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simple implementation of quick return pattern for android listview
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public class QuickReturn implements AbsListView.OnScrollListener { | |
public static QuickReturn apply(ListView listView, View targetView){ | |
return new QuickReturn(listView, targetView); | |
} | |
private final ListView mListView; | |
private final View mTargetView; | |
private AbsListView.OnScrollListener mOnScrollListener; | |
private int mLastFirstVisibleItem; | |
private int mLastTop; | |
private int mLastHeight; | |
private QuickReturn(ListView listView, View targetView) { | |
mListView = listView; | |
mTargetView = targetView; | |
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { | |
mListView.setOnScrollListener(this); | |
} | |
} | |
public void withOnScrollListener(AbsListView.OnScrollListener onScrollListener) { | |
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { | |
mOnScrollListener = onScrollListener; | |
} else { | |
mListView.setOnScrollListener(onScrollListener); | |
} | |
} | |
@Override | |
public void onScrollStateChanged(AbsListView view, int scrollState) { | |
if (mOnScrollListener != null) { | |
mOnScrollListener.onScrollStateChanged(view, scrollState); | |
} | |
} | |
@Override | |
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { | |
if (mOnScrollListener != null) { | |
mOnScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount); | |
} | |
View v = mListView.getChildAt(0); | |
int top = (v == null) ? 0 : v.getTop(); | |
int height = (v == null) ? 0 : v.getHeight(); | |
if (firstVisibleItem == mLastFirstVisibleItem) { | |
translateBy(top - mLastTop); | |
} else { | |
if (firstVisibleItem > mLastFirstVisibleItem) { | |
translateBy(-mLastHeight - mLastTop + top); | |
} else { | |
translateBy(height - mLastTop + top); | |
} | |
} | |
mLastFirstVisibleItem = firstVisibleItem; | |
mLastTop = top; | |
mLastHeight = height; | |
} | |
@TargetApi(Build.VERSION_CODES.HONEYCOMB) | |
private void translateBy(int offsetY) { | |
int newTranslation = (int) mTargetView.getTranslationY() + offsetY; | |
if (newTranslation < -mTargetView.getHeight()) { | |
mTargetView.setTranslationY(-mTargetView.getHeight()); | |
} else if (newTranslation > 0) { | |
mTargetView.setTranslationY(0); | |
} else { | |
mTargetView.setTranslationY(newTranslation); | |
} | |
} | |
} |
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QuickReturn.apply(mListView, mTargetView).withOnScrollListener(this); |
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