Question

目的是从停车场表格栏中检索停车场名称＆＃39; CPNAME＆＃39;并将这些名称行放在另一个班级中。旋转器将显示的arraylist。说实话，我甚至不确定这种方式是否会显示微调器中的行......

目前的问题是，当我进入spinner访问调用getCpnames（）的arraylist的活动时。我真的无法解决我的代码的哪一部分正在对数据库进行其他调用以锁定它而不是getCpnames（）。感谢您提前获得帮助，我对编程很陌生。

错误讯息：

Caused by: java.lang.NullPointerException
at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:256)
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
atandroid.database.sqlite.SQLiteOpenHelper.getWritableDatabase
(SQLiteOpenHelper.java:164)
at com.example.parkangel.DbHelper.getCpnames(DbHelper.java:74)
at com.example.parkangel.BookTicket.<init>(BookTicket.java:19)

* 我的数据库类代码：*

package com.example.parkangel;

import java.util.ArrayList;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DbHelper extends SQLiteOpenHelper
{
private DbHelper dbHelper;
private Context ourContext;
private static DbHelper instance;
private SQLiteDatabase ourDatabase;

private static final String DATABASE_NAME = "CPDB.db";
private static final String DATABASE_TABLE = "CPTable";
private static final int DATABASE_VERSION = 1;

public static final String KEY_ID = "_id";
public static final String KEY_CPNAME = "cpname";
public static final String KEY_COST = "cost";

    public DbHelper(Context context)
    {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        // TODO Auto-generated constructor stub 
    }

    public static DbHelper getInstance(Context context)
    {
        if (instance == null)
        {
            instance = new DbHelper(context);   
        }
        return instance;
    }

    @Override
    public void onCreate(SQLiteDatabase db) 
    {
        // TODO Auto-generated method stub
        db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" +
                KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                KEY_CPNAME + " TEXT NOT NULL, " + KEY_COST + " TEXT 
                                    NOT NULL);");

        db.execSQL("INSERT INTO " + DATABASE_TABLE + " Values ('1','Learning 
                    Resource Center','2');");
        db.execSQL("INSERT INTO " + DATABASE_TABLE + " Values ('2','Park and 
                    Ride','1');");
        db.execSQL("INSERT INTO " + DATABASE_TABLE + " Values ('3','de 
                    Havilland Campus','2');");
        db.execSQL("INSERT INTO " + DATABASE_TABLE + " Values ('4','Multi 
                    Storey Building','2');");
        db.execSQL("INSERT INTO " + DATABASE_TABLE + " Values 
                    ('5','Reception','2');");   
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    {
        // TODO Auto-generated method stub
        db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
        onCreate(db);
    }

    public synchronized DbHelper open() throws SQLException
    {
        System.out.println ("running open");
        if(ourDatabase == null || !ourDatabase.isOpen())
        ourDatabase = getWritableDatabase();
        return this;
    }   

    public String[] getCpnames()
    {
        if(ourDatabase == null || !ourDatabase.isOpen())
        ourDatabase = getWritableDatabase();
        String[] columns = new String[] {KEY_ID, KEY_CPNAME, KEY_COST};
        Cursor  c = ourDatabase.query(DATABASE_TABLE, columns, KEY_CPNAME,     
                    null, null, null, null);
        ArrayList<String> list = new ArrayList<String>();

        if (c != null)
        {
            c.moveToFirst();
            do
            {
                list.add(c.getString(0));
            }           
            while (c.moveToNext());
        }
        if (ourDatabase == null) System.out.println ("is null");

        return list.toArray(new String[]{});
    }   
}

这是一个活动类，其中araylist将存储检索到的行的行：

package com.example.parkangel;

import android.app.Activity;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;

public class BookTicket extends Activity implements OnClickListener{

Spinner spinner, spinner2;
String[] carParks = DbHelper.getInstance(this).getCpnames();

SQLite数据库被锁定; getDatabaseLocked（）

0 个答案: