/*
 * Copyright (c) 2010-2011, The MiCode Open Source Community (www.micode.net)
 *
 * 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 net.micode.notes.data;

// 导入Android框架中用于ContentProvider的相关类
import android.app.SearchManager;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Intent;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;

// 导入应用内部定义的类和接口
import net.micode.notes.R;
import net.micode.notes.data.Notes.DataColumns;
import net.micode.notes.data.Notes.NoteColumns;
import net.micode.notes.data.NotesDatabaseHelper.TABLE;

// 继承ContentProvider类，创建NotesProvider类，用于管理笔记数据
public class NotesProvider extends ContentProvider {
    // Uri匹配器，用于识别不同的URI路径
    private static final UriMatcher mMatcher;

    // 数据库帮助类实例，用于操作数据库
    private NotesDatabaseHelper mHelper;

    // 日志标签，用于Log日志输出
    private static final String TAG = "NotesProvider";

    // 定义不同的URI代码，用于匹配不同的URI路径
    private static final int URI_NOTE            = 1;
    private static final int URI_NOTE_ITEM       = 2;
    private static final int URI_DATA            = 3;
    private static final int URI_DATA_ITEM       = 4;
    private static final int URI_SEARCH          = 5;
    private static final int URI_SEARCH_SUGGEST  = 6;

    // 静态初始化块，初始化Uri匹配器
    static {
        mMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        mMatcher.addURI(Notes.AUTHORITY, "note", URI_NOTE);
        mMatcher.addURI(Notes.AUTHORITY, "note/#", URI_NOTE_ITEM);
        mMatcher.addURI(Notes.AUTHORITY, "data", URI_DATA);
        mMatcher.addURI(Notes.AUTHORITY, "data/#", URI_DATA_ITEM);
        mMatcher.addURI(Notes.AUTHORITY, "search", URI_SEARCH);
        mMatcher.addURI(Notes.AUTHORITY, SearchManager.SUGGEST_URI_PATH_QUERY, URI_SEARCH_SUGGEST);
        mMatcher.addURI(Notes.AUTHORITY, SearchManager.SUGGEST_URI_PATH_QUERY + "/*", URI_SEARCH_SUGGEST);
    }

    // 定义搜索结果的投影，包括ID、摘要等信息
    /**
     * x'0A'代表sqlite中的'\n'字符。为了在搜索结果中显示更多信息，
     * 我们将截取标题和内容中的'\n'和空白。
     */
    private static final String NOTES_SEARCH_PROJECTION = NoteColumns.ID + ","
        + NoteColumns.ID + " AS " + SearchManager.SUGGEST_COLUMN_INTENT_EXTRA_DATA + ","
        + "TRIM(REPLACE(" + NoteColumns.SNIPPET + ", x'0A','')) AS " + SearchManager.SUGGEST_COLUMN_TEXT_1 + ","
        + "TRIM(REPLACE(" + NoteColumns.SNIPPET + ", x'0A','')) AS " + SearchManager.SUGGEST_COLUMN_TEXT_2 + ","
        + R.drawable.search_result + " AS " + SearchManager.SUGGEST_COLUMN_ICON_1 + ","
        + "'" + Intent.ACTION_VIEW + "' AS " + SearchManager.SUGGEST_COLUMN_INTENT_ACTION + ","
        + "'" + Notes.TextNote.CONTENT_TYPE + "' AS " + SearchManager.SUGGEST_COLUMN_INTENT_DATA;

    // 定义笔记摘要搜索查询
    private static String NOTES_SNIPPET_SEARCH_QUERY = "SELECT " + NOTES_SEARCH_PROJECTION
        + " FROM " + TABLE.NOTE
        + " WHERE " + NoteColumns.SNIPPET + " LIKE ?"
        + " AND " + NoteColumns.PARENT_ID + "<>" + Notes.ID_TRASH_FOLER
        + " AND " + NoteColumns.TYPE + "=" + Notes.TYPE_NOTE;

    // onCreate方法，初始化数据库帮助类实例
    @Override
    public boolean onCreate() {
        mHelper = NotesDatabaseHelper.getInstance(getContext());
        return true;
    }

