有很多方法可以儲(chǔ)存你的數(shù)據(jù)，比如儲(chǔ)存在線上的數(shù)據(jù)庫，本地的SQLite數(shù)據(jù)庫，甚至是文本文件。你自己來選擇最適合你應(yīng)用的存儲(chǔ)方式。本節(jié)課程會(huì)向你展示如何創(chuàng)建一個(gè)健壯的可以提供全文搜索的SQLite虛擬表。并從一個(gè)每行有一組單詞-解釋對的文件中將數(shù)據(jù)填入。

創(chuàng)建虛擬表

虛擬表與SQLite表的運(yùn)行方式類似，但虛擬表是通過回調(diào)來向內(nèi)存中的對象進(jìn)行讀取和寫入，而不是通過數(shù)據(jù)庫文件。要?jiǎng)?chuàng)建一個(gè)虛擬表，首先為該表創(chuàng)建一個(gè)類:

public class DatabaseTable {
    private final DatabaseOpenHelper mDatabaseOpenHelper;

    public DatabaseTable(Context context) {
        mDatabaseOpenHelper = new DatabaseOpenHelper(context);
    }
}

在DatabaseTable類中創(chuàng)建一個(gè)繼承SQLiteOpenHelper的內(nèi)部類。你必須重寫類SQLiteOpenHelper中定義的abstract方法，才能在必要的時(shí)候創(chuàng)建和更新你的數(shù)據(jù)庫表。例如，下面一段代碼聲明了一個(gè)數(shù)據(jù)庫表，用來儲(chǔ)存字典app所需的單詞。

public class DatabaseTable {

    private static final String TAG = "DictionaryDatabase";

    //字典的表中將要包含的列項(xiàng)
    public static final String COL_WORD = "WORD";
    public static final String COL_DEFINITION = "DEFINITION";

    private static final String DATABASE_NAME = "DICTIONARY";
    private static final String FTS_VIRTUAL_TABLE = "FTS";
    private static final int DATABASE_VERSION = 1;

    private final DatabaseOpenHelper mDatabaseOpenHelper;

    public DatabaseTable(Context context) {
        mDatabaseOpenHelper = new DatabaseOpenHelper(context);
    }

    private static class DatabaseOpenHelper extends SQLiteOpenHelper {

        private final Context mHelperContext;
        private SQLiteDatabase mDatabase;

        private static final String FTS_TABLE_CREATE =
                    "CREATE VIRTUAL TABLE " + FTS_VIRTUAL_TABLE +
                    " USING fts3 (" +
                    COL_WORD + ", " +
                    COL_DEFINITION + ")";

        DatabaseOpenHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
            mHelperContext = context;
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            mDatabase = db;
            mDatabase.execSQL(FTS_TABLE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS " + FTS_VIRTUAL_TABLE);
            onCreate(db);
        }
    }
}

填入虛擬表

現(xiàn)在，表需要數(shù)據(jù)來儲(chǔ)存。下面的代碼會(huì)向你展示如何讀取一個(gè)內(nèi)容為單詞和解釋的文本文件(位于res/raw/definitions.txt)，如何解析文件與如何將文件中的數(shù)據(jù)按行插入虛擬表中。為防止UI鎖死這些操作會(huì)在另一條線程中執(zhí)行。將下面的一段代碼添加到你的DatabaseOpenHelper內(nèi)部類中。

Tip:你也可以設(shè)置一個(gè)回調(diào)來通知你的UI activity線程的完成結(jié)果。

private void loadDictionary() {
        new Thread(new Runnable() {
            public void run() {
                try {
                    loadWords();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }).start();
    }

private void loadWords() throws IOException {
    final Resources resources = mHelperContext.getResources();
    InputStream inputStream = resources.openRawResource(R.raw.definitions);
    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

    try {
        String line;
        while ((line = reader.readLine()) != null) {
            String[] strings = TextUtils.split(line, "-");
            if (strings.length < 2) continue;
            long id = addWord(strings[0].trim(), strings[1].trim());
            if (id < 0) {
                Log.e(TAG, "unable to add word: " + strings[0].trim());
            }
        }
    } finally {
        reader.close();
    }
}

public long addWord(String word, String definition) {
    ContentValues initialValues = new ContentValues();
    initialValues.put(COL_WORD, word);
    initialValues.put(COL_DEFINITION, definition);

    return mDatabase.insert(FTS_VIRTUAL_TABLE, null, initialValues);
}

任何恰當(dāng)?shù)牡胤?，都可以調(diào)用loadDictionary()方法向表中填入數(shù)據(jù)。一個(gè)比較好的地方是DatabaseOpenHelper類的onCreate()方法中，緊隨創(chuàng)建表之后:

@Override
public void onCreate(SQLiteDatabase db) {
    mDatabase = db;
    mDatabase.execSQL(FTS_TABLE_CREATE);
    loadDictionary();
}

搜索請求

當(dāng)你的虛擬表創(chuàng)建好并填入數(shù)據(jù)后，根據(jù)SearchView提供的請求搜索數(shù)據(jù)。將下面的方法添加到DatabaseTable類中，用來創(chuàng)建搜索請求的SQL語句:

public Cursor getWordMatches(String query, String[] columns) {
    String selection = COL_WORD + " MATCH ?";
    String[] selectionArgs = new String[] {query+"*"};

    return query(selection, selectionArgs, columns);
}

private Cursor query(String selection, String[] selectionArgs, String[] columns) {
    SQLiteQueryBuilder builder = new SQLiteQueryBuilder();
    builder.setTables(FTS_VIRTUAL_TABLE);

    Cursor cursor = builder.query(mDatabaseOpenHelper.getReadableDatabase(),
            columns, selection, selectionArgs, null, null, null);

    if (cursor == null) {
        return null;
    } else if (!cursor.moveToFirst()) {
        cursor.close();
        return null;
    }
    return cursor;
}

調(diào)用getWordMatches()來搜索請求。任何符合的結(jié)果返回到Cursor中，可以直接遍歷或是建立一個(gè)ListView。這個(gè)例子是在檢索activity的handleIntent()方法中調(diào)用getWordMatches()。請記住，因?yàn)橹皠?chuàng)建的intent filter，檢索activity會(huì)在ACTION_SEARCH intent中額外接收請求作為變量存儲(chǔ):

DatabaseTable db = new DatabaseTable(this);

...

private void handleIntent(Intent intent) {

    if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
        String query = intent.getStringExtra(SearchManager.QUERY);
        Cursor c = db.getWordMatches(query, null);
        //執(zhí)行Cursor并顯示結(jié)果
    }
}

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