motify/NotesProvider.java

/*
 * 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;


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;

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;

//NotesProvider是一个ContentProvider，它提供与Note相关的数据。提供Note的增删改查，以及搜索功能。
public class NotesProvider extends ContentProvider {
    //UriMatcher是用来匹配URI的。通过addURI来添加URI的匹配规则。
    private static final UriMatcher mMatcher;


  //  NotesDatabaseHelper是一个单例的DatabaseHelper，用来管理数据库。
    private NotesDatabaseHelper mHelper;
//TAG用于调试日志。
    private static final String TAG = "NotesProvider";
//下面定义了6个URI匹配规则。用于匹配Note和Data表，以及搜索功能。
    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;

    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);
    }

    /**
     * x'0A' represents the '\n' character in sqlite. For title and content in the search result,
     * we will trim '\n' and white space in order to show more information.
     */
    //下面是搜索功能的查询语句。它查询Note表，将查询结果的部分信息用于搜索功能展示。
    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;

    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;

    //ContentProvider的回调方法，用于初始化DatabaseHelper。
    @Override
    public boolean onCreate() {
        mHelper = NotesDatabaseHelper.getInstance(getContext());
        return true;
    }
//ContentProvider的回调方法，用于查询数据。
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
            String sortOrder) {
        Cursor c = null;
        SQLiteDatabase db = mHelper.getReadableDatabase();
        String id = null;
        //执行对ContentProvider的查询
        //@param uri 请求的内容的URI
        //@param projection 结果集中所包含的列
        //@param selection 过滤器
        //@param selectionArgs 过滤器的参数
        //@param sortOrder 排序方式
        //@return 查询结果
        switch (mMatcher.match(uri)) {
            case URI_NOTE:
                c = db.query(TABLE.NOTE, projection, selection, selectionArgs, null, null,
                        sortOrder);
                break;
            case URI_NOTE_ITEM:
                id = uri.getPathSegments().get(1);
                c = db.query(TABLE.NOTE, projection, NoteColumns.ID + "=" + id
                        + parseSelection(selection), selectionArgs, null, null, sortOrder);
                break;
            case URI_DATA:
                c = db.query(TABLE.DATA, projection, selection, selectionArgs, null, null,
                        sortOrder);
                break;
            case URI_DATA_ITEM:
                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:
                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);
        }
        if (c != null) {
            c.setNotificationUri(getContext().getContentResolver(), uri);
        }
        return c;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) { // 插入数据
        SQLiteDatabase db = mHelper.getWritableDatabase(); // 获取可写的数据库实例
        long dataId = 0, noteId = 0, insertedId = 0; // 定义数据ID、笔记ID、插入的ID
        switch (mMatcher.match(uri)) { // 根据URI匹配对应的表格
            case URI_NOTE: // 笔记表格
                insertedId = noteId = db.insert(TABLE.NOTE, null, values); // 插入数据并返回插入行的ID
                break;
            case URI_DATA: // 数据表格
                if (values.containsKey(DataColumns.NOTE_ID)) { // 如果插入的内容包含笔记ID，则获取笔记ID
                    noteId = values.getAsLong(DataColumns.NOTE_ID);
                } else {
                    Log.d(TAG, "Wrong data format without note id:" + values.toString()); // 如果没有笔记ID，则打印错误信息
                }
                insertedId = dataId = db.insert(TABLE.DATA, null, values); // 将数据插入表格并返回行的ID
                break;
            default: // 不匹配任何表格，则抛出异常
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
// 通知URI发生了变化
        if (noteId > 0) {
            getContext().getContentResolver().notifyChange(
                    ContentUris.withAppendedId(Notes.CONTENT_NOTE_URI, noteId), null);
        }
        if (dataId > 0) {
            getContext().getContentResolver().notifyChange(
                    ContentUris.withAppendedId(Notes.CONTENT_DATA_URI, dataId), null);
        }
        return ContentUris.withAppendedId(uri, insertedId); // 返回插入内容的URI
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) { // 删除数据
        int count = 0; // 定义删除的行数
        String id = null;
        SQLiteDatabase db = mHelper.getWritableDatabase(); // 获取可写的数据库实例
        boolean deleteData = false;
        switch (mMatcher.match(uri)) { // 根据URI匹配对应的表格
            case URI_NOTE: // 笔记表格
// 构建删除所需的条件语句
                selection = "(" + selection + ") AND " + NoteColumns.ID + ">0 ";
                count = db.delete(TABLE.NOTE, selection, selectionArgs); // 删除匹配条件的行
                break;
            case URI_NOTE_ITEM: // 笔记表格
                id = uri.getPathSegments().get(1); // 获取路径中的ID
/**
 * ID that smaller than 0 is system folder which is not allowed to
 * trash
 */
                long noteId = Long.valueOf(id);
                if (noteId <= 0) { // 如果ID小于等于0，则不允许删除
                    break;
                }
                count = db.delete(TABLE.NOTE,
                        NoteColumns.ID + "=" + id + parseSelection(selection), selectionArgs); // 删除匹配条件的行
                break;
            case URI_DATA: // 数据表格
                count = db.delete(TABLE.DATA, selection, selectionArgs); // 删除匹配条件的行
                deleteData = true;
                break;
            case URI_DATA_ITEM: // 数据表格
                id = uri.getPathSegments().get(1); // 获取路径中的ID
                count = db.delete(TABLE.DATA,
                        DataColumns.ID + "=" + id + parseSelection(selection), selectionArgs); // 删除匹配条件的行
                deleteData = true;
                break;
            default: // 不匹配任何表格，则抛出异常
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
        if (count > 0) { // 如果有行被删除
            if (deleteData) { // 如果删除的是数据表格，则需要通知笔记URI发生变化
                getContext().getContentResolver().notifyChange(Notes.CONTENT_NOTE_URI, null);
            }
// 通知URI发生了变化
            getContext().getContentResolver().notifyChange(uri, null);
        }
        return count; // 返回已删除的行数
    }

    @Override
    //更新数据
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        int count = 0;
        String id = null;
        SQLiteDatabase db = mHelper.getWritableDatabase();
        boolean updateData = false;
        switch (mMatcher.match(uri)) {
            case URI_NOTE:
                increaseNoteVersion(-1, selection, selectionArgs);
                count = db.update(TABLE.NOTE, values, selection, selectionArgs);
                break;
            case URI_NOTE_ITEM:
                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:
                count = db.update(TABLE.DATA, values, selection, selectionArgs);
                updateData = true;
                break;
            case URI_DATA_ITEM:
                id = uri.getPathSegments().get(1);
                count = db.update(TABLE.DATA, values, DataColumns.ID + "=" + id
                        + parseSelection(selection), selectionArgs);
                updateData = true;
                break;
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }

        if (count > 0) {
            if (updateData) {
                getContext().getContentResolver().notifyChange(Notes.CONTENT_NOTE_URI, null);
            }
            getContext().getContentResolver().notifyChange(uri, null);
        }
        return count;
    }

    private String parseSelection(String selection) {
        return (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : "");
    }

    private void increaseNoteVersion(long id, String selection, String[] selectionArgs) {
        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);
        }

        mHelper.getWritableDatabase().execSQL(sql.toString());
    }

    @Override
    // 获取URI类型
    public String getType(Uri uri) {
        // TODO Auto-generated method stub
        return null;
    }

}