android登录注册界面，数据存到数据库，实现数据库的增删改查功能

1. 建一个数据库文件

MyHelper

package com.example.test3;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

public class MyHelper extends SQLiteOpenHelper {
    public MyHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    /*public MyHelper(@Nullable Context context, @Nullable String name) {
        super(context, name, null, 1);
    }

    public MyHelper(@Nullable Context context) {
        super(context, "user.db", null, 1);
    }*/

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        String sql = "create table user(_id integer primary key autoincrement,username text,password text)";
        sqLiteDatabase.execSQL(sql);//执行上述sql语句建表过程

    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

1. 创建登录注册界面，功能界面（简化界面，全部在一个界面）

activity_sqlite_demo

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SQLiteDemoActivity">


    <ImageView
        android:id="@+id/sql_im1"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/teal_700"></ImageView>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="USER"
        android:textSize="30sp"
        android:textColor="#fff"
        android:layout_centerHorizontal="true"></TextView>

    <EditText
        android:id="@+id/sql_et1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:hint="用户名"
        android:layout_marginTop="10dp"
        android:layout_below="@id/sql_im1"></EditText>
    <EditText
        android:id="@+id/sql_et2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:hint="密码"
        android:layout_marginTop="10dp"
        android:layout_below="@id/sql_et1"></EditText>

    <LinearLayout
        android:id="@+id/sql_lly1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_below="@id/sql_et2"
        android:layout_marginTop="20dp"
        android:padding="20dp">

        <Button
            android:id="@+id/sql_btn1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="添加"
            android:layout_marginRight="10dp"></Button>
        <Button
            android:id="@+id/sql_btn2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="查询"
            android:layout_marginRight="10dp"></Button>
        <Button
            android:id="@+id/sql_btn3"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="修改"
            android:layout_marginRight="10dp"></Button>
        <Button
            android:id="@+id/sql_btn4"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="删除"
            android:layout_marginRight="10dp"></Button>


    </LinearLayout>

    <TextView
        android:id="@+id/sql_tv1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/sql_lly1"
        android:layout_marginTop="20dp"
        android:text="用户："></TextView>


</RelativeLayout>

SQLiteDemoActivity

package com.example.test3;

import androidx.appcompat.app.AppCompatActivity;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.util.StringTokenizer;

public class SQLiteDemoActivity extends AppCompatActivity implements View.OnClickListener {

    private EditText ed1,ed2;
    private Button btn_add,btn_query,btn_modify,btn_delete;
    private TextView tv1;

    private MyHelper helper;

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


        helper = new MyHelper(this,"user.db",null,1);
        init();

    }

    public void init(){
        ed1 = findViewById(R.id.sql_et1);
        ed2 = findViewById(R.id.sql_et2);

        btn_add = findViewById(R.id.sql_btn1);
        btn_query = findViewById(R.id.sql_btn2);
        btn_modify = findViewById(R.id.sql_btn3);
        btn_delete = findViewById(R.id.sql_btn4);
        tv1 = findViewById(R.id.sql_tv1);

        btn_delete.setOnClickListener(this);
        btn_query.setOnClickListener(this);
        btn_modify.setOnClickListener(this);
        btn_add.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        SQLiteDatabase db;
        String username,password;
        String sql;

        switch (view.getId()){
            case R.id.sql_btn1:
                db = helper.getWritableDatabase();
                username = ed1.getText().toString();
                password = ed2.getText().toString();

                sql = "insert into user(username,password) values ('"+username+"','"+password+"')";
                db.execSQL(sql);
                Toast.makeText(this,"添加成功",Toast.LENGTH_SHORT).show();
                db.close();
                break;


            case R.id.sql_btn2:
                tv1.setText("");
                db = helper.getReadableDatabase();
                sql = "select username,password from user";
                Cursor cursor = db.rawQuery(sql,null);
                while (cursor.moveToNext()){

                    int index = cursor.getColumnIndex("username");
                    int index2 = cursor.getColumnIndex("password");
                    String username1 = cursor.getString(index);
                    String password1 = cursor.getString(index2);
                    tv1.append(username1+":"+password1+"\n");
                }
                cursor.moveToFirst();
                cursor.close();
                db.close();
                break;


            case R.id.sql_btn3:
                db = helper.getWritableDatabase();
                username = ed1.getText().toString();
                password = ed2.getText().toString();
                sql = "update user set password ='" + password + "' where username = '" + username + "'";
                db.execSQL(sql);
                Toast.makeText(this,"修改了",Toast.LENGTH_SHORT).show();
                db.close();
                break;


            case R.id.sql_btn4:
                db = helper.getWritableDatabase();
                username = ed1.getText().toString();
                sql ="delete from user where username = "+username;
                sql = "delete from user where username = '" + username + "'";
                db.execSQL(sql);
                Toast.makeText(this,"删除了",Toast.LENGTH_SHORT).show();
                db.close();
                break;

        }

    }
}