我在博客或 SO 上找到了这个示例数据库代码（不记得了）
package com.learn.db;
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;
public class DBAdapter {
private static final String DATABASE_NAME = " nba";
private static final String DATABASE_TABLE = "bookList";
private static final int DATABASE_VERSION = 1;
private static String TAG = "Upgrading Database!";
public static final String KEY_BOOK = "book";
public static final String KEY_AUTHOR = "author";
public static final String KEY_ISBN = "isbn";
public static final String KEY_ROWID = "_id";
public static final String KEY_RATING = "rating";
public static final String KEY_STATUS = "status";
private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;
private static final String DATABASE_CREATE = " create table "
+ DATABASE_TABLE + " (" + KEY_ROWID
+ " integer primary key autoincrement, " + KEY_AUTHOR
+ " text not null, " + KEY_BOOK + " text not null, " + KEY_RATING
+ " text not null, " + KEY_STATUS + " text not null, " + KEY_ISBN
+ " text not null); ";
private final Context mCtx;
public DBAdapter(Context ctx) {
this.mCtx = ctx;
}
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) {
db.execSQL("ALTER TABLE bookList ADD COLUMN String status");
}
}
public DBAdapter open() throws SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}
public void close() {
mDbHelper.close();
}
public long createBook(String book, String author, String isbn,
float rating, String status) {
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_BOOK, book);
initialValues.put(KEY_AUTHOR, author);
initialValues.put(KEY_ISBN, isbn);
initialValues.put(KEY_RATING, rating);
initialValues.put(KEY_STATUS, status);
return mDb.insert(DATABASE_TABLE, null, initialValues);
}
public boolean deleteBook(long rowId) {
return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}
public Cursor fetchAllBooks() {
return mDb.query(DATABASE_TABLE, new String[] { KEY_BOOK, KEY_ISBN,
KEY_AUTHOR, KEY_ROWID, KEY_RATING, KEY_STATUS }, null, null,
null, null, null);
}
public Cursor fetchBook(long rowId) throws SQLException {
Cursor mCursor = mDb.query(DATABASE_TABLE, new String[] { KEY_BOOK,
KEY_AUTHOR, KEY_ROWID, KEY_ISBN, KEY_RATING, KEY_STATUS },
KEY_ROWID + "=" + rowId, null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
public boolean updateBook(long rowId, String book, String author,
String isbn, float rating, String status) {
ContentValues args = new ContentValues();
args.put(KEY_BOOK, book);
args.put(KEY_AUTHOR, author);
args.put(KEY_ISBN, isbn);
args.put(KEY_RATING, rating);
args.put(KEY_STATUS, status);
return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}
我试图在我的主要活动中添加一条记录，但我在添加新书的那一行的 logcat 中遇到错误。
package com.learn.db;
import java.util.Random;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
public class Start extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.start);
DBAdapter fish_db = new DBAdapter(getApplicationContext());
fish_db.createBook("Captain Underpants", "Dav Pilkey", "12343251321", 5, "In stock");
Cursor cursor = fish_db.fetchAllBooks();
if (cursor.moveToFirst()){
do{
String data = cursor.getString(cursor.getColumnIndex("data"));
Toast.makeText(getApplicationContext(), data, Toast.LENGTH_LONG).show();
}while(cursor.moveToNext());
}
cursor.close();
}
}
根据logcat的实际错误是在线的空指针return mDb.insert(DATABASE_TABLE, null, initialValues);
有任何想法吗？