通讯录增删改查

package com.example.ks;


import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
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 androidx.appcompat.app.AppCompatActivity;
import java.io.Serializable;

public class MainA extends AppCompatActivity implements View.OnClickListener {
    MyHelper myHelper;
    private EditText mEtName;
    private EditText mEtPhone;
    private EditText mEtEmail;
    private TextView mTvShow;
    private Button mBtAdd;
    private Button mBtQuery;
    private Button mBtUpdate;
    private Button mBtDelete;
    public String name;
    public String phone;
    public String email;
    public SQLiteDatabase db;
    public ContentValues values;
    private int totalCount=0;
    Button Btn1,Btn2,Btn3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_m);
        myHelper = new MyHelper(this);
        init();
//登录
        Btn1=findViewById(R.id.btn_2);
        Btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(MainA.this,MainActivity2.class);
                startActivity(intent);
            }
        });
        //音乐库
        Btn2=findViewById(R.id.btn_3);
        Btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(MainA.this,MainActivity4.class);
                startActivity(intent);
            }
        });


        //排行榜
        Btn3=findViewById(R.id.btn_8);
        Btn3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(MainA.this,LA.class);
                startActivity(intent);
            }
        });


    }
    //实例化界面，获取各个控件的值
    private void init() {
        mEtName = (EditText) findViewById(R.id.et_name);
        mEtPhone = (EditText) findViewById(R.id.et_phone);
        mEtEmail = (EditText) findViewById(R.id.et_email);
        mTvShow = (TextView) findViewById(R.id.ld_show);
        mBtAdd = (Button) findViewById(R.id.btn_add);
        mBtUpdate = (Button) findViewById(R.id.btn_update);
        mBtQuery = (Button) findViewById(R.id.btn_query);
        mBtDelete = (Button) findViewById(R.id.btn_delete);
        mBtAdd.setOnClickListener(this);
        mBtUpdate.setOnClickListener(this);
        mBtQuery.setOnClickListener(this);
        mBtDelete.setOnClickListener(this);
    }

    @Override
    //点击事件
    public void onClick(View v) {
        switch(v.getId()) {
            //添加数据
            case R.id.btn_add:
                addText();
                queryText();
                break;
            //查询数据
            case R.id.btn_query:
                queryText();
                break;
            //修改数据
            case R.id.btn_update:
                updateText();
                queryText();
                break;
            //删除数据
            case R.id.btn_delete:
                deleteText();
                queryText();
                break;

        }
    }
    //添加数据
    public void addText() {
        name = mEtName.getText().toString();
        phone = mEtPhone.getText().toString();
        email = mEtEmail.getText().toString();
        //获取可读写的SQLiteDatabase对象
        db = myHelper.getWritableDatabase();
        //创建ContentValues对象
        values = new ContentValues();
        //将数据添加到ContentValues对象
        values.put("name",name);
        values.put("phone",phone);
        values.put("email",email);
        db.insert("information",null,values);
        Toast.makeText(this,"添加数据成功",Toast.LENGTH_SHORT).show();
        db.close();
    }
    //查询数据
    public void queryText() {
        db = myHelper.getWritableDatabase();
        Cursor cursor = db.query("information",null,null,null,null,null,null);
        if(cursor.getCount() == 0) {
            mTvShow.setText("");
            Toast.makeText(this,"没有数据",Toast.LENGTH_SHORT).show();
        }
        else{
            cursor.moveToFirst();
            mTvShow.setText("Name:" + cursor.getString(1) + "\t" + "tel:" + cursor.getString(2) + "\t" + "email:" + cursor.getString(3));
        }
        while(cursor.moveToNext()) {
            mTvShow.append("\n" + "Name:" + cursor.getString(1) + "\t" + "|tel:" + cursor.getString(2) + "\t" + "|email:" + cursor.getString(3));
        }
        cursor.close();
        db.close();
    }
    //修改数据
    public void updateText() {
        db = myHelper.getWritableDatabase();
        //实例化一个要修改的数据的对象
        values = new ContentValues();
        values.put("phone",phone = mEtPhone.getText().toString());
        values.put("email",email = mEtEmail.getText().toString());
        //更新并得到行数
        db.update("information",values,"name = ?",new String[]{mEtName.getText().toString()});
        Toast.makeText(this, "数据修改成功", Toast.LENGTH_SHORT).show();
        db.close();
    }
    //删除数据
    public void deleteText() {
        db = myHelper.getWritableDatabase();
        int i = db.delete("information","name=?",new String[]{mEtName.getText().toString()});
        if(i !=0 ) {
            Toast.makeText(this,"删除数据成功",Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(this,"删除数据失败",Toast.LENGTH_SHORT).show();
        }
        db.close();
    }
    class MyHelper extends SQLiteOpenHelper {
        public MyHelper(Context context) {
            super(context,"lvdou.db",null,1);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL("Create table information(_id integer primary key autoincrement, name varchar(20), phone varchar(20), email varchar(20))");
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

        }
    }
}

<?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"
android:paddingTop="20dp"
android:paddingRight="20dp"
android:paddingBottom="20dp"
android:paddingLeft="20dp"
android:background="@drawable/music1"
tools:context=".MainA">


<ImageView
    android:id="@+id/imageView"
    android:layout_width="125dp"
    android:layout_height="110dp"
    android:layout_centerHorizontal="true"
    app:srcCompat="@drawable/in" />

<LinearLayout
    android:id="@+id/ld_name"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_above="@+id/ld_phone"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="25sp"
        android:text="姓名：" />

    <EditText
        android:id="@+id/et_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:ems="10"
        android:inputType="textPersonName"
        android:textSize="20sp"
        android:hint="请输入姓名" />

</LinearLayout>

<LinearLayout
    android:id="@+id/ld_phone"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_above="@+id/ld_email"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="25sp"
        android:text="电话：" />

    <EditText
        android:id="@+id/et_phone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:ems="10"
        android:inputType="textPersonName"
        android:textSize="20sp"
        android:hint="请输入电话" />
</LinearLayout>

<LinearLayout
    android:id="@+id/ld_email"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="10dp"
    android:layout_above="@+id/ld_btn"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="25sp"
        android:text="邮箱：" />

    <EditText
        android:id="@+id/et_email"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:ems="10"
        android:inputType="textPersonName"
        android:textSize="20sp"
        android:hint="请输入邮箱"/>
</LinearLayout>

<LinearLayout
    android:id="@+id/ld_btn"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_centerVertical="true"
    android:orientation="horizontal">

    <Button
        android:id="@+id/btn_add"
        android:background="@drawable/shape"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="20sp"
        android:layout_alignTop="@+id/button"
        android:layout_toEndOf="@+id/button"
        android:text="添加"
        android:layout_toRightOf="@+id/button" />

    <Button
        android:id="@+id/btn_update"
        android:background="@drawable/shape"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="20sp"
        android:text="修改" />

    <Button
        android:id="@+id/btn_query"
        android:background="@drawable/shape"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:layout_weight="1"
        android:text="查询" />

    <Button
        android:id="@+id/btn_delete"
        android:background="@drawable/shape"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="20sp"
        android:text="删除" />

</LinearLayout>

<TextView
    android:id="@+id/ld_show"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="25dp"
    android:layout_below="@+id/ld_btn"
    android:textSize="20sp" />

<Button
    android:id="@+id/btn_2"
    android:layout_width="174dp"
    android:layout_height="wrap_content"
    android:layout_below="@+id/editText4"
    android:layout_marginTop="470dp"
    android:background="@drawable/btn_bg_selector"
    android:text="返回列表"
    android:textSize="20sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.529"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.382"
    tools:ignore="UnknownId" />
    <Button
        android:id="@+id/btn_3"
        android:layout_width="174dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText4"
        android:layout_marginTop="520dp"
        android:background="@drawable/btn_bg_selector"
        android:text="查看/创建音乐库"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.529"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.382"
        tools:ignore="UnknownId" />
    <Button
        android:id="@+id/btn_8"
        android:layout_width="174dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText4"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="570dp"
        android:background="@drawable/btn_bg_selector"
        android:text="查看排行榜"
        android:textSize="20sp"
        tools:ignore="UnknownId" />

</RelativeLayout>