Android Studio连接SQLlite

1.

MainActivity.java

package com.example.dbproject;

import android.database.sqlite.SQLiteDatabase;
import android.view.View;
import android.widget.Button;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
    DbContect helper;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        helper=new DbContect(  MainActivity.this);
        Button btn=findViewById(R.id.create);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View V) {
                SQLiteDatabase db=helper.getWritableDatabase();
            }
        });
    }
}

2.DbContect.java

package com.example.dbproject;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Toast;
public class DbContect extends SQLiteOpenHelper {
    private static final int VERSION=1;
    private static final String DBNAME="Users.db";   //  创建数据库名叫 Users
    private Context mContext;

    public DbContect(Context context){
        super(context,DBNAME,null,VERSION);
        mContext = context;
    }
    //创建数据库
    public void onCreate(SQLiteDatabase db){
        //创建密码表  pwd_tb
        db.execSQL("create table pwd_tb (pwd varchar(20) primary key)");
        //创建收入表    user_tb
        db.execSQL("create table user_tb(_id integer primary key autoincrement, money decimal," +
                " time varchar(10),type varchar(10),handler varchar(100),mark varchar(200))");
    }
    //数据库版本更新
    public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion)
    {
        db.execSQL("drop table if exists pwd_tb");
        db.execSQL("drop table if exists user_tb");
        onCreate(db);
    }


}

3.activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <LinearLayout android:layout_width="match_parent"
        android:layout_height="match_parent">
        <Button
            android:id="@+id/create"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="#00BCD4"
            android:textSize="22dp"
            android:text="点击创建Users数据库"
            >
        </Button>
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>