游标或原始查询崩溃，

Question

我是安卓编程的新手。我正在尝试创建一个数据库一个表，但它崩溃了：

import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase;
public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "db";
    public static final String CREATE_ITEMS_TABLE = "CREATE TABLE items ( _ID INTEGER PRIMARY KEY, code INTEGER," +     "item  TEXT,  description TEXT);";
    private static final String put = "insert into items (code,item,description) values (1,obj,obj info)";
    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_ITEMS_TABLE);
        db.execSQL(put);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        android.util.Log.w("Constants", "Upgrading database, which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS constants");
        onCreate(db);
    }
}
Cursor c;
DatabaseHelper db = new DatabaseHelper(this);
c = db.getReadableDatabase().rawQuery("SELECT * FROM items ORDER BY code;", null);
if(c.moveToFirst()){
     String code= c.getString(1); 
     String item= c.getString(2);
     String info= c.getString(3);
}

结果我只正确处理了第一个字段，第二个字段是字段名称，第三个字段使程序崩溃。

Answer 1

所以，这里有一个建议，应该对你来说效果更好一点。我刚刚测试了它是否有效，它可以在不崩溃的情况下执行，并提供一点输出来验证数据。

我把它分成两个文件，这只是个人风味。

首先，您的数据库助手类

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
 * Created by shellstrom on 2017-05-29.
 */
public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "db";
    public static final String CREATE_ITEMS_TABLE = "CREATE TABLE items (_ID INTEGER PRIMARY KEY, code INTEGER, item TEXT, description TEXT)";
    private static final String put = "INSERT INTO items (code,item,description) values ('','1', 'obj', 'obj info')";
    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_ITEMS_TABLE);
        db.execSQL(put);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        android.util.Log.w("Constants", "Upgrading database, which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS items");
        onCreate(db);
    }
}

然后我从中运行程序的 MainActivity 类：

import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Cursor c;
        DatabaseHelper db = new DatabaseHelper(this);
        c = db.getReadableDatabase().rawQuery("SELECT * FROM items ORDER BY code", null);
        Log.d("TAG", "c count" +c.getCount());
        if(c.moveToFirst()){
            String code= c.getString(1);
            String item= c.getString(2);
            String info= c.getString(3);
            Log.d("TAG", "c1: " +code+ " c2: " +item+ " c3: " +info);
        }
    }
}

现在，我没有花任何时间来解决其他问题，例如进行参数化查询、错误处理等。我只是想至少给你一些基于你的样本编译和运行的东西。如果您有任何疑问，请随时提问。