Question

我正在制作一个Android应用程序来学习SQLite数据库。我有一个函数应该将用户的移动数据从加速度计写入数据库。使用以下命令创建数据库：

db.execSQL("create table if not exists data(ID integer primary key autoincrement, "+
"lat integer, long integer, "+
"movement real, "+
"time text);");

并且每2秒调用写入DB的函数：

void insertTable(float mov)
{

    db.beginTransaction();
    try
    {
        // this part gets the current time
        Calendar now = Calendar.getInstance();
        String date = now.get(Calendar.HOUR_OF_DAY)+":"+now.get(Calendar.MINUTE)+":"+now.get(Calendar.SECOND)+
        "."+now.get(Calendar.MILLISECOND)+" "+now.get(Calendar.DAY_OF_MONTH)+"/"+now.get(Calendar.MONTH)+
        "/"+now.get(Calendar.YEAR);


        db.execSQL("insert into data(movement ,time) values ("+
                mov+",'"+date+"');");
        Cursor c1 = db.rawQuery("select * from data", null);

                    // this happens after the 5th iteration and the app crashes
        if(numRefreshes>5) c1.moveToPosition(2);

                    // this happens the first 5 iterations of this function
        else c1.moveToPosition(0);

                    // get time and date and show it on the screen
        String datum = c1.getString(4);
        c1.close();
        dbResult.setText(datum);

                    // keep track of how many times this function has been called
        numRefreshes++;
    }
    catch(SQLiteException e)
    {
        Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_SHORT).show();
    }
    finally
    {
        db.endTransaction();
    }
}

如您所见，调用此函数的前5次将从表格的第1行打印日期。它始终显示插入的最后行的值。我想这很好。但是在第5次之后，当我尝试读取第3行的日期值时，它崩溃并且LogCat说：

FATAL EXCEPTION: main
android.database.CursorIndexOutOfBoundsException: Index 1 requested, with a size of 1

所以我假设SQLite每次都会覆盖我以前的行。我做错了什么？

Answer 1

看起来您没有调用将事务设置为成功的方法。

您需要在db.setTransactionSuccessful()

之后添加numRefreshes++;

如果你查看db.beginTransaction()的java文档，你会发现

db.beginTransaction();
try {
 ...
  db.setTransactionSuccessful();
} finally {
 db.endTransaction();
}

如果没有setTransactionSuccessful，您将回滚所做的任何插入

Android上的SQLite无法正确插入

1 个答案: