掌握常用布局和基本控件的使用方法
掌握界面图像显示的使用方法
掌握SQLite数据库的创建和基本操作方法
通过线性布局和相对布局来搭建Activity界面，在MainActivity中编写逻辑代码，运行程序，输入两条联系人信息分别点击“添加”“查询”“修改”“删除”按钮。实现联系人信息的添加、查询、修改以及删除功能。操作成功后，通过弹出的消息内容显示对应操作。下图界面仅供参考，可根据功能另外设计界面。
activity_main.xml
我在原有界面上加了一个条件输入框，以便条件查询、修改和删除时通过用户姓名来执行操作。
MainActivity.java
package com.example.shiyan5;import androidx.annotation.Nullable;import androidx.appcompat.app.AppCompatActivity;import android.content.ContentValues;import android.content.Context;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;public class MainActivity extends AppCompatActivity implements View.OnClickListener {private Button add, select, update, delete, conditionalQueryBtn;private EditText name, telNumber, conditionalQueryEt;private TextView showInfo;private SQLiteDatabase db;private MyDbHelper myDbHelper;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initVeiw();add.setOnClickListener(this);select.setOnClickListener(this);update.setOnClickListener(this);delete.setOnClickListener(this);conditionalQueryBtn.setOnClickListener(this);conditionalQueryEt.setOnClickListener(this);myDbHelper = new MyDbHelper(this, "MyDatabase.db", null, 669);}private void initVeiw() {add = findViewById(R.id.addBtn);select = findViewById(R.id.selectBtn);update = findViewById(R.id.updateBtn);delete = findViewById(R.id.deleteBtn);name = findViewById(R.id.et1);telNumber = findViewById(R.id.et2);showInfo = findViewById(R.id.showInfo);conditionalQueryEt = findViewById(R.id.et3);conditionalQueryBtn = findViewById(R.id.conditional_query_btn);}@Overridepublic void onClick(View view) {switch (view.getId()) {case R.id.addBtn:db = myDbHelper.getWritableDatabase();String userName = name.getText().toString();String telephoneNumber = telNumber.getText().toString();//SQLiteDatabase的insert方法来添加/* ContentValues contentValues = new ContentValues();contentValues.put("userName", userName);contentValues.put("telephoneNumber", telephoneNumber);db.insert("user", null, contentValues);*///返回的是插入记录的索引号,也就是第多少条。db.execSQL("insert into user(username,telephoneNumber) values(" />0) {Toast.makeText(this, "查询成功！！", Toast.LENGTH_SHORT).show();while (cursor.moveToNext()) {showInfo.append("姓名：" + cursor.getString(0) + "电话号码：" + cursor.getString(1) + "\n");}} else {Toast.makeText(this, "一条数据都没有呢~~", Toast.LENGTH_SHORT).show();}cursor.close();db.close();break;case R.id.conditional_query_btn:db=myDbHelper.getReadableDatabase();String conditionalQuery=conditionalQueryEt.getText().toString();Cursor cursor1=db.query("user",new String[]{"userName", "telephoneNumber"},"userName=?",new String[]{conditionalQuery},null,null,null,null);//Cursor cursor1 =db.rawQuery("select userName,telephoneNumber from user where userName=?",new String[]{conditionalQuery});showInfo.setText("查询结果：\n");if (cursor1.getCount()>0) {Toast.makeText(this, "查询成功！！", Toast.LENGTH_SHORT).show();while (cursor1.moveToNext()){showInfo.append("姓名：" + cursor1.getString(0) + "电话号码：" + cursor1.getString(1) + "\n");}}else{Toast.makeText(this, "没找到呢~~", Toast.LENGTH_SHORT).show();}cursor1.close();db.close();break;case R.id.updateBtn:db=myDbHelper.getWritableDatabase();ContentValues contentValues1=new ContentValues();String userName1 = name.getText().toString();String telephoneNumber1= telNumber.getText().toString();String conditionalQuery2=conditionalQueryEt.getText().toString();contentValues1.put("userName", userName1);contentValues1.put("telephoneNumber", telephoneNumber1);int a=db.update("user",contentValues1,"userName=?",new String[]{conditionalQuery2});if (a>0) {Toast.makeText(this, "更改成功，共更改了"+a+"条数据", Toast.LENGTH_SHORT).show();}else{Toast.makeText(this, "更改失败", Toast.LENGTH_SHORT).show();}//db.execSQL("update user set userName=?,telephoneNumber=? where userName=?",new Object[]{userName1,telephoneNumber1,conditionalQuery2});db.close();break;case R.id.deleteBtn:db=myDbHelper.getWritableDatabase();String conditionalQuery1=conditionalQueryEt.getText().toString();//db.execSQL("delete from user where userName=?",new Object[]{conditionalQuery1});int i=db.delete("user","userName=?",new String[]{conditionalQuery1});//返回删除的条数。if(i>0){Toast.makeText(this, "删除成功，共删除了"+i+"条数据", Toast.LENGTH_SHORT).show();}else{Toast.makeText(this, "删除失败", Toast.LENGTH_SHORT).show();}db.close();break;}}class MyDbHelper extends SQLiteOpenHelper {public MyDbHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {super(context, name, factory, version);}@Overridepublic void onCreate(SQLiteDatabase sqLiteDatabase) {sqLiteDatabase.execSQL("create table user(user_id integer primary key autoincrement,userName varchar(10),telephoneNumber varchar(20))");}@Overridepublic void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {}}}增删改查我写了两种方式，第一种是db.execSQL()直接用SQL语句进行操作，第二种使用 SQLiteDatabase中自带的增删改查的方法：db.insert() db.query() db.update() db.delete()。
哈哈
哈哈哈
我对着潮汐推敲什么是以静制动
山林间迷雾
能不能当障眼法的内容
月转星移的轨迹跟临军布阵相同
风林火山是不是用兵之重
到最后必然是我运筹帷幄
你最后放弃抵抗
我仰望着夕阳
你低头黯然离场
听我说胜败是兵家之常
你不用放在心上
是因为我只适合