尝试在我的 Android 应用程序中加载然后查询和 SQLite 数据库 - 严重难倒

Question

基本上我想做的是从我的资产文件夹加载我的数据库（romskillDB.db），然后查询我想要的信息。我尝试了几乎在网上可以找到的所有数据库帮助程序类，我尝试研究了所述帮助程序类调用的每个方法，我什至采用了示例代码，复制了它，然后尝试使其适应我的需要。一切都无济于事。因此，这是我在放弃并将数据硬编码到 .xml 文件中的广泛列表中之前获得所需答案的最后努力。请查看下面的代码，非常感谢您花时间提供帮助。

这是显示结果的类。

package com.rom.testdb;

import java.io.IOException;
import com.rom.testdb.DbUtils;
import android.app.ListActivity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.widget.TextView;

public class testDB extends ListActivity {

    SQLiteDatabase db;
    DbUtils dbUtil;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        dbUtil = new DbUtils();

        try {
            DbUtils.createDatabaseIfNotExists(this);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


        SQLiteDatabase db = DbUtils.getStaticDb();

        String table = "magegeneral";
        String[] columns = {"_id", "name"};
        Cursor cursor = db.query(table, columns, null, null, null, null, null);
        startManagingCursor(cursor);
        cursor.moveToFirst();  
        int thisId = cursor.getInt(0);
        String thisName = cursor.getString(1);
        cursor.close();

        TextView textview = new TextView(this);
        textview.setText(thisId + " " + thisName);
        setContentView(textview);

    }
}

这是帮助程序代码。

package com.rom.testdb;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;

public class DbUtils {
    private static final String DB_PATH = "/data/data/com.rom.testdb/databases/";
    private static final String DB_NAME = "romskillDB.db";

    public static void createDatabaseIfNotExists(Context context) throws IOException {
        boolean createDb = false;

        File dbDir = new File(DB_PATH);
        File dbFile = new File(DB_PATH + DB_NAME);
        if (!dbDir.exists()) {
            dbDir.mkdir();
            createDb = true;
        }
        else if (!dbFile.exists()) {
            createDb = true;
        }
        else {
            // Check that we have the latest version of the db
            boolean doUpgrade = false;

            // Insert your own logic here on whether to upgrade the db; I personally
            // just store the db version # in a text file, but you can do whatever
            // you want.  I've tried MD5 hashing the db before, but that takes a while.

            // If we are doing an upgrade, basically we just delete the db then
            // flip the switch to create a new one
            if (doUpgrade) {
                dbFile.delete();
                createDb = true;
            }
        }

        if (createDb) {
            // Open your local db as the input stream
            InputStream myInput = context.getAssets().open(DB_NAME);

            // Open the empty db as the output stream
            OutputStream myOutput = new FileOutputStream(dbFile);

            // transfer bytes from the inputfile to the outputfile
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }

            // Close the streams
            myOutput.flush();
            myOutput.close();
            myInput.close();
        }
    }

    public static SQLiteDatabase getStaticDb() {
        return SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null, SQLiteDatabase.OPEN_READONLY);
    }
}

再次感谢您的宝贵时间！

Answer 1

有两个问题可能会导致这种迷恋——
一个。这是您在内部运行的列表活动，尝试使用 getApplicationContext() 启动数据库（或者类似的东西，我忘记了确切的术语...）
b.你不能从UI线程执行逻辑操作，使用asynctask在后台处理数据库查询..

至于第二个我确信95%，因为我曾经遇到过类似的问题并且（使用asynctask）解决了我的问题