每日总结 3.1

今天学习了登陆界面的操作。

学习了连接数据库的用户登录：

package com.example.clock.db;



import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import androidx.annotation.Nullable;

import com.example.clock.jiben.User;
import com.example.clock.jiben.User;

import java.util.ArrayList;

public class DatabaseHelper extends SQLiteOpenHelper {
    //创建一个数据库
    private SQLiteDatabase db;

    public DatabaseHelper(@Nullable Context context) {
        super(context, "db_test", null, 1);
        db = getReadableDatabase();
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        //在第一次创建数据库的时候，创建一些字段
        String sql = "create table user(_id integer, name varchar(50), password varchar(40))";
        db.execSQL(sql);//sql语句的执行函数
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //如果这个表中存在user,我们可以先把他去掉,然后重新创建
        String sql = "DROP TABLE IF EXISTS user";
        db.execSQL(sql);
        onCreate(db);
    }
    //为使项目结构更加紧凑，我们在此类中编写增删改查的函数,因为只有登录和注册界面,因此只涉及到写入数据库insert和query的操作
    public void insert(String name,String password ){
        db.execSQL("insert into user(name,password)VALUES(?,?)",new Object[]{name,password});
    }

    public ArrayList<User> getAllDATA(){//查询数据库
        ArrayList<User> list = new ArrayList<User>();
        //查询数据库中的数据,并将这些数据按照降序的情况排列
        Cursor cursor = db.query("user",null,null,null,null,null,"name DESC");
        while(cursor.moveToNext()){
            int index_name = cursor.getColumnIndex("name");
            int index_password = cursor.getColumnIndex("password");
            String name = cursor.getString(index_name);
            String password = cursor.getString(index_password);
            list.add(new User(name,password));
        }
        return list;
    }
}

package com.example.clock;


import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.example.clock.db.DatabaseHelper;
import com.example.clock.jiben.User;
import com.example.clock.jiben.User;

import java.util.ArrayList;

public class Login extends AppCompatActivity {

    private DatabaseHelper mSQLite;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        Button btn_login = findViewById(R.id.login);
        Button btn_register = findViewById(R.id.register);
        EditText ed_name = findViewById(R.id.userName);
        EditText ed_password = findViewById(R.id.userpassword);

        btn_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                String name = ed_name.getText().toString().trim();
                String password = ed_password.getText().toString().trim();

                ArrayList<User> data = mSQLite.getAllDATA();
                boolean flag = false;
                for(int i = 0; i < data.size(); i++){
                    User userdata = data.get(i);
                    if(name.equals(userdata.getName())&&password.equals(userdata.getPassword())){
                        flag = true;
                        break;
                    }else{
                        flag = false;
                    }
                }

                if(!TextUtils.isEmpty(name)&&!TextUtils.isEmpty(password)){
                    if(flag){
                        Intent intent1 = new Intent(Login.this, MainActivity.class);
                        startActivity(intent1);
                        finish();
                        Toast.makeText(Login.this, "登录成功", Toast.LENGTH_SHORT).show();
                    }
                    else{
                        Toast.makeText(Login.this, "用户名或密码不正确", Toast.LENGTH_SHORT).show();
                    }
                }
                else{
                    Toast.makeText(Login.this, "用户名与密码不能为空", Toast.LENGTH_SHORT).show();
                }
            }
        });

        btn_register.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent2 = new Intent(Login.this, Register.class);
                startActivity(intent2);
                finish();
            }
        });
        mSQLite = new DatabaseHelper(Login.this);
    }
}