在后台线程中打开Sqlite数据库 [英] Opening an Sqlite database in a background thread

问题描述

我想更好地了解在Android的后台线程中打开一个Sqlite数据库的意义。现在我通过我的类 DatabaseHelper 为我的数据库使用一个静态/单例模式，所以我只需要打开一次，但我想使用良好的做法打开它，理解为什么我不应该直接从我的 Activity （或者在帮助器的构造函数中）打开它。

I am trying to better understand what it means to open an Sqlite database on a background thread in Android. Right now I am using a static/singleton pattern for my database via my class DatabaseHelper, so I only need to open it once, but I want to open it using good practice and understand why I shouldn't open it directly from within my Activity directly (or within the helper's constructor, for example).

我的类：

public class DatabaseHelper extends SQLiteOpenHelper {
    private static volatile SQLiteDatabase mDatabase;
    private static DatabaseHelper mInstance = null;
    private static Context mContext;

    // ...

    public static synchronized DatabaseHelper getInstance(Context context) {
        /**
         * use the application context as suggested by CommonsWare.
         * this will ensure that you don't accidentally leak an Activity's
         * context (see this article for more information:
         * http://android-developers.blogspot.nl/2009/01/avoiding-memory-leaks.html)
         */
        if (mInstance == null) {
            mInstance = new DatabaseHelper(context.getApplicationContext());
        }
        return mInstance;
    }

    private DatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
        mContext = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(DB_CREATE_SOME_TABLE); //some SQL expression
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
        db.execSQL(DB_ALTER);
    }

    public void open() throws SQLException {
        mDatabase = getWritableDatabase();
    }

    public void close() {
        mDatabase.close();
    }

    public boolean isOpen() {
        return mDatabase.isOpen();
    }

    //below this would be various CRUD functions operating on mDatabase
    // ...
    // ...
}

这是正确的说，你应该这样做：

Is it correct to say that you should do something like this:

   DatabaseHelper mDatabaseHelper = DatabaseHelper.getInstance(this);

   Thread thread = new Thread("OpenDbThread") {
      public void run(){
        mDatabaseHelper.open();
      }
   };


   thread.start();

在活动 >

推荐答案

你写的代码在后台线程上打开数据库是正确的。但是，您实际上不会打开数据库，直到 thread.isAlive（）返回false（或 mDatabase.isOpen（）返回true）。或者，您可以让您的活动侦听来自您的主题的回调。

You're correct that the code you wrote would open the database on a background thread. However, you wouldn't actually the database was opened until thread.isAlive() returned false (or mDatabase.isOpen() returned true). Alternatively, you could make your Activity listen for a callback from your Thread.

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