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我已经写了一个简单的SQLite R & L系统。但是我运行后遇到了问题 - 系统总是弹出一个敬酒“Ac不存在”，当我按下loginBtn时。如何在Android Studio中使用SQLite编写注册和登录系统？
这是代码： LoginActivity.java
package com.example;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
public class LoginActivity extends AppCompatActivity {
EditText usernameTxt, passwordTxt;
Button loginBtn, newAcBtn;
DatabaseHandler dbHelper;
List<UsersDatabase> Users = new ArrayList<UsersDatabase>();
public void define(){
usernameTxt = (EditText)findViewById(R.id.txtUsername);
passwordTxt = (EditText)findViewById(R.id.txtPassword);
loginBtn = (Button)findViewById(R.id.btnLogin);
newAcBtn = (Button)findViewById(R.id.btnNewAccount);
dbHelper = new DatabaseHandler(getApplicationContext());
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
define();
NewAccountBtnOnClick();
LoginBtnEnable();
LoginBtnOnClick();
}
public void NewAccountBtnOnClick(){
newAcBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent LoginToMain = new Intent(LoginActivity.this, MainActivity.class);
startActivity(LoginToMain);
}
});
}
public void LoginBtnEnable(){
usernameTxt.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i2, int i3) {
if (String.valueOf(usernameTxt.getText()).trim().length() > 0) {
passwordTxt.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i2, int i3) {
loginBtn.setEnabled(String.valueOf(passwordTxt.getText()).trim().length() > 0);
}
@Override
public void afterTextChanged(Editable s) {
}
});
}
}
@Override
public void afterTextChanged(Editable s) {
}
});
}
public void LoginBtnOnClick(){
loginBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
UsersDatabase user = new UsersDatabase(dbHelper.getUserCount(), String.valueOf(usernameTxt.getText()), String.valueOf(passwordTxt.getText()));
if (!userExists(user)) {
Toast.makeText(getApplicationContext(), " Ac does not exist.", Toast.LENGTH_SHORT).show();
return;
}
Intent LoginToMain = new Intent(LoginActivity.this, MainActivity.class);
startActivity(LoginToMain);
}
});
}
private boolean userExists(UsersDatabase user)
{
String name = user.getUsername();
int userCount = Users.size();
for (int i = 0; i < userCount; i++)
{
if (name.compareToIgnoreCase(Users.get(i).getUsername()) ==0)
return true;
}
return false;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_login, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
UsersDatabase.java
package com.example;
public class UsersDatabase {
private String _username, _password;
private int _uid;
public UsersDatabase(int uid, String username, String password)
{
_uid = uid;
_username = username;
_password = password;
}
public String getUsername()
{
return _username;
}
public int getUserId() { return _uid; }
public String getPassword()
{
return _password;
}
}
和DatabaseHandler.java
package com.example;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
import java.util.List;
public class DatabaseHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "usersManager",
TABLE_USERS = "Users",
KEY_UID = "uid",
KEY_USERNAME = "username",
KEY_PASSWORD = "password";
public DatabaseHandler(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL("CREATE TABLE " + TABLE_USERS + " (" + KEY_UID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_USERNAME + " TEXT," + KEY_PASSWORD + " TEXT)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_USERS);
onCreate(db);
}
public void createUser(UsersDatabase user)
{
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_USERNAME, user.getUsername());
values.put(KEY_PASSWORD, user.getPassword());
db.insert(TABLE_USERS, null, values);
db.close();
}
public UsersDatabase getUser(int id)
{
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.query(TABLE_USERS, new String[] { KEY_UID, KEY_USERNAME, KEY_PASSWORD}, KEY_UID + "=?", new String[] { String.valueOf(id)},null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
UsersDatabase user = new UsersDatabase(Integer.parseInt(cursor.getString(0)),cursor.getString(1), cursor.getString(2));
db.close();
cursor.close();
return user;
}
public void deleteUser(UsersDatabase user)
{
SQLiteDatabase db = getWritableDatabase();
db.delete(TABLE_USERS, KEY_UID + "=?", new String[] { String.valueOf(user.getUserId())});
db.close();
}
public int getUserCount()
{
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM " + TABLE_USERS, null);
int count = cursor.getCount();
db.close();
cursor.close();
return count;
}
public int updateUser(UsersDatabase user)
{
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_USERNAME, user.getUsername());
values.put(KEY_PASSWORD, user.getPassword());
int rowsAffected = db.update(TABLE_USERS, values, KEY_UID + "=?", new String[]{String.valueOf(user.getUserId())});
db.close();
return rowsAffected;
}
public List<UsersDatabase> getAllUsers()
{
List<UsersDatabase> users = new ArrayList<UsersDatabase>();
SQLiteDatabase db = getWritableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM " + TABLE_USERS, null);
if (cursor.moveToFirst()) {
do {
users.add(new UsersDatabase(Integer.parseInt(cursor.getString(0)),cursor.getString(1), cursor.getString(2)));
}
while (cursor.moveToNext());
}
cursor.close();
db.close();
return users;
}
}