AndroidSQLite数据库连接实现登录功能

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public class MainActivity extends AppCompatActivity implements View.OnClickListener{
  //访问数据库的类
  SQLiteDatabase db;

  //定义常量，作为消息的key
  public final static String MESSAGE_KEY="com.android2";

 @Override
  protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    /**
     * (参数)1、context MainActivity
     * 2、name 数据库名
     * 3、
     * 4、版本号
     */
    final DatabaseHelper databaseHelper = new DatabaseHelper(this,"emis.db",null,2);

    //获得读取数据库权限
    db = databaseHelper.getReadableDatabase();
    setContentView(R.layout.activity_main);
  }
  /*响应*/
  private void userLogin() {
    EditText et1 = findViewById(R.id.username);
    String username = et1.getText().toString();
    EditText et2 = findViewById(R.id.password);
    String password = et2.getText().toString();

    //游标类Cursor 负责生成读写数据库的对象
    Cursor cursor = db.rawQuery("SELECT * FROM users WHERE username=&＃63; AND password=&＃63;",new String[]{username,password});

    //数据库中有此数据，登录成功
    if(cursor.getCount()>0){
      Intent intent = new Intent(this,ReceiveActivity.class);
      intent.putExtra(MESSAGE_KEY,username);
      startActivity(intent);
    }
    else{
      Toast.makeText(MainActivity.this,"用户名或密码错误!",Toast.LENGTH_SHORT).show();
    }


  }
}

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package com.android02;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class ReceiveActivity extends AppCompatActivity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_receive);

    //获取intent引用
    Intent intent = getIntent();

    //以MESSAGE_KEY获取获取编辑框文字
    String message = intent.getStringExtra(MainActivity.MESSAGE_KEY);

    //以id获取TextView
    TextView textView = findViewById(R.id.output);

    //显示message
    textView.setText("欢迎!"+message);


  }
}