Android sqlite数据库空指针异常

Question

当我尝试将数据插入我的Android应用程序中的sqlite数据库时，出现了空指针异常。 我看了看代码，一切似乎都井井有条，而我为什么会收到空指针异常感到困惑。 代码如下：

import java.sql.Blob;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;


public class DBAdapter {

    public static final String KEY_ROWID = "id";
    public static final String KEY_STUDENTNAME = "studentname";
    public static final String KEY_DOB = "dob";
    public static final String KEY_ADDRESS1 = "address1";
    public static final String KEY_ADDRESS2 = "address2";
    public static final String KEY_TOWN = "town";
    public static final String KEY_POSTCODE = "postcode";
    public static final String KEY_PHONE = "phone";  
    public static final String KEY_STUDENT_PIC = "studentpic";  

    private static final String TAG = "DBAdapter"; 



    private static final String DATABASE_NAME = "studentDB3";
    private static final String DATABASE_TABLE = "tblstudents";
    private static final int DATABASE_VERSION = 1;

    private static final String DATABASE_CREATE =
        "create table tblstudents (id integer primary key autoincrement, "
        + "studentname text not null, dob text not null, " 
        + "address1 text not null, address2 text not null, "
        + "town text not null, postcode text not null, "
        + " phone text not null, studentpic blob);";

    private final Context context; 

    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public DBAdapter(Context ctx) 
    {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper 
    {
        DatabaseHelper(Context context) 
        {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) 
        {
            db.execSQL(DATABASE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, 
        int newVersion) 
        {
            Log.w(TAG, "Upgrading database from version " + oldVersion 
                    + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS tblStudents");
            onCreate(db);
        }
    }    

    //---opens the database---
    public DBAdapter open() throws SQLException 
    {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    //---closes the database---    
    public void close() 
    {
        DBHelper.close();
    }

    //---insert a title into the database---
    public long insertStudent(String studentname, String dob, String address1, String address2, String town, String postcode, String phone, byte[] studentpic) 
    {
        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_STUDENTNAME, studentname);
        initialValues.put(KEY_DOB, dob);
        initialValues.put(KEY_ADDRESS1, address1);
        initialValues.put(KEY_ADDRESS2, address2);
        initialValues.put(KEY_TOWN, town);
        initialValues.put(KEY_POSTCODE, postcode);
        initialValues.put(KEY_PHONE, phone);
        initialValues.put(KEY_STUDENT_PIC, studentpic);

        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    //---deletes a particular title---
    public boolean deleteTitle(long rowId) 
    {
        return db.delete(DATABASE_TABLE, KEY_ROWID + 
                "=" + rowId, null) > 0;
    }

    //---retrieves all the titles---
    public Cursor getAllStudents() 
    {
        return db.query(DATABASE_TABLE, new String[] {
                KEY_ROWID, 
                KEY_STUDENTNAME,
                KEY_DOB,
                KEY_ADDRESS1,
                KEY_ADDRESS2,
                KEY_TOWN,
                KEY_POSTCODE,
                KEY_PHONE,
                KEY_STUDENT_PIC
                            }, 
                null, 
                null, 
                null, 
                null, 
                null);
    }

    //---retrieves a particular title---
    public Cursor getStudent(long rowId) throws SQLException 
    {
        Cursor mCursor =
                db.query(true, DATABASE_TABLE, new String[] {
                        KEY_ROWID, 
                        KEY_STUDENTNAME,
                        KEY_DOB,
                        KEY_ADDRESS1,
                        KEY_ADDRESS2,
                        KEY_TOWN,
                        KEY_POSTCODE,
                        KEY_PHONE,
                        KEY_STUDENT_PIC
                        }, 
                        KEY_ROWID + "=" + rowId, 
                        null,
                        null, 
                        null, 
                        null, 
                        null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //---updates a student---
    public boolean updateStudent(long rowId, String studentname, 
    String dob, String address1, String address2, String town,
    String postcode, String phone, byte[] studentpic) 
    {
        ContentValues args = new ContentValues();
        args.put(KEY_STUDENTNAME, studentname);
        args.put(KEY_DOB, dob);
        args.put(KEY_ADDRESS1, address1);
        args.put(KEY_ADDRESS2, address2);
        args.put(KEY_TOWN, town);
        args.put(KEY_POSTCODE, postcode);
        args.put(KEY_PHONE, phone);
        args.put(KEY_STUDENT_PIC, studentpic);

        return db.update(DATABASE_TABLE, args, 
                         KEY_ROWID + "=" + rowId, null) > 0;
    }




}

---

Answer 1

在Android中，ID列应为_id ，而不是您设置的id ：

public static final String KEY_ROWID = "id";

可能值得一看。