Question

我正在尝试使用onUpgrade()添加新表。我已经给出了查询来创建一个表，如果oldVersion小于newVersion，则执行该表。我增加了数据库版本，但我NullPointerException db.execSQL() onUpgrade() db onUpgrade()。

我检查调试模式并看到NullPointerException中的newVersion（我的代码中为i2）仍为7（见代码），但我改为8.

为什么我在db onUpgrade()获得SQLiteDatabase db {。}}。我已将onCreate()中this.db = db的值定义为onCreate(SQLiteDatabase db,..)（我从方法onUpgrade获得的值），并且我在构造函数中调用了SQLiteOpenHelper类扩展public class DatabaseHelper extends SQLiteOpenHelper { private static final int DATABASE_VERSION = 9; private static final String DATABASE_NAME = "database"; SQLiteDatabase db; ArrayList<String> arrayList; Context cont; DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); this.cont = context; arrayList = new ArrayList<>(); db = this.getWritableDatabase(); this.onUpgrade(db, 7, 8); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("create table tableName(name text,email text primary key,password varchar,phno int)"); db.execSQL("create table bookingDetails(email text, date text, time text,vehicle text,fromLocation text,destination text)"); db.execSQL("create table emptyTable (name text)"); db.execSQL("insert into emptyTable values(ad)"); this.db = db; } public boolean save(String name, String email, String password, String phno) { db = this.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("name", name); values.put("email", email); values.put("password", password); values.put("phno", phno); long rows; rows = db.insert("tableName", null, values); if (rows <= 0) { Toast.makeText(cont, "Failed", Toast.LENGTH_LONG).show(); return false; } return true; } public String getUserName(String email) { Cursor c = db.rawQuery("select name from tableName where email = '" + email + "'", null); c.moveToFirst(); return c.getString(0); } public void saveBookingDetails(String email, String date, String time, String vehicleType, String fromLocation, String destination) { db = this.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("email", email); values.put("date", date); values.put("time", time); values.put("vehicle", vehicleType); values.put("fromLocation", fromLocation); values.put("destination", destination); long rows; rows = db.insert("bookingDetails", null, values); if (rows <= 0) { Toast.makeText(cont, "Failed", Toast.LENGTH_LONG).show(); } else Toast.makeText(cont, "Saved", Toast.LENGTH_LONG).show(); } public void delete() { db.execSQL("delete from bookingDetails"); } public ArrayList displayUserDetails(String email) { int i = 0; Cursor cursor = db.rawQuery("select name,email,phno from tableName where email = '" + email + "'", null); cursor.moveToFirst(); do { arrayList.add(cursor.getString(cursor.getColumnIndex("name"))); arrayList.add(cursor.getString(cursor.getColumnIndex("email"))); arrayList.add(cursor.getString(cursor.getColumnIndex("phno"))); i++; } while (cursor.moveToNext()); return arrayList; } public boolean getLogin(String email, String pass) { db = this.getReadableDatabase(); Cursor cursor = db.rawQuery("select password from tableName where email = '" + email + "'", null); if (cursor.moveToFirst() && cursor.getCount() > 0 && cursor != null) { if (cursor.getString(0).equals((pass))) { return true; } } return false; } public long getTaskCount() { return DatabaseUtils.queryNumEntries(getReadableDatabase(), "tableName"); } public ArrayList getBookingHistory(String email) { ArrayList bookingHistoryList = new ArrayList(); String e = email; Cursor c = db.rawQuery("select * from bookingDetails where email = '" + email + "'", null); int cou = c.getCount(); c.moveToFirst(); do { bookingHistoryList.add(c.getString(c.getColumnIndex("date"))); bookingHistoryList.add(c.getString(c.getColumnIndex("time"))); bookingHistoryList.add(c.getString(c.getColumnIndex("fromLocation"))); bookingHistoryList.add(c.getString(c.getColumnIndex("destination"))); bookingHistoryList.add(c.getString(c.getColumnIndex("vehicle"))); } while (c.moveToNext()); return bookingHistoryList; } public ArrayList getTextViewText() { ArrayList txtViewList = new ArrayList(); Cursor cursor = db.rawQuery("select * from tableName", null); cursor.moveToFirst(); do { txtViewList.add(cursor.getString(cursor.getColumnIndex("name"))); txtViewList.add(cursor.getString(cursor.getColumnIndex("email"))); txtViewList.add(cursor.getString(cursor.getColumnIndex("phno"))); } while (cursor.moveToNext()); return txtViewList; } public void saveOnEdit(String email, String name, String phno, String password) { ContentValues values = new ContentValues(); if (name.length() == 0) { if (phno.length() == 0) { values.put("password", password); db.update("tableName", values, "email = '" + email + "'", null); } else if (password.length() == 0) { values.put("phno", phno); db.update("tableName", values, "email = '" + email + "'", null); } else { values.put("phno", phno); values.put("password", password); } } else if (password.length() == 0 && phno.length() == 0) { values.put("name", name); db.update("tableName", values, "email = '" + email + "'", null); } else if (password.length() == 0) { values.put("name", name); values.put("phno", phno); db.update("tableName", values, "email = '" + email + "'", null); } else if (phno.length() == 0) { values.put("name", name); values.put("password", password); db.update("tableName", values, "email = '" + email + "'", null); } else { values.put("name", name); values.put("password", password); values.put("phno", phno); db.update("tableName", values, "email = '" + email + "'", null); } } public String empty() { Cursor c = db.rawQuery("select name from emptyTable", null); return c.getString(c.getColumnIndex("name")); } @Override public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i2) { if (i < i2) { db.execSQL("create table emptyTable(name text)"); ContentValues values = new ContentValues(); values.put("name", "ad"); db.insert("emptyTable", null, values); } } @Override public void onConfigure(SQLiteDatabase db) { super.onConfigure(db); } @Override public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) { super.onDowngrade(db, oldVersion, newVersion); } @Override public void onOpen(SQLiteDatabase db) { super.onOpen(db); } }并将oldVersion和newVersion值传递给它。对不起，如果我试图解释太多让你困惑。我是android的新手，不知道这是否是向现有数据库添加新表的正确方法。

以下是代码：

DatabaseHelper.class

$.ajax({
        url: "https://localhost:8443/v1/accounts",
        type: 'GET',
        dataType: 'jsonp',
        beforeSend: function (xhr) {
            xhr.setRequestHeader('Authorization', 'Basic bHVpZ2lAZ21haWwuY29tOmFiYzEyMzQ1');
        }
    })

Answer 1

在onUpgrade中您使用了错误的引用：

    db.execSQL("create table emptyTable(name text)");

而不是

    sqLiteDatabase.execSQL("create table emptyTable(name text)");

您的构造函数将调用升级并在之前创建获取数据库引用，因此在升级时它仍然为null。

Answer 2

当数据库版本增加时您必须通过onCreate这样调用onUpgrade来呼叫@Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { onCreate(db); }：

assert req['status'] == 0

即使数据库版本增加，也不会调用onCreate（）

2 个答案: