MiNotes/other/06_210340012金宏武_代码标注/NotesProvider.java

package net.micode.notes.data;
//说明当前文件所在包

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;

//为存储和获取数据提供接口。可以在不同的应用程序之间共享数据
//ContentProvider提供的方法
//query：查询
//insert：插入
//update：更新
//delete：删除
//getType：得到数据类型
public class NotesProvider extends ContentProvider {
    // UriMatcher用于匹配Uri
    private static final UriMatcher mMatcher;
    //数据库辅助类的实例对象
    private NotesDatabaseHelper mHelper;
    //写入日志时的标签名
    private static final String TAG = "NotesProvider";
    //Uri资源的ID共6个
    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 {
        // 创建UriMatcher时，调用UriMatcher(UriMatcher.NO_MATCH)表示不匹配任何路径的返回码
        mMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        // 把需要匹配Uri路径全部给注册上
        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.
     */
    // 声明 字符串NOTES_SEARCH_PROJECTION,作为实参，相当于where语句
    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;
    // 声明NOTES_SNIPPET_SEARCH_QUERY，作用同上
    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;

    @Override
    // Context只有在onCreate()中才被初始化
    // 对mHelper进行实例化
    public boolean onCreate() {
        mHelper = NotesDatabaseHelper.getInstance(getContext());
        return true;
    }

    @Override
    // 查询uri在数据库中对应的位置
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
                        String sortOrder) {
        //先声明一个游标
        Cursor c = null;
        // 获取可读数据库
        SQLiteDatabase db = mHelper.getReadableDatabase();
        String id = null;
        // 匹配查找uri
        switch (mMatcher.match(uri)) {
            // 对于不同的匹配值，在数据库中查找相应的条目
            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) {
                    // 不合法的参数异常
                    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) {
                        // getPathSegments()方法得到一个String的List，
                        // 在uri.getPathSegments().get(1)为第2个元素
                        searchString = uri.getPathSegments().get(1);
                    }
                } else {
                    //利用URi的getQueryParameter方法可以获取字符串参数
                    searchString = uri.getQueryParameter("pattern");
                }

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

                try {
                    searchString = String.format("%%%s%%", searchString);
                    //通过上文得到的搜索字符串进行格式加工，然后用于下面数据库查询条件
                    c = db.rawQuery(NOTES_SNIPPET_SEARCH_QUERY,
                            new String[] { searchString });
                } catch (IllegalStateException ex) {
                    //捕捉异常
                    Log.e(TAG, "got exception: " + ex.toString());
                }
                break;
            default:
                // 抛出异常
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
        if (c != null) {
            //若getContentResolver发生变化，就接收通知
            c.setNotificationUri(getContext().getContentResolver(), uri);
        }
        return c;
    }

    @Override
    // 插入一个uri
    public Uri insert(Uri uri, ContentValues values) {
        // 获得可写的数据库
        SQLiteDatabase db = mHelper.getWritableDatabase();
        long dataId = 0, noteId = 0, insertedId = 0;
        switch (mMatcher.match(uri)) {
            // 新增一个条目
            case URI_NOTE:
                insertedId = noteId = db.insert(TABLE.NOTE, null, values);
                break;
            // 如果存在，查找NOTE_ID
            case URI_DATA:
                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:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
        // Notify the note uri
        // 获的一个content对象，若发生了变化则调用getContentResolver，由notifyChange对监听它的对象进行通知
        if (noteId > 0) {
            getContext().getContentResolver().notifyChange(
                    ContentUris.withAppendedId(Notes.CONTENT_NOTE_URI, noteId), null);
        }

        // Notify the data uri
        //更新Data ID
        if (dataId > 0) {
            getContext().getContentResolver().notifyChange(
                    ContentUris.withAppendedId(Notes.CONTENT_DATA_URI, dataId), null);
        }

        // 返回插入的uri的路径
        return ContentUris.withAppendedId(uri, insertedId);
    }

    @Override
    // 删除一个uri
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        //Uri代表要操作的数据，Android上可用的每种资源 -包括 图像、视频片段、音频资源等都可以用Uri来表示。
        int count = 0;
        String id = null;
        // 获得可写的数据库
        SQLiteDatabase db = mHelper.getWritableDatabase();
        boolean deleteData = false;
        switch (mMatcher.match(uri)) {
            case URI_NOTE:
                //筛选语句如下
                selection = "(" + selection + ") AND " + NoteColumns.ID + ">0 ";
                //删除相应数据
                count = db.delete(TABLE.NOTE, selection, selectionArgs);
                break;
            case URI_NOTE_ITEM:
                id = uri.getPathSegments().get(1);
                /**
                 * ID that smaller than 0 is system folder which is not allowed to
                 * trash
                 */
                long noteId = Long.valueOf(id);
                //将ID值转为长整数
                if (noteId <= 0) {
                    break;
                }
                //执行删除操作，三个参数分别为要删除的表，删除筛选条件，
                count = db.delete(TABLE.NOTE,
                        NoteColumns.ID + "=" + id + parseSelection(selection), selectionArgs);
                break;
            case URI_DATA:
                count = db.delete(TABLE.DATA, selection, selectionArgs);
                deleteData = true;
                break;
            case URI_DATA_ITEM:
                id = uri.getPathSegments().get(1);
                count = db.delete(TABLE.DATA,
                        DataColumns.ID + "=" + id + parseSelection(selection), selectionArgs);
                deleteData = true;
                break;
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
        if (count > 0) {
            //判断是否进行了删除操作，并对监听了删除操作的其他部分给予提醒
            if (deleteData) {
                getContext().getContentResolver().notifyChange(Notes.CONTENT_NOTE_URI, null);
            }
            getContext().getContentResolver().notifyChange(uri, null);
        }
        return count;
    }

    @Override
    // 更新一个uri
    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:
                //note版本更新，数据更新，以下各部分一致
                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:
                //查询异常处理
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
        //在执行了更新的操作之后，要对监听更新操作的其他部分给予提醒
        if (count > 0) {
            if (updateData) {
                getContext().getContentResolver().notifyChange(Notes.CONTENT_NOTE_URI, null);
            }
            getContext().getContentResolver().notifyChange(uri, null);
        }
        return count;
    }

    // 将字符串解析成规定格式
    private String parseSelection(String selection) {
        return (!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : "");
    }

    //增加一个noteVersion
    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);
        }

        // execSQL()方法可以执行insert、delete、update和CREATE TABLE之类有更改行为的SQL语句
        mHelper.getWritableDatabase().execSQL(sql.toString());
    }

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

}