MatrixCursor 与 AbstractCursor实现Cursor 封装

Contacts 模块中：

protected synchronized void onQueryComplete(int token, Object cookie, Cursor cursor)

查询得到一个Cursor, 源码中对此cursor 作了一下封装， 生成一个新的Cursor, 代码如下：

Cursor mContactsCursor = new ExtendedCursor(
                    cursor, CallLogContactQuery.SECTION_NAME, CallLogContactQuery.SECTION_CONTACT_ITEM);

而ExtendedCursor  extends AbstractCursor ，下面是ExtendedCursor.java 的代码实现：

/*
 * Copyright (C) 2011 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.contacts.calllog;

import android.database.AbstractCursor;
import android.database.ContentObserver;
import android.database.Cursor;
import android.database.DataSetObserver;

import com.android.common.io.MoreCloseables;

/**
 * Wraps a cursor to add an additional column with the same value for all rows.
 * 

 * The number of rows in the cursor and the set of columns is determined by the cursor being
 * wrapped.
 */
public class ExtendedCursor extends AbstractCursor {
    /** The cursor to wrap. */
    private final Cursor mCursor;
    /** The name of the additional column. */
    private final String mColumnName;
    /** The value to be assigned to the additional column. */
    private final Object mValue;

    /**
     * Creates a new cursor which extends the given cursor by adding a column with a constant value.
     *
     * @param cursor the cursor to extend
     * @param columnName the name of the additional column
     * @param value the value to be assigned to the additional column
     */
    public ExtendedCursor(Cursor cursor, String columnName, Object value) {
        mCursor = cursor;
        mColumnName = columnName;
        mValue = value;
    }

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

    @Override
    public String[] getColumnNames() {
        String[] columnNames = mCursor.getColumnNames();
        int length = columnNames.length;
        String[] extendedColumnNames = new String[length + 1];
        System.arraycopy(columnNames, 0, extendedColumnNames, 0, length);
        extendedColumnNames[length] = mColumnName;
        return extendedColumnNames;
    }

    @Override
    public String getString(int column) {
        if (column == mCursor.getColumnCount()) {
            return (String) mValue;
        }
        return mCursor.getString(column);
    }

    @Override
    public short getShort(int column) {
        if (column == mCursor.getColumnCount()) {
            return (Short) mValue;
        }
        return mCursor.getShort(column);
    }

    @Override
    public int getInt(int column) {
        if (column == mCursor.getColumnCount()) {
            return (Integer) mValue;
        }
        return mCursor.getInt(column);
    }

    @Override
    public long getLong(int column) {
        if (column == mCursor.getColumnCount()) {
            return (Long) mValue;
        }
        return mCursor.getLong(column);
    }

    @Override
    public float getFloat(int column) {
        if (column == mCursor.getColumnCount()) {
            return (Float) mValue;
        }
        return mCursor.getFloat(column);
    }

    @Override
    public double getDouble(int column) {
        if (column == mCursor.getColumnCount()) {
            return (Double) mValue;
        }
        return mCursor.getDouble(column);
    }

    @Override
    public boolean isNull(int column) {
        if (column == mCursor.getColumnCount()) {
            return mValue == null;
        }
        return mCursor.isNull(column);
    }

    @Override
    public boolean onMove(int oldPosition, int newPosition) {
        return mCursor.moveToPosition(newPosition);
    }

    @Override
    public void close() {
        MoreCloseables.closeQuietly(mCursor);
        super.close();
    }

    @Override
    public void registerContentObserver(ContentObserver observer) {
        mCursor.registerContentObserver(observer);
    }

    @Override
    public void unregisterContentObserver(ContentObserver observer) {
        mCursor.unregisterContentObserver(observer);
    }

    @Override
    public void registerDataSetObserver(DataSetObserver observer) {
        mCursor.registerDataSetObserver(observer);
    }

    @Override
    public void unregisterDataSetObserver(DataSetObserver observer) {
        mCursor.unregisterDataSetObserver(observer);
    }
}

MatrixCursor 实现cursor封装, 同样是protected synchronized void onQueryComplete(int token, Object cookie,Cursor cursor)

得到一个cursor,  现在通过MatrixCursor对这个cursor 进行过滤（实际上跟封装是一个意思），：

MatrixCursor allCursor = new MatrixCursor(ALL_THREADS_PROJECTION);
                                while (cursor.moveToNext()) {
                                    String recipientIds = cursor.getString(RECIPIENT_IDS);
                                    //Log.e(TAG, "newView: " + recipientIds);
                                    boolean resultStrange = isTypeStrange ? !normalRecipient(recipientIds) /*Strange message*/ : normalRecipient(recipientIds); /*Contact message*/
                                    if (resultStrange) {
                                        replaceCursorValue(allCursor, cursor);
                                         }
                                    }

                                //Log.e(TAG, "newCur: " + allCursor.getCount());
                                allCursor.moveToPosition(-1);

resultStrange 主要判断是不是联系人还是陌生人， 相关函数调用如下：

        private void replaceCursorValue(MatrixCursor newCursor, Cursor oldCursor) {

            newCursor.addRow(new Object[] {
                    oldCursor.getLong(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[0])),
                    oldCursor.getLong(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[1])),
                    oldCursor.getLong(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[2])),
                    oldCursor.getString(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[3])),
                    oldCursor.getString(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[4])),
                    oldCursor.getInt(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[5])),
                    oldCursor.getInt(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[6])),
                    oldCursor.getInt(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[7])),
                    oldCursor.getInt(oldCursor
                            .getColumnIndex(Conversation.ALL_THREADS_PROJECTION[8]))
            });

        }

   public static final String[] ALL_THREADS_PROJECTION = {
        Threads._ID, Threads.DATE, Threads.MESSAGE_COUNT, Threads.RECIPIENT_IDS,
        Threads.SNIPPET, Threads.SNIPPET_CHARSET, Threads.READ, Threads.ERROR,
        Threads.HAS_ATTACHMENT
    };