currentVisibleItemCount;

            if (userScrollListener != null) {
                userScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
            }
        }

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
            currentScrollState = scrollState;
            DynamicGridView.this.scrollState = scrollState;
            isScrollCompleted();
            if (userScrollListener != null) {
                userScrollListener.onScrollStateChanged(view, scrollState);
            }
        }

        /**
         * This method is in charge of invoking 1 of 2 actions. Firstly, if the gridview
         * is in a state of scrolling invoked by the hover cell being outside the bounds
         * of the gridview, 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 gridview has entered an idle scroll
         * state.
         */
        private void isScrollCompleted() {
            if (currentVisibleItemCount > 0 && currentScrollState == SCROLL_STATE_IDLE) {
                if (cellIsMobile && isMobileScrolling) {
                    handleMobileCellScroll();
                } else if (isWaitingForScrollFinish) {
                    touchEventsEnded();
                }
            }
        }

        /**
         * Determines if the gridview 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 (currentFirstVisibleItem != previousFirstVisibleItem) {
                if (cellIsMobile && mobileItemId != INVALID_ID) {
                    updateNeighborViewsForId(mobileItemId);
                    handleCellSwitch();
                }
            }
        }

        /**
         * Determines if the gridview 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 = currentFirstVisibleItem + currentVisibleItemCount;
            int previousLastVisibleItem = previousFirstVisibleItem + previousVisibleItemCount;
            if (currentLastVisibleItem != previousLastVisibleItem) {
                if (cellIsMobile && mobileItemId != INVALID_ID) {
                    updateNeighborViewsForId(mobileItemId);
                    handleCellSwitch();
                }
            }
        }
    };

    private static class DynamicGridModification {

        private List<Pair<Integer, Integer>> transitions;

        DynamicGridModification() {
            super();
            this.transitions = new Stack<>();
        }

        public boolean hasTransitions() {
            return !transitions.isEmpty();
        }

        public void addTransition(int oldPosition, int newPosition) {
            transitions.add(new Pair<>(oldPosition, newPosition));
        }

        public List<Pair<Integer, Integer>> getTransitions() {
            Collections.reverse(transitions);
            return transitions;
        }
    }
}