通讯录

<?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=".MainActivity">

    <TextView
        android:id="@+id/tv_1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="姓名"
        android:textSize="20sp"
        android:layout_marginTop="30dp"
        android:layout_marginLeft="20dp"
        android:padding="10dp"/>

    <EditText
        android:id="@+id/et_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入姓名"
        android:layout_toRightOf="@id/tv_1"
        android:layout_marginTop="30dp"
        android:textSize="20sp"/>

    <TextView
        android:id="@+id/tv_2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="电话"
        android:textSize="20sp"
        android:layout_marginLeft="20dp"
        android:layout_below="@id/tv_1"
        android:padding="10dp"/>

    <EditText
        android:id="@+id/et_phone"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入手机号码"
        android:layout_toRightOf="@id/tv_2"
        android:layout_below="@id/et_name"
        android:textSize="20sp"/>

    <Button
        android:id="@+id/btn_add"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="添加"
        android:textSize="18sp"
        android:layout_below="@id/tv_2"
        android:layout_marginTop="20dp"
        android:layout_marginLeft="20dp"/>
    <Button
        android:id="@+id/btn_query"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="查询"
        android:textSize="18sp"
        android:layout_below="@id/et_phone"
        android:layout_toRightOf="@id/btn_add"
        android:layout_marginTop="20dp" />
    <Button
        android:id="@+id/btn_update"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="修改"
        android:textSize="18sp"
        android:layout_below="@id/et_phone"
        android:layout_toRightOf="@id/btn_query"
        android:layout_marginTop="20dp" />
    <Button
        android:id="@+id/btn_delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="删除"
        android:textSize="18sp"
        android:layout_below="@id/et_phone"
        android:layout_toRightOf="@id/btn_update"
        android:layout_marginTop="20dp" />
    <TextView
        android:id="@+id/tv_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn_add"
        android:textSize="18sp"
        android:layout_marginLeft="20dp"/>




</RelativeLayout>

package com.example.directory;

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

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

public class MyHelper extends SQLiteOpenHelper {

    public MyHelper(Context context) {
        super(context, "stu.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))");
    }

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

    }
}

package com.example.directory;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentValues;
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 static com.example.directory.R.*;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private  MyHelper myHelper;
    private EditText mEtName;
    private EditText mEtPhone;
    private TextView mTvShow;
    private Button mBtnAdd;
    private Button mBtnQuery;
    private Button mBtnUpdate;
    private Button mBtnDelete;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(layout.activity_main);
        myHelper = new MyHelper(this);
        init();

    }

    private void init() {
        mEtName = (EditText) findViewById(id.et_name);
        mEtPhone = (EditText) findViewById(id.et_phone);
        mTvShow = (TextView) findViewById(id.tv_show);
        mBtnAdd = (Button) findViewById(id.btn_add);
        mBtnQuery = (Button) findViewById(id.btn_query);
        mBtnUpdate = (Button) findViewById(id.btn_update);
        mBtnDelete = (Button) findViewById(id.btn_delete);
        mBtnAdd.setOnClickListener(this);
        mBtnQuery.setOnClickListener(this);
        mBtnUpdate.setOnClickListener(this);
        mBtnDelete.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        String name;
        String phone;
        SQLiteDatabase db;
        ContentValues values;
        switch (v.getId()) {

            case R.id.btn_add:
                name = mEtName.getText().toString();
                phone = mEtPhone.getText().toString();
                db = myHelper.getWritableDatabase();
                values = new ContentValues();
                values.put("name", name);
                values.put("phone", phone);
                db.insert("information", null, values);
                Toast.makeText(this, "信息已添加", Toast.LENGTH_SHORT).show();
                db.close();
                break;

            case id.btn_query:
                db = myHelper.getReadableDatabase();
                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) + "  ；Tel :  " + cursor.getString(2));
                }
                while (cursor.moveToNext()) {
                    mTvShow.append("\n" + "Name :  " + cursor.getString(1) +
                            "  ；Tel :  " + cursor.getString(2));
                }
                cursor.close();
                db.close();
                break;

            case id.btn_update:
                db = myHelper.getWritableDatabase();
                values = new ContentValues();
                values.put("phone", phone = mEtPhone.getText().toString());
                db.update("information", values, "name=?",
                        new String[]{mEtName.getText().toString()}); // 更新并得到行数
                Toast.makeText(this, "信息已修改", Toast.LENGTH_SHORT).show();
                db.close();
                break;

            case id.btn_delete:
                db = myHelper.getWritableDatabase();
                db.delete("information", null, null);
                Toast.makeText(this, "信息已删除", Toast.LENGTH_SHORT).show();
                mTvShow.setText("");
                db.close();
                break;

        }
    }
}