Question

我有三个按钮来保存，加载和删除数据库中的数据。

TotalResults.java

package com.example.simplegame;

android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class TotalResults extends Activity {

DatabaseManager db = new DatabaseManager(this);
String name;
int score;
TextView result;
TextView saved;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_total_results);

    result = (TextView) findViewById (R.id.textResult);
    saved = (TextView) findViewById (R.id.textLoad);
    Button save = (Button) findViewById (R.id.buttonSave);
    Button load = (Button) findViewById (R.id.buttonLoad);

      Intent intent = getIntent();
      name = intent.getExtras().getString("name");
      score = intent.getExtras().getInt("score");

      result.setText("Name: "+name+" , Score: "+score );

      save.setOnClickListener(new OnClickListener(){

            public void onClick(View v) {

                db.addContact(new PlayerData(name,score));
                Log.d("Insert: ", "Inserting .."); 

            } 
      });



          load.setOnClickListener(new OnClickListener(){

                public void onClick(View v) {

                    String showName = db.getContact(0).getName();
                    int showScore = db.getContact(0).getscore();
                    saved.setText("Player Name: "+showName+" Player Score: "+showScore);

                } 
          });





}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.total_results, menu);
    return true;
}

}

和 DatabaseManager.java

package com.example.simplegame;

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 DatabaseManager 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 DatabaseManager(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
void addContact(PlayerData contact) {
    SQLiteDatabase db = this.getWritableDatabase();

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

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

// Getting single contact
PlayerData 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();

    PlayerData contact = new PlayerData(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1), cursor.getInt(2));

    cursor.close();
    // return contact
    return contact;
}

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

    // return contact list
    return contactList;
}

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

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

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

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

}

它插入数据但强制停止如果我单击加载按钮并且logcat说：

08-30 18:48:41.616: E/AndroidRuntime(760): android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
08-30 18:48:41.616: E/AndroidRuntime(760):  at com.example.simplegame.DatabaseManager.getContact(DatabaseManager.java:79)

请帮忙。提前谢谢！

Answer 1

Load只会获取id为0的元素，而不是数据库中的第一个条目。因此，如果您删除了数据库的第一个条目，这将始终失败。

您需要做的是从getAllContacts（）函数中获取第一个用户。在此之后，您可以在检查用户之后计算出用户详细信息。

List<PlayerData> contacts = db.getAllContacts();
//check to ensure there are users
if(contacts.size()==0) throw new Exception();
PlayerData player = contacts.get(0);
String showName = player.getName();
int showScore = player.getscore();

Answer 2

在使用光标检索数据之前，应始终检查光标。一种方法是检查cursor.isAfterLast()和cursor.isBeforeFirst()。

无法从数据库中获取数据

2 个答案: