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The source code is released under:
GNU Lesser General Public License
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/* * Copyright (C) 2007 The Android Open Source Project */* ww w. j a v a2 s. c om*/ * 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 org.yammp.util; import android.database.AbstractCursor; import android.database.Cursor; import android.database.DataSetObserver; import android.util.Log; /** * A variant of MergeCursor that sorts the cursors being merged. If decent * performance is ever obtained, it can be put back under android.database. */ public class SortCursor extends AbstractCursor { private static final String TAG = "SortCursor"; private Cursor mCursor; // updated in onMove private Cursor[] mCursors; private int[] mSortColumns; private final int ROWCACHESIZE = 64; private int mRowNumCache[] = new int[ROWCACHESIZE]; private int mCursorCache[] = new int[ROWCACHESIZE]; private int mCurRowNumCache[][]; private int mLastCacheHit = -1; private DataSetObserver mObserver = new DataSetObserver() { @Override public void onChanged() { // Reset our position so the optimizations in move-related code // don't screw us over mPos = -1; } @Override public void onInvalidated() { mPos = -1; } }; public SortCursor(Cursor[] cursors, String sortcolumn) { mCursors = cursors; int length = mCursors.length; mSortColumns = new int[length]; for (int i = 0; i < length; i++) { if (mCursors[i] == null) { continue; } // Register ourself as a data set observer mCursors[i].registerDataSetObserver(mObserver); mCursors[i].moveToFirst(); // We don't catch the exception mSortColumns[i] = mCursors[i].getColumnIndexOrThrow(sortcolumn); } mCursor = null; String smallest = ""; for (int j = 0; j < length; j++) { if (mCursors[j] == null || mCursors[j].isAfterLast()) { continue; } String current = mCursors[j].getString(mSortColumns[j]); if (mCursor == null || current.compareToIgnoreCase(smallest) < 0) { smallest = current; mCursor = mCursors[j]; } } for (int i = mRowNumCache.length - 1; i >= 0; i--) { mRowNumCache[i] = -2; } mCurRowNumCache = new int[ROWCACHESIZE][length]; } @Override public void close() { int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] == null) { continue; } mCursors[i].close(); } } @Override public void deactivate() { int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] == null) { continue; } mCursors[i].deactivate(); } } @Override public byte[] getBlob(int column) { return mCursor.getBlob(column); } @Override public String[] getColumnNames() { if (mCursor != null) return mCursor.getColumnNames(); else { // All of the cursors may be empty, but they can still return // this information. int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] != null) return mCursors[i].getColumnNames(); } throw new IllegalStateException("No cursor that can return names"); } } @Override public int getCount() { int count = 0; int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] != null) { count += mCursors[i].getCount(); } } return count; } @Override public double getDouble(int column) { return mCursor.getDouble(column); } @Override public float getFloat(int column) { return mCursor.getFloat(column); } @Override public int getInt(int column) { return mCursor.getInt(column); } @Override public long getLong(int column) { return mCursor.getLong(column); } @Override public short getShort(int column) { return mCursor.getShort(column); } @Override public String getString(int column) { return mCursor.getString(column); } @Override public boolean isNull(int column) { return mCursor.isNull(column); } @Override public boolean onMove(int oldPosition, int newPosition) { if (oldPosition == newPosition) return true; /* * Find the right cursor Because the client of this cursor (the * listadapter/view) tends to jump around in the cursor somewhat, a * simple cache strategy is used to avoid having to search all cursors * from the start. TODO: investigate strategies for optimizing random * access and reverse-order access. */ int cache_entry = newPosition % ROWCACHESIZE; if (mRowNumCache[cache_entry] == newPosition) { int which = mCursorCache[cache_entry]; mCursor = mCursors[which]; if (mCursor == null) { Log.w(TAG, "onMove: cache results in a null cursor."); return false; } mCursor.moveToPosition(mCurRowNumCache[cache_entry][which]); mLastCacheHit = cache_entry; return true; } mCursor = null; int length = mCursors.length; if (mLastCacheHit >= 0) { for (int i = 0; i < length; i++) { if (mCursors[i] == null) { continue; } mCursors[i].moveToPosition(mCurRowNumCache[mLastCacheHit][i]); } } if (newPosition < oldPosition || oldPosition == -1) { for (int i = 0; i < length; i++) { if (mCursors[i] == null) { continue; } mCursors[i].moveToFirst(); } oldPosition = 0; } if (oldPosition < 0) { oldPosition = 0; } // search forward to the new position int smallestIdx = -1; for (int i = oldPosition; i <= newPosition; i++) { String smallest = ""; smallestIdx = -1; for (int j = 0; j < length; j++) { if (mCursors[j] == null || mCursors[j].isAfterLast()) { continue; } String current = mCursors[j].getString(mSortColumns[j]); if (smallestIdx < 0 || current.compareToIgnoreCase(smallest) < 0) { smallest = current; smallestIdx = j; } } if (i == newPosition) { break; } if (mCursors[smallestIdx] != null) { mCursors[smallestIdx].moveToNext(); } } mCursor = mCursors[smallestIdx]; mRowNumCache[cache_entry] = newPosition; mCursorCache[cache_entry] = smallestIdx; for (int i = 0; i < length; i++) { if (mCursors[i] != null) { mCurRowNumCache[cache_entry][i] = mCursors[i].getPosition(); } } mLastCacheHit = -1; return true; } @Override public void registerDataSetObserver(DataSetObserver observer) { int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] != null) { mCursors[i].registerDataSetObserver(observer); } } } @Override public boolean requery() { int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] == null) { continue; } if (mCursors[i].requery() == false) return false; } return true; } @Override public void unregisterDataSetObserver(DataSetObserver observer) { int length = mCursors.length; for (int i = 0; i < length; i++) { if (mCursors[i] != null) { mCursors[i].unregisterDataSetObserver(observer); } } } }