    // query方法，处理查询请求
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
            String sortOrder) {
        Cursor c = null;
        SQLiteDatabase db = mHelper.getReadableDatabase();
        String id = null;
        // 根据URI匹配结果，执行不同的查询操作
        switch (mMatcher.match(uri)) {
            case URI_NOTE:
                // 查询笔记表
                c = db.query(TABLE.NOTE, projection, selection, selectionArgs, null, null,
                        sortOrder);
                break;
            case URI_NOTE_ITEM:
                // 查询单个笔记项
                id = uri.getPathSegments().get(1);
                c = db.query(TABLE.NOTE, projection, NoteColumns.ID + "=" + id
                        + parseSelection(selection), selectionArgs, null, null, sortOrder);
                break;
            case URI_DATA:
                // 查询数据表
                c = db.query(TABLE.DATA, projection, selection, selectionArgs, null, null,
                        sortOrder);
                break;
            case URI_DATA_ITEM:
                // 查询单个数据项
                id = uri.getPathSegments().get(1);
                c = db.query(TABLE.DATA, projection, DataColumns.ID + "=" + id
                        + parseSelection(selection), selectionArgs, null, null, sortOrder);
                break;
            case URI_SEARCH:
            case URI_SEARCH_SUGGEST:
                // 处理搜索请求
                if (sortOrder != null || projection != null) {
                    throw new IllegalArgumentException(
                            "do not specify sortOrder, selection, selectionArgs, or projection" + "with this query");
                }

                String searchString = null;
                if (mMatcher.match(uri) == URI_SEARCH_SUGGEST) {
                    if (uri.getPathSegments().size() > 1) {
                        searchString = uri.getPathSegments().get(1);
                    }
                } else {
                    searchString = uri.getQueryParameter("pattern");
                }

                if (TextUtils.isEmpty(searchString)) {
                    return null;
                }

                try {
                    searchString = String.format("%%%s%%", searchString);
                    c = db.rawQuery(NOTES_SNIPPET_SEARCH_QUERY,
                            new String[] { searchString });
                } catch (IllegalStateException ex) {
                    Log.e(TAG, "got exception: " + ex.toString());
                }
                break;
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
        // 设置通知URI，以便在数据变化时通知外界
        if (c != null) {
            c.setNotificationUri(getContext().getContentResolver(), uri);
        }
        return c;
    }
}

   
以下是对代码中关键部分的注释：

java
/**
 * 实现ContentProvider接口的insert方法，用于插入新的数据。
 * @param uri 请求的URI，用于确定插入数据的表。
 * @param values 包含要插入数据的ContentValues。
 * @return 插入数据的URI，包括ID。
 */
@Override
public Uri insert(Uri uri, ContentValues values) {
    // 获取可写数据库实例
    SQLiteDatabase db = mHelper.getWritableDatabase();
    long dataId = 0, noteId = 0, insertedId = 0;
    // 使用UriMatcher匹配URI，确定插入哪个表
    switch (mMatcher.match(uri)) {
        case URI_NOTE:
            // 插入笔记数据
            insertedId = noteId = db.insert(TABLE.NOTE, null, values);
            break;
        case URI_DATA:
            // 插入数据，如果包含笔记ID，则记录
            if (values.containsKey(DataColumns.NOTE_ID)) {
                noteId = values.getAsLong(DataColumns.NOTE_ID);
            } else {
                Log.d(TAG, "Wrong data format without note id:" + values.toString());
            }
            insertedId = dataId = db.insert(TABLE.DATA, null, values);
            break;
        default:
            // 如果URI不匹配，则抛出异常
            throw new IllegalArgumentException("Unknown URI " + uri);
    }
    // 如果插入笔记ID大于0，通知变化
    if (noteId > 0) {
        getContext().getContentResolver().notifyChange(
                ContentUris.withAppendedId(Notes.CONTENT_NOTE_URI, noteId), null);
    }
    // 如果插入数据ID大于0，通知变化
    if (dataId > 0) {
        getContext().getContentResolver().notifyChange(
                ContentUris.withAppendedId(Notes.CONTENT_DATA_URI, dataId), null);
    }
    // 返回插入数据的URI
    return ContentUris.withAppendedId(uri, insertedId);
}

