Android Open Source - HydraListAndroid Dragable List View Delegate

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License

The source code is released under:

Apache License

Java Source Code

/*
 * Copyright (C) 2013 The Android Open Source Project
 * //from   ww  w  . j ava 2 s .co m
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.fada21.android.hydralist.dragable;

import static com.fada21.android.hydralist.dragable.DragableConsts.INVALID_POINTER_ID;
import static com.fada21.android.hydralist.dragable.DragableConsts.INVALID_POSITION;
import static com.fada21.android.hydralist.dragable.DragableConsts.MOVE_DURATION;
import static com.fada21.android.hydralist.dragable.DragableConsts.SMOOTH_SCROLL_AMOUNT_AT_EDGE;
import static com.fada21.android.hydralist.util.HydraListConsts.INVALID_ID;
import static com.fada21.android.hydralist.util.HydraListConsts.UNSET;
import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ObjectAnimator;
import android.animation.TypeEvaluator;
import android.animation.ValueAnimator;
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.HeaderViewListAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;

import com.fada21.android.hydralist.HydraListAdapter;
import com.fada21.android.hydralist.dragable.interfaces.DragableListItem;
import com.fada21.android.hydralist.dragable.interfaces.OnItemMovedListener;
import com.fada21.android.hydralist.dragable.interfaces.Swappable;
import com.fada21.android.hydralist.util.PublicListView;

/**
 * The dragable listview is an extension of listview that supports cell dragging and swapping.
 * 
 * This layout is in charge of positioning the hover cell in the correct location on the screen in response to user touch events. It uses the position of the
 * hover cell to determine when two cells should be swapped. If two cells should be swapped, all the corresponding data set and layout changes are handled here.
 * 
 * If no cell is selected, all the touch events are passed down to the listview and behave normally. If one of the items in the listview experiences a long
 * press event, the contents of its current visible state are captured as a bitmap and its visibility is set to INVISIBLE. A hover cell is then created and
 * added to this layout as an overlaying BitmapDrawable above the listview. Once the hover cell is translated some distance to signify an item swap, a data set
 * change accompanied by animation takes place. When the user releases the hover cell, it animates into its corresponding position in the listview.
 * 
 * When the hover cell is either above or below the bounds of the listview, this listview also scrolls on its own so as to reveal additional content.
 */
public class DragableListViewDelegate {

  private int mOriginalTranscriptMode;

  public interface OnHoverCellListener {
    public Drawable onHoverCellCreated(Drawable hoverCellDrawable);
  }

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

  private Drawable mHoverCell;
  private Rect mHoverCellCurrentBounds;
  private Rect mHoverCellOriginalBounds;

  private int mActivePointerId = INVALID_POINTER_ID;

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

  private boolean mIsParentHorizontalScrollContainer;
  private int mDragableTouchResId;
  private boolean mIsTouchedDragableView;
  private int mSlop;

  private OnHoverCellListener mOnHoverCellListener;

  private OnItemMovedListener mOnItemMovedListener;
  private int mLastMovedToIndex;

  private final PublicListView nlv;

  public DragableListViewDelegate(PublicListView nlv) {
    this.nlv = nlv;
    init(nlv.getContext());
  }

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

  private ListAdapter getAdapter() {
    return nlv.getAdapter();
  }

  /**
   * Listens for long clicks on any items in the listview. When a cell has been selected, the hover cell is created and set up.
   */
  private AdapterView.OnItemLongClickListener mOnItemLongClickListener = initOnItemLongClickListener();

  private AdapterView.OnItemLongClickListener initOnItemLongClickListener() {
    return new AdapterView.OnItemLongClickListener() {
      public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {

        if (mDragableTouchResId == UNSET) {
          mIsTouchedDragableView = true;
          mCellIsMobile = makeCellMobile();
          return mCellIsMobile;
        }
        return false;
      }

    };
  }

  private boolean makeCellMobile() {
    int position = nlv.pointToPosition(mDownX, mDownY);
    if (!isDragable(position)) {
      return false;
    }
    
    int itemNum = position - nlv.getFirstVisiblePosition();
    View selectedView = nlv.getChildAt(itemNum);
    if (selectedView == null || position < nlv.getHeaderViewsCount() || position >= getAdapter().getCount() - nlv.getHeaderViewsCount()) {
      return false;
    }

    mOriginalTranscriptMode = nlv.getTranscriptMode();
    nlv.setTranscriptMode(ListView.TRANSCRIPT_MODE_NORMAL);

    mTotalOffset = 0;

    mMobileItemId = getAdapter().getItemId(position);
    mHoverCell = getAndAddHoverView(selectedView);
    if (mOnHoverCellListener != null) {
      mHoverCell = mOnHoverCellListener.onHoverCellCreated(mHoverCell);
    }
    selectedView.setVisibility(View.INVISIBLE);

    nlv.getParent().requestDisallowInterceptTouchEvent(true);

    updateNeighborViewsForId(mMobileItemId);
    
    return true;
  }
  
  private boolean isDragable(int position) {
    boolean isDragable = true;
    try {
      DragableListItem item = (DragableListItem) getAdapter().getItem(position);
      isDragable = item.isDragable();
    } catch (ClassCastException cce) {
      // assume that all items should be dragable
    }
    return isDragable;
  }

