保存并搜索数据
最后更新于：2022-04-01 01:44:00
> 编写:[Lin-H](https://github.com/Lin-H) - 原文:[http://developer.android.com/training/search/search.html](http://developer.android.com/training/search/search.html)
有很多方法可以储存你的数据，比如储存在线上的数据库，本地的SQLite数据库，甚至是文本文件。你自己来选择最适合你应用的存储方式。本节课程会向你展示如何创建一个健壮的可以提供全文搜索的SQLite虚拟表。并从一个每行有一组单词-解释对的文件中将数据填入。
### 创建虚拟表
虚拟表与SQLite表的运行方式类似，但虚拟表是通过回调来向内存中的对象进行读取和写入，而不是通过数据库文件。要创建一个虚拟表，首先为该表创建一个类:
~~~
public class DatabaseTable {
private final DatabaseOpenHelper mDatabaseOpenHelper;
public DatabaseTable(Context context) {
mDatabaseOpenHelper = new DatabaseOpenHelper(context);
}
}
~~~
在`DatabaseTable`类中创建一个继承[SQLiteOpenHelper](http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html)的内部类。你必须重写类[SQLiteOpenHelper](http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html)中定义的abstract方法，才能在必要的时候创建和更新你的数据库表。例如，下面一段代码声明了一个数据库表，用来储存字典app所需的单词。
~~~
public class DatabaseTable {
private static final String TAG = "DictionaryDatabase";
//字典的表中将要包含的列项
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);
}
}
}
~~~
### 填入虚拟表
现在，表需要数据来储存。下面的代码会向你展示如何读取一个内容为单词和解释的文本文件(位于`res/raw/definitions.txt`)，如何解析文件与如何将文件中的数据按行插入虚拟表中。为防止UI锁死这些操作会在另一条线程中执行。将下面的一段代码添加到你的`DatabaseOpenHelper`内部类中。
> **Tip**:你也可以设置一个回调来通知你的UI [activity](# "An activity represents a single screen with a user interface.")线程的完成结果。
~~~
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);
}
~~~
任何恰当的地方，都可以调用`loadDictionary()`方法向表中填入数据。一个比较好的地方是`DatabaseOpenHelper`类的[onCreate()](http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html#onCreate(android.database.sqlite.SQLiteDatabase))方法中，紧随创建表之后:
~~~
@Override
public void onCreate(SQLiteDatabase db) {
mDatabase = db;
mDatabase.execSQL(FTS_TABLE_CREATE);
loadDictionary();
}
~~~
### 搜索请求
当你的虚拟表创建好并填入数据后，根据[SearchView](http://developer.android.com/reference/android/widget/SearchView.html)提供的请求搜索数据。将下面的方法添加到`DatabaseTable`类中，用来创建搜索请求的SQL语句:
~~~
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;
}
~~~
调用`getWordMatches()`来搜索请求。任何符合的结果返回到[Cursor](http://developer.android.com/reference/android/database/Cursor.html)中，可以直接遍历或是建立一个[ListView](http://developer.android.com/reference/android/widget/ListView.html)。这个例子是在检索[activity](# "An activity represents a single screen with a user interface.")的`handleIntent()`方法中调用`getWordMatches()`。请记住，因为之前创建的intent filter，检索[activity](# "An activity represents a single screen with a user interface.")会在[ACTION_SEARCH](http://developer.android.com/reference/android/content/Intent.html#ACTION_SEARCH) intent中额外接收请求作为变量存储:
~~~
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);
//执行Cursor并显示结果
}
}
~~~