android.support.v7.util.BatchingListUpdateCallback Maven / Gradle / Ivy
package android.support.v7.util;
/**
* Wraps a {@link ListUpdateCallback} callback and batches operations that can be merged.
*
* For instance, when 2 add operations comes that adds 2 consecutive elements,
* BatchingListUpdateCallback merges them and calls the wrapped callback only once.
*
* This is a general purpose class and is also used by
* {@link android.support.v7.util.DiffUtil.DiffResult DiffResult} and
* {@link SortedList} to minimize the number of updates that are dispatched.
*
* If you use this class to batch updates, you must call {@link #dispatchLastEvent()} when the
* stream of update events drain.
*/
public class BatchingListUpdateCallback implements ListUpdateCallback {
private static final int TYPE_NONE = 0;
private static final int TYPE_ADD = 1;
private static final int TYPE_REMOVE = 2;
private static final int TYPE_CHANGE = 3;
final ListUpdateCallback mWrapped;
int mLastEventType = TYPE_NONE;
int mLastEventPosition = -1;
int mLastEventCount = -1;
Object mLastEventPayload = null;
public BatchingListUpdateCallback(ListUpdateCallback callback) {
mWrapped = callback;
}
/**
* BatchingListUpdateCallback holds onto the last event to see if it can be merged with the
* next one. When stream of events finish, you should call this method to dispatch the last
* event.
*/
public void dispatchLastEvent() {
if (mLastEventType == TYPE_NONE) {
return;
}
switch (mLastEventType) {
case TYPE_ADD:
mWrapped.onInserted(mLastEventPosition, mLastEventCount);
break;
case TYPE_REMOVE:
mWrapped.onRemoved(mLastEventPosition, mLastEventCount);
break;
case TYPE_CHANGE:
mWrapped.onChanged(mLastEventPosition, mLastEventCount, mLastEventPayload);
break;
}
mLastEventPayload = null;
mLastEventType = TYPE_NONE;
}
@Override
public void onInserted(int position, int count) {
if (mLastEventType == TYPE_ADD && position >= mLastEventPosition
&& position <= mLastEventPosition + mLastEventCount) {
mLastEventCount += count;
mLastEventPosition = Math.min(position, mLastEventPosition);
return;
}
dispatchLastEvent();
mLastEventPosition = position;
mLastEventCount = count;
mLastEventType = TYPE_ADD;
}
@Override
public void onRemoved(int position, int count) {
if (mLastEventType == TYPE_REMOVE && mLastEventPosition >= position &&
mLastEventPosition <= position + count) {
mLastEventCount += count;
mLastEventPosition = position;
return;
}
dispatchLastEvent();
mLastEventPosition = position;
mLastEventCount = count;
mLastEventType = TYPE_REMOVE;
}
@Override
public void onMoved(int fromPosition, int toPosition) {
dispatchLastEvent(); // moves are not merged
mWrapped.onMoved(fromPosition, toPosition);
}
@Override
public void onChanged(int position, int count, Object payload) {
if (mLastEventType == TYPE_CHANGE &&
!(position > mLastEventPosition + mLastEventCount
|| position + count < mLastEventPosition || mLastEventPayload != payload)) {
// take potential overlap into account
int previousEnd = mLastEventPosition + mLastEventCount;
mLastEventPosition = Math.min(position, mLastEventPosition);
mLastEventCount = Math.max(previousEnd, position + count) - mLastEventPosition;
return;
}
dispatchLastEvent();
mLastEventPosition = position;
mLastEventCount = count;
mLastEventPayload = payload;
mLastEventType = TYPE_CHANGE;
}
}