Android Sqlite - 无法在 onCreate 之外调用数据库处理程序
Posted
技术标签:
【中文标题】Android Sqlite - 无法在 onCreate 之外调用数据库处理程序【英文标题】：Android Sqlite - unable to call database handler outside of onCreate 【发布时间】：2017-06-27 14:56:49 【问题描述】：代码如下：
主要活动：
package com.dummies.myapplication;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.sql.SQLClientInfoException;
import java.util.List;
import com.dummies.myapplication.User;
public class MainActivity extends AppCompatActivity
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//new LoginHelper().Process();
DatabaseHandlerV2 db = new DatabaseHandlerV2(this);
// db.deleteTable();
// /db.makeTable(DatabaseHandlerV2);
//Log.d("Insert: ", "Inserting ..");
db.addUser(new User(1, "name", "email","password","van","username"));
// Reading all contacts
Log.d("Reading: ", "Reading all contacts..");
List<User> users = db.getAllUsers();
for (User us : users)
String log = "Id: "+us.getID()+" ,Name: " + us.getName() + " ,email: " + us.getEmail() + " ,password: " + us.getPassword() + ",username:" + us.getUsername() + ",van:" + us.getVan();
// Writing Contacts to log
Log.d("Name: ", log);
Button login = (Button) findViewById(R.id.loginSubmit);
final EditText clientUsername = (EditText)findViewById(R.id.username);
final EditText clientPassword = (EditText)findViewById(R.id.password);
login.setOnClickListener(new View.OnClickListener()
public void onClick(View v)
//Log.d("User deets username", clientUsername.getText().toString());
//Log.d("User deets password", clientPassword.getText().toString());
String username = clientUsername.getText().toString();
String password = clientPassword.getText().toString();
LoginHelper LoginHelper = new LoginHelper();
LoginHelper.checkLogin(username, password);
);
//db.deleteTable();
public void loginSuccess(String id, String username, String email, String password, String vanId, String name)
//Log.d("logged in user", id + "," + username + "," + email + "," + password + "," + vanId);
// db.addUser(new User(id, username, email,password,vanId));
int intId = Integer.parseInt(id);
//int intVanId = Integer.parseInt(vanId);
DatabaseHandlerV2 db = new DatabaseHandlerV2(this);
db.deleteTableData();
// db.addUser(new User(intId, name, email,password,vanId,username));
db.addUser(new User(1, "name", "email","password","van","username"));
Log.d("Jon Error", "Logged in user is" + intId);
// db.deleteTable();
数据库助手 V2：
package com.dummies.myapplication;
/**
* Created by Jon on 05/02/2017.
*/
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.SQLiteDatabaseLockedException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DatabaseHandlerV2 extends SQLiteOpenHelper
// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "userManager";
// Contacts table name
private static final String TABLE_USERS= "users";
// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_EMAIL = "email";
private static final String KEY_PASSWORD = "password";
private static final String KEY_VAN = "van_id";
private static final String KEY_USERNAME = "username";
public DatabaseHandlerV2(Context context)
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// Creating Tables
@Override
public void onCreate(SQLiteDatabase db)
String CREATE_USERS_TABLE = "CREATE TABLE " + TABLE_USERS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
+ KEY_EMAIL + " TEXT" + "," + KEY_PASSWORD + " TEXT," + KEY_VAN + " INTEGER," + KEY_USERNAME + " TEXT" + ")";
db.execSQL(CREATE_USERS_TABLE);
Log.d("Jon error", "creating 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_USERS);
// Create tables again
onCreate(db);
/**
* All CRUD(Create, Read, Update, Delete) Operations
*/
// Adding new contact
void addUser(User user)
SQLiteDatabase db = this.getWritableDatabase();
//onCreate(db);
ContentValues values = new ContentValues();
values.put(KEY_NAME, user.getName()); // Contact Name
values.put(KEY_EMAIL, user.getEmail()); // Contact Email
values.put(KEY_PASSWORD, user.getPassword());
values.put(KEY_VAN, user.getVan());
values.put(KEY_USERNAME, user.getUsername());
// Inserting Row
db.insert(TABLE_USERS, null, values);
db.close(); // Closing database connection
// Getting single contact
Contact getUser(int id)
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_USERS, new String[] KEY_ID,
KEY_NAME, KEY_EMAIL, KEY_PASSWORD, KEY_VAN, KEY_USERNAME , KEY_ID + "=?",
new String[] String.valueOf(id) , null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
// return contact
return contact;
// Getting All Contacts
public List<User> getAllUsers()
Log.d("Jon Error", "debug");
List<User> userList = new ArrayList<User>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_USERS;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst())
do
Log.d("Jon Error:", "test");
User user = new User();
user.setID(Integer.parseInt(cursor.getString(0)));
//Log.d(cursor.getString(0));
user.setName(cursor.getString(1));
user.setEmail(cursor.getString(2));
user.setPassword(cursor.getString(3));
user.setVan(cursor.getString(4));
user.setUsername(cursor.getString(5));
// Adding contact to list
userList.add(user);
while (cursor.moveToNext());
// return contact list
return userList;
// Updating single contact
public int updateUser(User user)
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, user.getName());
values.put(KEY_EMAIL, user.getEmail());
values.put(KEY_PASSWORD, user.getPassword());
values.put(KEY_VAN, user.getVan());
values.put(KEY_VAN, user.getUsername());
// updating row
return db.update(TABLE_USERS, values, KEY_ID + " = ?",
new String[] String.valueOf(user.getID()) );
// Deleting single contact
public void deleteUser(Contact contact)
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_USERS, KEY_ID + " = ?",
new String[] String.valueOf(contact.getID()) );
db.close();
public void deleteTable()
SQLiteDatabase db = this.getReadableDatabase();
db.execSQL("DROP TABLE IF EXISTS " + TABLE_USERS);
Log.d("Jon error", "deleteing");
public void deleteTableData()
SQLiteDatabase db = this.getReadableDatabase();
db.execSQL("DELETE FROM " + TABLE_USERS);
// Getting contacts Count
public int getUsersCount()
String countQuery = "SELECT * FROM " + TABLE_USERS;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
// return count
return cursor.getCount();
现在我确定问题是因为我正在调用 db.addUser(new User(1, "name", "email","password","van","username"));来自 loginSuccess 方法。
我怎样才能让这个简单的插入工作？我确信这个问题与上下文有关。我试过这个没有运气Static way to get 'Context' on Android?
谢谢！
【问题讨论】：
您似乎是从任务中调用loginSuccess()。您的上下文为空。打开数据库时尝试使用全局应用程序上下文。
【参考方案1】：
尝试使用单例设计模式来访问数据。 看看这个post 看看如何。
据我所知，loginSuccess() 在从网络服务器接收数据后被调用。
您的应用可能正在尝试同时将数据写入数据库。
编辑： 当使用多个 DatabaseHandlerV2 实例时，请考虑关闭连接。
例子：
助手：
public class SampleHelper extends SQLiteOpenHelper
private static SampleHelper instance;
private static Context mContext;
public static synchronized SampleHelper getHelper(Context context)
if (instance == null)
instance = new SampleHelper(context);
return instance;
private SampleHelper(Context context)
super(context, DATABASE_NAME, null, DATABASE_VERSION);
mContext = context;
写作：
SampleHelper helper = SampleHelper.getHelper(mContext);
SQLiteDatabase writableDb = helper.getWritableDatabase();
String statement = "INSERT OR REPLACE INTO table_name(colA,colB) VALUES (valA,valB)";
writableDb.execSQL(statement);
阅读：
Cursor cursor = null;
try
cursor = SampleHelper.getHelper(mContext).getReadableDatabase().rawQuery("SELECT colA FROM table_name");
if (cursor.moveToFirst())
do
/**read the data here**/
while (cursor.moveToNext());
finally
if(null != cursor)
cursor.close();
如您所见，与数据库的连接并未关闭。
当使用单例模式时，我们只使用SampleHelper 的一个实例，因此我们可以保持连接打开。
直到现在我才检查您的更新日志。它说：
A SQLiteConnection object for database '/data/data/com.dummies.myapplication/databases/userManager' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
这意味着您没有关闭连接（db.close();），因此在deleteTableData() 方法上执行this.getReadableDatabase(); 时出现空指针异常。
我仍然建议使用提供的示例代码来避免数据库被锁定异常。
对于openOrCreateDatabase 异常，请检查此post。请注意，数据库名称以.db 结尾。还要检查你的上下文是否为空。
【讨论】：
你能提供一个具体的例子吗？ 当然。我就是这样做的。 谢谢。我仍然有一个错误使用你的代码。 - 查看更新的问题。 我已经更新了我的答案以解决新的异常。 我仍然遇到同样的错误，我相信这是因为在调用 DatabaseHaldler.getHelper 时，我将它作为不是有效上下文的 permiter 传递。有任何想法吗？ - 编辑 - 我尝试从 MainActivity 中的 onCreate 方法运行代码并且它很好 - 在 loginSuccess 上它失败了。【参考方案2】：每次你想改变它的结构时，你都必须打开一个可写的数据库（不可读）。所以，在你的 DatabaseHandlerV2 类中需要插入、删除或更新数据到数据库中的每个方法中，把这行：SQLiteDatabase db = this.getWritableDatabase(); 代替：SQLiteDatabase db = this.getReadableDatabase();。
在这种特定情况下，要解决此错误，您必须以这种方式更改deleteTableData() 方法：
public void deleteTableData()
SQLiteDatabase db = this.getWritableDatabase();
db.execSQL("DELETE FROM " + TABLE_USERS);
【讨论】：
我仍然收到错误：E/AndroidRuntime: FATAL EXCEPTION: main Process: com.dummies.myapplication, PID: 3861 java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite .SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' 在空对象引用上 这并不能解决问题，在大多数情况下，调用getWriteableDatabase() 与调用getReadableDatabase() 相同。
似乎“this”在“deleteTableData”方法中为空。那么您可以发布代码以显示您在哪里调用 loginSuccess 吗？【参考方案3】：
DatabaseHandlerV2 maindb=null;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
maindb= new DatabaseHandlerV2(this);
public void loginSuccess(String id, String username, String email, String password, String vanId, String name)
maindb.deleteTableData();
【讨论】：
以上是关于Android Sqlite - 无法在 onCreate 之外调用数据库处理程序的主要内容，如果未能解决你的问题，请参考以下文章
Android SQLite 更新无法在 AsyncTask 的后台运行