Android实现通讯录功能

package com.example.sqlite;

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) {
    super(context, "test.db", null, 1);
  }

  //当数据库第一次创建的时候执行
  @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.sqlite;
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.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private TextView name;
private TextView phone;
private Button btnAdd;
private Button btnDel;
private Button btnUqd;
private Button btnSel;
private String uPhone;
private String uName;
private MyHelper myHelper;
private SQLiteDatabase db;
private TextView show;
private ContentValues contentValues;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myHelper = new MyHelper(this);
init();
}
private void init() {
show = findViewById(R.id.show);
name = findViewById(R.id.name);
phone = findViewById(R.id.phone);
btnAdd = findViewById(R.id.insert);
btnDel = findViewById(R.id.delete);
btnUqd = findViewById(R.id.update);
btnSel = findViewById(R.id.select);
btnAdd.setOnClickListener(this);
btnDel.setOnClickListener(this);
btnUqd.setOnClickListener(this);
btnSel.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.select:
db = myHelper.getReadableDatabase();
Cursor cursor = db.query("information", null, null, null, null, null, null);
if (cursor.getCount() == 0) {
Toast.makeText(this, "没有数据", Toast.LENGTH_LONG).show();
} else {
cursor.moveToFirst();
show.setText("Name:" + cursor.getString(1) + "Tel:" + cursor.getString(2));
}
while (cursor.moveToNext()) {
show.append("n" + "Name" + cursor.getString(1) + "Tel" + cursor.getString(2));
}
cursor.close();
db.close();
break;
case R.id.insert:
uName = name.getText().toString();
uPhone = phone.getText().toString();
db = myHelper.getReadableDatabase();
contentValues = new ContentValues();
contentValues.put("name", uName);
contentValues.put("phone", uPhone);
db.insert("information", null, contentValues);
db.close();
break;
case R.id.update:
db = myHelper.getReadableDatabase();
contentValues = new ContentValues();
contentValues.put("phone", uPhone = phone.getText().toString());
db.update("information", contentValues, "name=?", new String[]{name.getText().toString()});
db.close();
break;
case R.id.delete:
db = myHelper.getReadableDatabase();
db.delete("information", null, null);
Toast.makeText(this, "信息已经删除", Toast.LENGTH_LONG).show();
show.setText("");
db.close();
break;
}
}
}

<?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"
android:background="@drawable/background" 
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
<ImageView
android:layout_width="160dp"
android:layout_height="120dp"
android:layout_marginTop="50dp"
android:layout_marginLeft="20dp"
android:src="@drawable/expression" </ImageView 
<ImageView
android:layout_width="160dp"
android:layout_height="120dp"
android:layout_marginTop="50dp"
android:layout_marginLeft="20dp"
android:src="@drawable/text" </ImageView 
</LinearLayout 
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_marginTop="20dp"
android:paddingHorizontal="20dp"
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="姓 名 :"
android:textSize="26sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" / 
<EditText
android:id="@+id/name"
android:layout_width="0dp"
android:layout_weight="3"
android:layout_height="wrap_content"
android:hint="请输入姓名"
android:textSize="22sp"
</EditText 
</LinearLayout 
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_marginTop="20dp"
android:paddingHorizontal="20dp"
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="电 话 :"
android:textSize="26sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" / 
<EditText
android:id="@+id/phone"
android:layout_width="0dp"
android:layout_weight="3"
android:layout_height="wrap_content"
android:hint="请输入手机号码"
android:textSize="22sp"
</EditText 
</LinearLayout 
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:layout_marginTop="20dp"
android:paddingHorizontal="20dp"
<Button
android:id="@+id/insert"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="增加"
android:textSize="26sp"
</Button 
<Button
android:id="@+id/select"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="查询"
android:textSize="26sp"
</Button 
<Button
android:id="@+id/update"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="修改"
android:textSize="26sp"
</Button 
<Button
android:id="@+id/delete"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="删除"
android:textSize="26sp"
</Button 
</LinearLayout 
<TextView
android:id="@+id/show"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:textSize="18sp"
android:background="#80ffffff"
android:layout_marginHorizontal="20dp"
</TextView 
</LinearLayout 
</RelativeLayout