Android中簡單SQLite測試的問題

Question

好的，我正在尋找將數據庫合併到我正在處理的應用程序項目中，但這裏遇到了問題...下面是數據庫處理程序類的代碼（取自androidhive.info我相信）

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，這似乎是一個好主意好嗎......但這裏的東西，我有這條線在我的MainActivity試圖測試通過顯示（單）結果讀取數據庫在TextView中：

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

我想我現在要提的是Contact類是從t他也是androidhive教程;只是一個簡單的聯繫表示（如電話中的條目）與字段id（int），名稱，電話號碼（兩個字符串）。在主要活動中有一組前面的行插入一些聯繫人，其中一個具有ID「9100」。然而，這種的setText線似乎拋出了以下錯誤到logcat的，並因此停止應用程序時，它運行：

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) 

有人能告訴我什麼是錯在這裏嗎？

Answer 1

一個問題在getContact()。您從不檢查光標實際上是否包含任何數據。首先，刪除此檢查：

if (cursor != null) 

爲cursor永遠不能null。

而是檢查從cursor.moveToFirst()返回的結果。 A值爲false表示遊標爲空。只有當你得到true的結果時，你才應該繼續閱讀光標中的字段並建立聯繫人。

一旦正確處理光標不包含數據的情況，您可以設置查找爲什麼查詢不檢索預期數據。