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Android example source code file (SortCursor.java)

This example Android source code file (SortCursor.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

abstractcursor, android, cursor, database, datasetobserver, illegalstateexception, no, override, rowcachesize, sortcursor, string, tag, util, utilities, utils

The SortCursor.java Android example source code

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * 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.android.internal.database;

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 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 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 boolean deleteRow()
    {
        return mCursor.deleteRow();
    }

    @Override
    public boolean commitUpdates() {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].commitUpdates();
            }
        }
        onChange(true);
        return true;
    }

    @Override
    public String getString(int column)
    {
        return mCursor.getString(column);
    }

    @Override
    public short getShort(int column)
    {
        return mCursor.getShort(column);
    }

    @Override
    public int getInt(int column)
    {
        return mCursor.getInt(column);
    }

    @Override
    public long getLong(int column)
    {
        return mCursor.getLong(column);
    }

    @Override
    public float getFloat(int column)
    {
        return mCursor.getFloat(column);
    }

    @Override
    public double getDouble(int column)
    {
        return mCursor.getDouble(column);
    }

    @Override
    public boolean isNull(int column)
    {
        return mCursor.isNull(column);
    }

    @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 void deactivate()
    {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] == null) continue;
            mCursors[i].deactivate();
        }
    }

    @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 registerDataSetObserver(DataSetObserver observer) {
        int length = mCursors.length;
        for (int i = 0 ; i < length ; i++) {
            if (mCursors[i] != null) {
                mCursors[i].registerDataSetObserver(observer);
            }
        }
    }
    
    @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);
            }
        }
    }
    
    @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;
    }
}

Other Android examples (source code examples)

Here is a short list of links related to this Android SortCursor.java source code file:

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