/**
 * 实现ContentProvider接口的delete方法，用于删除数据。
 * @param uri 请求的URI，用于确定删除数据的表。
 * @param selection 删除条件。
 * @param selectionArgs 删除条件的参数。
 * @return 删除的行数。
 */
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
    int count = 0;
    String id = null;
    SQLiteDatabase db = mHelper.getWritableDatabase();
    boolean deleteData = false;
    // 使用UriMatcher匹配URI，确定删除哪个表
    switch (mMatcher.match(uri)) {
        case URI_NOTE:
            // 删除笔记数据，限制删除ID大于0的记录
            selection = "(" + selection + ") AND " + NoteColumns.ID + ">0 ";
            count = db.delete(TABLE.NOTE, selection, selectionArgs);
            break;
        case URI_NOTE_ITEM:
            // 删除单个笔记项
            id = uri.getPathSegments().get(1);
            long noteId = Long.valueOf(id);
            if (noteId <= 0) {
                break;
            }
            count = db.delete(TABLE.NOTE,
                    NoteColumns.ID + "=" + id + parseSelection(selection), selectionArgs);
            break;
        case URI_DATA:
            // 删除数据表中的记录
            count = db.delete(TABLE.DATA, selection, selectionArgs);
            deleteData = true;
            break;
        case URI_DATA_ITEM:
            // 删除单个数据项
            id = uri.getPathSegments().get(1);
            count = db.delete(TABLE.DATA,
                    DataColumns.ID + "=" + id + parseSelection(selection), selectionArgs);
            deleteData = true;
            break;
        default:
            // 如果URI不匹配，则抛出异常
            throw new IllegalArgumentException("Unknown URI " + uri);
    }
    // 如果删除了记录，通知变化
    if (count > 0) {
        if (deleteData) {
            getContext().getContentResolver().notifyChange(Notes.CONTENT_NOTE_URI, null);
        }
        getContext().getContentResolver().notifyChange(uri, null);
    }
    return count;
}

/**
 * 实现ContentProvider接口的update方法，用于更新数据。
 * @param uri 请求的URI，用于确定更新数据的表。
 * @param values 包含要更新数据的ContentValues。
 * @param selection 更新条件。
 * @param selectionArgs 更新条件的参数。
 * @return 更新的行数。
 */
@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
    int count = 0;
    String id = null;
    SQLiteDatabase db = mHelper.getWritableDatabase();
    boolean updateData = false;
    // 使用UriMatcher匹配URI，确定更新哪个表
    switch (mMatcher.match(uri)) {
        case URI_NOTE:
            // 更新笔记数据，增加版本号
            increaseNoteVersion(-1, selection, selectionArgs);
            count = db.update(TABLE.NOTE, values, selection, selectionArgs);
            break;
        case URI_NOTE_ITEM:
            // 更新单个笔记项
            id = uri.getPathSegments().get(1);
            increaseNoteVersion(Long.valueOf(id), selection, selectionArgs);
            count = db.update(TABLE.NOTE, values, NoteColumns.ID + "=" + id
                    + parseSelection(selection), selectionArgs);
            break;
        case URI_DATA:
            // 更新数据表中的记录
            count = db.update(TABLE.DATA, values, selection, selectionArgs);
            updateData = true;
            break;
        case URI_DATA_ITEM:
            // 更新单个数据项
            id = uri.getPathSegments().get(1);
            count = db.update(TABLE.DATA, values, DataColumns.ID + "=" + id
                    + parseSelection(selection), selectionArgs);
            updateData = true;
            break;
        default:
            // 如果URI不匹配，则抛出异常
            throw new IllegalArgumentException("Unknown URI " + uri);
    }
    // 如果更新了记录，通知变化
    if (count > 0) {
        if (updateData) {
            getContext().getContentResolver().notifyChange(Notes.CONTENT_NOTE_URI, null);
        }
        getContext().getContentResolver().notifyChange(uri, null);
    }
    return count;
}

/**
 * 解析选择条件，添加AND前缀。
 * @param selection 选择条件。
 * @return 处理后的选择条件。
 */
private String parseSelection(String selection) {
    return (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : "");
}

/**
 * 增加笔记的版本号。
 * @param id 笔记ID，-1表示更新所有匹配的记录。
 * @param selection 更新条件。
 * @param selectionArgs 更新条件的参数。
 */
private void increaseNoteVersion(long id, String selection, String[] selectionArgs) {
    // 构建SQL语句，增加版本号
    StringBuilder sql = new StringBuilder(120);
    sql.append("UPDATE ");
    sql.append(TABLE.NOTE);
    sql.append(" SET ");
    sql.append(NoteColumns.VERSION);
    sql.append("=" + NoteColumns.VERSION + "+1 ");

    if (id > 0 || !TextUtils.isEmpty(selection)) {
        sql.append(" WHERE ");
    }
    if (id > 0) {
        sql.append(NoteColumns.ID + "=" + String.valueOf(id));
    }
    if (!TextUtils.isEmpty(selection)) {
        String selectString = id > 0 ? parseSelection(selection) : selection;
        for (String args : selectionArgs) {
            selectString = selectString.replaceFirst("\\?", args);
        }
        sql.append(selectString);
    }

    // 执行SQL语句
    mHelper.getWritableDatabase().execSQL(sql.toString());
}

/**
 * 实现ContentProvider接口的getType方法，用于获取数据类型。
 * @param uri 请求的URI。
 * @return 数据类型，此方法未实现返回null。
 */
@Override
public String getType(Uri uri) {
    // TODO Auto-generated method stub
    return null;
    }
}