  /**
   * 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);

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

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

    drawable.setBounds(mHoverCellCurrentBounds);

    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;
  }

  /**
   * 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);
    ListAdapter adapter = getAdapter();
    if (!adapter.hasStableIds()) {
      throw new IllegalStateException(
          "Adapter doesn't have stable ids! Make sure your adapter has stable ids, and override hasStableIds() to return true.");
    }

    mAboveItemId = position - 1 >= 0 ? adapter.getItemId(position - 1) : ListView.INVALID_ROW_ID;
    mBelowItemId = position + 1 < adapter.getCount() ? adapter.getItemId(position + 1) : ListView.INVALID_ROW_ID;
  }

  /**
   * Retrieves the view in the list corresponding to itemId
   */
  private View getViewForId(long itemId) {
    int firstVisiblePosition = nlv.getFirstVisiblePosition();
    ListAdapter adapter = getAdapter();
    if (!adapter.hasStableIds()) {
      throw new IllegalStateException(
          "Adapter doesn't have stable ids! Make sure your adapter has stable ids, and override hasStableIds() to return true.");
    }

    for (int i = 0; i < nlv.getChildCount(); i++) {
      View v = nlv.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
   */
  private int getPositionForId(long itemId) {
    View v = getViewForId(itemId);
    if (v == null) {
      return -1;
    } else {
      return nlv.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 items whenever the listview is redrawn.
   */
  public void dispatchDraw(Canvas canvas) {
    if (mHoverCell != null) {
      mHoverCell.draw(canvas);
    }
  }

  public void setOnHoverCellListener(OnHoverCellListener onHoverCellListener) {
    mOnHoverCellListener = onHoverCellListener;
  }

  private Rect getChildViewRect(View parentView, View childView) {
    final Rect childRect = new Rect(childView.getLeft(), childView.getTop(), childView.getRight(), childView.getBottom());
    if (parentView == childView) {
      return childRect;
    }

    ViewGroup parent;
    while ((parent = (ViewGroup) childView.getParent()) != parentView) {
      childRect.offset(parent.getLeft(), parent.getTop());
      childView = parent;
    }

    return childRect;
  }

  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);

      mIsTouchedDragableView = false;
      if (mDragableTouchResId != UNSET) {
        mIsParentHorizontalScrollContainer = false;

        int position = nlv.pointToPosition(mDownX, mDownY);
        int childNum = (position != ListView.INVALID_POSITION) ? position - nlv.getFirstVisiblePosition() : -1;
        View itemView = (childNum >= 0) ? nlv.getChildAt(childNum) : null;
        View childView = (itemView != null) ? itemView.findViewById(mDragableTouchResId) : null;
        if (childView != null) {
          final Rect childRect = getChildViewRect(nlv, childView);
          if (childRect.contains(mDownX, mDownY)) {
            mIsTouchedDragableView = true;
            nlv.getParent().requestDisallowInterceptTouchEvent(true);
          }
        }
      }

      if (mIsParentHorizontalScrollContainer) {
        // Do it now and don't wait until the user moves more than the slop factor.
        nlv.getParent().requestDisallowInterceptTouchEvent(true);
      }
      break;
    case MotionEvent.ACTION_MOVE:
      if (mActivePointerId == INVALID_POINTER_ID) {
        break;
      }

      int pointerIndex = event.findPointerIndex(mActivePointerId);

      mLastEventX = (int) event.getX(pointerIndex);
      mLastEventY = (int) event.getY(pointerIndex);
      int deltaX = mLastEventX - mDownX;
      int deltaY = mLastEventY - mDownY;

      if (!mCellIsMobile && mIsTouchedDragableView) {
        if (Math.abs(deltaY) > mSlop && Math.abs(deltaY) > Math.abs(deltaX)) {
          mCellIsMobile = makeCellMobile();
          mIsTouchedDragableView = mCellIsMobile;
        }
      }

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

        handleCellSwitch();

        mIsMobileScrolling = false;
        handleMobileCellScroll();
      }
      break;
    case MotionEvent.ACTION_UP:
      mIsTouchedDragableView = false;
      touchEventsEnded();
      break;
    case MotionEvent.ACTION_CANCEL:
      mIsTouchedDragableView = false;
      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) {
        mIsTouchedDragableView = false;
        touchEventsEnded();
      }
      break;
    default:
      break;
    }

    if (mCellIsMobile) {
      return true;
    } else {
      return false;
    }
  }

  /**
   * 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 = mobileView !=null ? nlv.getPositionForView(mobileView) : INVALID_POSITION; 

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

      int positionForView = nlv.getPositionForView(switchView);
      if (positionForView < nlv.getHeaderViewsCount()) {
        return;
      }

      BaseAdapter adapter;
      if (getAdapter() instanceof HeaderViewListAdapter) {
        adapter = (BaseAdapter) ((HeaderViewListAdapter) getAdapter()).getWrappedAdapter();
      } else {
        adapter = (BaseAdapter) getAdapter();
      }
      swapElements(originalItem, positionForView);

      mDownY = mLastEventY;
      mDownX = mLastEventX;

      final int switchViewStartTop = switchView.getTop();

      mobileView.setVisibility(View.VISIBLE);

      updateNeighborViewsForId(mMobileItemId);

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

          View switchView = getViewForId(switchItemId);

          mTotalOffset += deltaY;

          int switchViewNewTop = switchView.getTop();
          int delta = switchViewStartTop - switchViewNewTop;

          switchView.setTranslationY(delta);

          ObjectAnimator animator = ObjectAnimator.ofFloat(switchView, "translationY", 0);
          animator.setDuration(MOVE_DURATION);
          animator.start();
          
          return true;
        }
      });
            observer.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {

                @SuppressWarnings("deprecation")
                @SuppressLint("NewApi")
                public void onGlobalLayout() {
                    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) {
                        observer.removeGlobalOnLayoutListener(this);
                    } else {
                        observer.removeOnGlobalLayoutListener(this);
                    }
                    getViewForId(mMobileItemId).setVisibility(View.INVISIBLE);
                }
            });
    }
  }

  private void swapElements(int indexOne, int indexTwo) {
    HydraListAdapter<?> hlva = (HydraListAdapter<?>) getAdapter();
    Swappable dataProvider = (Swappable) hlva.getDataProvider();
    dataProvider.swap(indexOne, indexTwo);
    hlva.notifyDataSetChanged();
  }

  /**
   * 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;

      /* Restore the transcript mode */
      nlv.setTranscriptMode(mOriginalTranscriptMode);

      // 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) {
          nlv.invalidate();
        }
      });
      hoverViewAnimator.addListener(new AnimatorListenerAdapter() {
        @Override
        public void onAnimationStart(Animator animation) {
          nlv.setEnabled(false);
        }

        @Override
        public void onAnimationEnd(Animator animation) {
                    final long toReportAboveId = mAboveItemId;
                    final long toReportMovedId = mMobileItemId;
                    final long toReportBelowId = mBelowItemId;
          mAboveItemId = INVALID_ID;
          mMobileItemId = INVALID_ID;
          mBelowItemId = INVALID_ID;
          mobileView.setVisibility(View.VISIBLE);
          mHoverCell = null;
          nlv.setEnabled(true);
          nlv.invalidate();
          if (mOnItemMovedListener != null) {
                        mOnItemMovedListener.onItemMoved(toReportMovedId, toReportAboveId, toReportBelowId);
                    }
        }
      });
      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(View.VISIBLE);
      mHoverCell = null;
      nlv.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 items.
   */
  private boolean handleMobileCellScroll(Rect r) {
    int offset = nlv.computeVerticalScrollOffset();
    int height = nlv.getHeight();
    int extent = nlv.computeVerticalScrollExtent();
    int range = nlv.computeVerticalScrollRange();
    int hoverViewTop = r.top;
    int hoverHeight = r.height();

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

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

    return false;
  }

  public void setIsParentHorizontalScrollContainer(boolean isParentHorizontalScrollContainer) {
    mIsParentHorizontalScrollContainer = (mDragableTouchResId == UNSET) && isParentHorizontalScrollContainer;
  }

  public boolean isParentHorizontalScrollContainer() {
    return mIsParentHorizontalScrollContainer;
  }

  public void setDragableTouchResId(int resId) {
    mDragableTouchResId = resId;
    if (resId != UNSET) {
      setIsParentHorizontalScrollContainer(false);
    }
  }

  /**
   * 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();
        }
      }
    }
  };

  /**
   * Set listener to be notified when an item is dropped.
   */
  public void setOnItemMovedListener(OnItemMovedListener onItemMovedListener) {
    this.mOnItemMovedListener = onItemMovedListener;
  }
}

Java Source Code List

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