Question

好的，所以我希望将数据库合并到我正在处理的应用程序项目中但是在这里遇到了问题...下面是数据库处理程序类的代码（取自androidhive.info我相信）< / p>

package apps.sqlitetest;

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 = "contactsManager";

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

// Contacts Table Columns names
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);
}

// 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_PH_NO + " 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
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

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

// Getting single contact
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;
}

// Getting All Contacts
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;
}

// Updating single contact
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()) });
}

// Deleting single contact
public void deleteContact(Contact 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();
}

}

所以，这似乎一切都很顺利......但是事情就是这样，我在MainActivity中有这一行试图通过在TextView中显示（单个）结果来测试数据库：

text.setText(db.getContact(9100).toString()) ;

我想我现在会提到Contact类也来自androidhive教程;只是一个简单的联系人表示（如电话中的条目），其中包含字段id（int），名称，电话号码（两个字符串）。主活动中有一组先前的行插入一些联系人，其中一行的ID为“9100”。但是，这个setText行似乎在logcat上抛出了以下错误，并因此在运行时停止了应用程序：

02-22 15:04:37.682: E/AndroidRuntime(847): java.lang.RuntimeException: 
Unable to start activity 
ComponentInfo{apps.sqlitetest/apps.sqlitetest.MainActivity}:    
android.database.CursorIndexOutOfBoundsException: 
Index 0 requested, with a size of 0
02-22 15:04:37.682: E/AndroidRuntime(847):  
at apps.sqlitetest.DatabaseHandler.getContact(DatabaseHandler.java:81)
02-22 15:04:37.682: E/AndroidRuntime(847):  
at apps.sqlitetest.MainActivity.onCreate(MainActivity.java:40)

有人可以告诉我这里有什么问题吗？

Answer 1

一个问题出在getContact()。您永远不会检查光标实际上是否包含任何数据。首先，删除此检查：

if (cursor != null)

cursor永远不会是null。

而是检查从cursor.moveToFirst()返回的结果。 false值表示游标为空。只有获得true结果时，才能继续阅读光标中的字段并构建联系人。

正确处理光标不包含数据的情况后，您可以设置查找查询未检索到预期数据的原因。

Android中简单的SQLite测试问题

1 个答案: