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我想用 SQLite 数据库构建一个 Android 应用程序。我有两个 Java 类。第一个是 Contact 类，第二个是 DatabaseHandle 类，用于添加、更新等操作...

我没有收到错误，但如果我启动我的应用程序，我会变成这条消息......

在此处输入图像描述

这是我的联系课程

package de.linde.sqlite;

public class Contact {

    int _id;
    String _name;
    String _phone_number;

    public Contact(){}

    public Contact(int id,String name,String _phone_number){

        this._id = id; 
        this._name = name; 
        this._phone_number = _phone_number;
    }

    public Contact(String name,String _phone_number){

        this._name = name;
        this._phone_number = _phone_number; 
    }

    public int getID(){

        return this._id; 
    }

    public void setID(int id){

        this._id = id; 
    }

    public String getName(){

        return this._name; 
    }

    public void setName(String name){

        this._name = name; 
    }

    public String getPhoneNumber(){

        return this._phone_number;
    }

    public void setPhoneNumber(String phone_number){

        this._phone_number = phone_number; 
    }
}

这是我的DatabaseHandler类

package de.linde.sqlite;

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 {

    //Datenbank version
    private static final int DATABASE_VERSION = 1; 
    //Datenbankname
    private static final String DATABASE_NAME = "contactsManager";
    //Tabellenname
    private static final String TABLE_CONTACTS = "contacts";
    //Tabellenspalten
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_PH_NO = "phone_number";

    public DatabaseHandler(Context context){

        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    public void onCreate(SQLiteDatabase db){

        String CREATE_CONTACTS_TABLE = "CREATE TABLE" + TABLE_CONTACTS + "("
                                        + KEY_ID + "INTEGER PRIMARY KEY," + KEY_NAME + "TEXT," 
                                        + KEY_PH_NO + " TEXT" + ")";

        db.execSQL(CREATE_CONTACTS_TABLE); 
    }

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){

        db.execSQL("DROP TABLE IF EXISTS" + TABLE_CONTACTS); 

        onCreate(db); 
    }

    public void addContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName()); // Contact Name
        values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone Number

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

    public Contact getContact(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

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

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

    public List<Contact> getAllContacts() {
        List<Contact> contactList = new ArrayList<Contact>();
        // 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 {
                Contact contact = new Contact();
                contact.setID(Integer.parseInt(cursor.getString(0)));
                contact.setName(cursor.getString(1));
                contact.setPhoneNumber(cursor.getString(2));
                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }

    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();
    }

    public int updateContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName());
        values.put(KEY_PH_NO, contact.getPhoneNumber());

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

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


}

这是我的 MainActivity

package de.linde.sqlite;

import java.util.List;

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

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        DatabaseHandler db = new DatabaseHandler(this);

        Log.d("Insert: ", "Inserting .."); 
        db.addContact(new Contact("Wladimir","024324324"));
        db.addContact(new Contact("Max","0324324324"));
        db.addContact(new Contact("Benny","0324324"));
        db.addContact(new Contact("derSchwarze","051324324"));

        Log.d("Reading: ","Reading all Contacts..");
        List<Contact> contacts = db.getAllContacts();

        for (Contact cn : contacts) {

            String log = "Id: " + cn.getID() + " ,Name: " + cn.getName() + " ,Phone: " + cn.getPhoneNumber();
            Log.d("Name: ", log); 
        }
    }

}

我的activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >



</RelativeLayout>

我做错了什么:(

4

1 回答 1

3

CREATE_CONTACTS_TABLE在添加的值和连接的字符串之间添加空格，以便构建有效的表创建字符串：

"CREATE TABLE " + TABLE_CONTACTS + " (" + KEY_ID + " INTEGER PRIMARY KEY, " + KEY_NAME + " TEXT, " + KEY_PH_NO + " TEXT)";

您需要从手机/模拟器中卸载该应用程序，然后再次运行它以重新创建数据库。

同样的事情对 onUpgrade 方法中的 String 也是有效的：

"DROP TABLE IF EXISTS " + TABLE_CONTACTS
于 2012-10-11T12:22:16.140 回答