Created
October 26, 2014 05:37
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Calculate list scroll distance without any modification to ListView and ListAdapter. great for QuickReturn pattern
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| package org.mariotaku.twidere.util; | |
| import android.view.View; | |
| import android.widget.AbsListView; | |
| import android.widget.AbsListView.OnScrollListener; | |
| /** | |
| * Created by mariotaku on 14/10/22. | |
| */ | |
| public class ListScrollDistanceCalculator implements OnScrollListener { | |
| private ScrollDistanceListener mScrollDistanceListener; | |
| private boolean mListScrollStarted; | |
| private int mFirstVisibleItem; | |
| private int mFirstVisibleHeight; | |
| private int mFirstVisibleTop, mFirstVisibleBottom; | |
| private int mTotalScrollDistance; | |
| @Override | |
| public void onScrollStateChanged(AbsListView view, int scrollState) { | |
| if (view.getCount() == 0) return; | |
| switch (scrollState) { | |
| case SCROLL_STATE_IDLE: { | |
| mListScrollStarted = false; | |
| break; | |
| } | |
| case SCROLL_STATE_TOUCH_SCROLL: { | |
| final View firstChild = view.getChildAt(0); | |
| mFirstVisibleItem = view.getFirstVisiblePosition(); | |
| mFirstVisibleTop = firstChild.getTop(); | |
| mFirstVisibleBottom = firstChild.getBottom(); | |
| mFirstVisibleHeight = firstChild.getHeight(); | |
| mListScrollStarted = true; | |
| mTotalScrollDistance = 0; | |
| break; | |
| } | |
| } | |
| } | |
| public int getTotalScrollDistance() { | |
| return mTotalScrollDistance; | |
| } | |
| @Override | |
| public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { | |
| if (totalItemCount == 0 || !mListScrollStarted) return; | |
| final View firstChild = view.getChildAt(0); | |
| final int firstVisibleTop = firstChild.getTop(), firstVisibleBottom = firstChild.getBottom(); | |
| final int firstVisibleHeight = firstChild.getHeight(); | |
| final int delta; | |
| if (firstVisibleItem > mFirstVisibleItem) { | |
| mFirstVisibleTop += mFirstVisibleHeight; | |
| delta = firstVisibleTop - mFirstVisibleTop; | |
| } else if (firstVisibleItem < mFirstVisibleItem) { | |
| mFirstVisibleBottom -= mFirstVisibleHeight; | |
| delta = firstVisibleBottom - mFirstVisibleBottom; | |
| } else { | |
| delta = firstVisibleBottom - mFirstVisibleBottom; | |
| } | |
| mTotalScrollDistance += delta; | |
| if (mScrollDistanceListener != null) { | |
| mScrollDistanceListener.onScrollDistanceChanged(delta, mTotalScrollDistance); | |
| } | |
| mFirstVisibleTop = firstVisibleTop; | |
| mFirstVisibleBottom = firstVisibleBottom; | |
| mFirstVisibleHeight = firstVisibleHeight; | |
| mFirstVisibleItem = firstVisibleItem; | |
| } | |
| public void setScrollDistanceListener(ScrollDistanceListener listener) { | |
| mScrollDistanceListener = listener; | |
| } | |
| public static interface ScrollDistanceListener { | |
| void onScrollDistanceChanged(int delta, int total); | |
| } | |
| } |
when fling faster, the delta will be wrong
that is just great!
when fling faster, the delta will be wrong
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thanks!