Question

我最近做了一些小改动，似乎无法看到导致所有这一切的错误。非常感谢任何帮助

主要

package com.androidhive.androidsqlite;

import java.util.List;


import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;


public class AndroidAss2SQL extends Activity {
    /** Called when the activity is first created. */
    TextView text;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        DatabaseHandler db = new DatabaseHandler(this);

        /**
         * CRUD Operations
         * */
        // Inserting Contacts
        Log.d("Insert: ", "Inserting ..");
        db.addContact(new Coms("Gold", "100.00", "0"));
      db.addContact(new Coms("Silver", "300.00", "3"));
      db.addContact(new Coms("Wheat", "500.00", "4"));
      db.addContact(new Coms("Sugar", "750.00", "0"));
      db.addContact(new Coms("Coffee", "433.00", "9"));


        // Reading all contacts
        Log.d("Reading: ", "Reading all coms..");
        List<Coms> contacts = db.getAllContacts();       

        for (Coms cn : contacts) {
            String log = "Id: "+cn.getID()+" ,Name: " + cn.getName() + " ,Phone: " + cn.getPhoneNumber() + " ,Quantity: " + cn.getQuan();
                // Writing Contacts to log
        Log.d("Name: ", log);

        }



        Coms rando = db.getContact(1);
        text = (TextView) findViewById(R.id.textView2);
        text.setText(String.valueOf(rando));

        Coms rando1 = db.getContact(2);
        text = (TextView) findViewById(R.id.textView4);
        text.setText(String.valueOf(rando1));


        Coms rando2 = db.getContact(3);
        text = (TextView) findViewById(R.id.textView6);
        text.setText(String.valueOf(rando2));

        Coms rando3 = db.getContact(4);
        text = (TextView) findViewById(R.id.textView8);
        text.setText(String.valueOf(rando3));

        Coms rando4 = db.getContact(5);
        text = (TextView) findViewById(R.id.textView10);
        text.setText(String.valueOf(rando4));



    }
}

Com Class

package com.androidhive.androidsqlite;

public class Coms {

    //private variables
    int _id;
    String _name;
    String _price;
    String _quan;

    // Empty constructor
    public Coms(){

    }
    // constructor
    public Coms(int id, String name, String price){
        this._id = id;
        this._name = name;
        this._price = price;
    }

    // constructor
    public Coms(String name, String price){
        this._name = name;
        this._price = price;
    }
    // constructor
        public Coms(String name){
            this._name = name;
        }
        public Coms(String name, String price, String quan){
            this._name = name;
            this._price = price;
            this._quan = quan;
        }
        public Coms(int id, String name, String price, String quan){
            this._id = id;
            this._name = name;
            this._price = price;
            this._quan = quan;
        }
    @Override
    public String toString(){
           return this._price;
        }
    // getting ID
    public int getID(){
        return this._id;
    }

    // setting id
    public void setID(int id){
        this._id = id;
    }

    // getting name
    public String getName(){
        return this._name;
    }

    // setting name
    public void setName(String name){
        this._name = name;
    }

    // getting phone number
    public String getPhoneNumber(){
        return this._price;
    }

    // setting phone number
    public void setPhoneNumber(String phone_number){
        this._price = phone_number;
    }
    // getting name
        public String getQuan(){
            return this._quan;
        }

        // setting name
        public void setQuan(String name){
            this._quan = name;
        }
}

DB Handler - 我的大部分更改都是在这里进行的，尝试添加Quantity（quan）

package com.androidhive.androidsqlite;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHandler extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "comstuff";

    // Contacts table name
    private static final String TABLE_CONTACTS = "coms";

    // Contacts Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_PRICE = "price";
    private static final String KEY_QUAN = "quantity";


    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
                + KEY_PRICE + " TEXT," + KEY_QUAN + " TEXT" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

        // Create tables again
        onCreate(db);
    }


    /**
     * All CRUD(Create, Read, Update, Delete) Operations
     */

    // Adding new contact
    void addContact(Coms contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName()); // Contact Name
        values.put(KEY_PRICE, contact.getPhoneNumber()); // Contact Phone
        values.put(KEY_QUAN, contact.getQuan()); // Contact Phone

        // Inserting Row
        db.insert(TABLE_CONTACTS, null, values);
        db.close(); // Closing database connection
    }

    // Getting single contact
    Coms getContact(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                KEY_NAME, KEY_PRICE, KEY_QUAN }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Coms contact = new Coms(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2), cursor.getString(3));
        // return contact
        return contact;
    }
    Coms getName(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_CONTACTS, new String[] {
                KEY_NAME, KEY_PRICE, KEY_QUAN }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Coms contact = new Coms(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2), cursor.getString(3));
        // return contact
        return contact;
    }

    // Getting All Contacts
    public List<Coms> getAllContacts() {
        List<Coms> contactList = new ArrayList<Coms>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Coms contact = new Coms();
                contact.setID(Integer.parseInt(cursor.getString(0)));
                contact.setName(cursor.getString(1));
                contact.setPhoneNumber(cursor.getString(2));
                //when this is changed from 2 to 3 it causes an error
                contact.setQuan(cursor.getString(3));
                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }

    // Updating single contact
    public int updateContact(Coms contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName());
        values.put(KEY_PRICE, contact.getPhoneNumber());
        values.put(KEY_QUAN, contact.getQuan());


        // updating row
        return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
    }

    // Deleting single contact
    public void deleteContact(Coms contact) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
        db.close();
    }


    // Getting contacts Count
    public int getContactsCount() {
        String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

        // return count
        return cursor.getCount();
    }

}

Answer 1

仅在第一次运行时创建数据库表。如果创建了数据库，则不会再次调用onCreate。因此，如果向表中添加新列并插入涉及新列的记录，则会出现错误清除数据或卸载您的应用程序，然后重新安装并运行在模拟器中，选中“擦除用户数据”。

不会向数据库||插入值不会跑

1 个答案: