Android SQLite-无法在onCreate之外调用数据库处理程序 [英] Android Sqlite - unable to call database handler outside of onCreate
问题描述
所以这是代码:
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")));通过loginSuccess方法.
Now I'm sure the issue is because I'm calling db.addUser(new User(1, "name", "email","password","van","username")); from the loginSuccess method.
如何使这个简单的插入件起作用?我敢肯定这个问题与上下文有关.我没有运气尝试过在Android上获取上下文"的静态方法吗?
How can I get this simple insert to work? I'm sure the issue is soemthing to do with contexts. I've tried this with no luck Static way to get 'Context' on Android?
谢谢！
推荐答案
尝试使用单例设计模式访问数据. 检查此发布以了解操作方法.
Try using a singleton design pattern to access the data. Check this post out to see how.
据我所知，loginSuccess()是在从Web服务器接收数据后被调用的.
As far as I can see loginSuccess() is called after receiving data from a web server.
您的应用程序可能试图同时将数据写入数据库.
It is probable that your app is trying to write data to the database simultaneously.
当使用DatabaseHandlerV2的多个实例时，请考虑关闭连接.
When using multiple instances of DatabaseHandlerV2 consider closing the connection.
示例:
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();
}
您会注意到与数据库的连接未关闭.
使用单例模式时，我们仅使用SampleHelper的一个实例，因此我们可以保持连接打开.
As you can notice the connection to the database is not closed.
When using a singleton pattern we use only one instance of SampleHelper so we can keep the connection opened.
直到现在我才检查您的更新日志.它说:
I did not check your updated log untill now. It says:
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.
That means your did not close the connection(db.close();), thus the null pointer exception when executing this.getReadableDatabase(); on deleteTableData() method.
我仍然建议使用提供的示例代码来避免数据库被锁定的异常.
I still recommend using the sample code provided to avoid database is locked exceptions.
对于openOrCreateDatabase异常，请检查此帖子.请注意，数据库名称以.db结尾.还要检查您的上下文是否为空.
For openOrCreateDatabase exception check this post. Notice that the database name ends with .db. Also check if your context is null or not.
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