关于SQLite数据库的DAO操作

先上效果图：

核心代码：
activity_main.xml

xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:addStatesFromChildren="true" >
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="姓名"
            android:textColor="?android:attr/textColorSecondary" />
        <EditText
            android:id="@+id/et_name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:singleLine="true" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:addStatesFromChildren="true" >
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="年龄"
            android:textColor="?android:attr/textColorSecondary" />
        <EditText
            android:id="@+id/et_age"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:singleLine="true" />
    </LinearLayout>
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:addStatesFromChildren="true"
        android:gravity="center" >
        <Button
            android:id="@+id/bt_add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="添加" />
        <Button
            android:id="@+id/bt_modify"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="修改"/>
        <Button
            android:id="@+id/bt_del"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="删除" />
        <!--  <Button
             android:id="@+id/bt_query"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="查询"
             android:onClick="querybutton" >
         </Button> -->
    </LinearLayout>

    <ListView
        android:gravity="center"
        android:id="@+id/listView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:padding="5dip" >
    </ListView>

</LinearLayout>

list_item.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/tv_id"
        android:textSize="25sp"
        android:layout_width="50dp"
        android:layout_height="wrap_content"/>
    <TextView
        android:id="@+id/tvname"
        android:textSize="25sp"
        android:layout_width="100dp"
        android:layout_height="wrap_content"/>

    <TextView
        android:id="@+id/tvage"
        android:textSize="25sp"
        android:layout_width="50dp"
        android:layout_height="wrap_content"/>

</LinearLayout>

`
DbHelper.java`package com.example.mysqlite;

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

import androidx.annotation.Nullable;

public class DbHelper extends SQLiteOpenHelper {

    /*表名*/
    public static final String TB_NAME = "friends";

    public DbHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        /*当表不存在时，创建表*/
        db.execSQL("CREATE TABLE IF NOT EXISTS "
                + TB_NAME
                + " ( _id integer primary key autoincrement,"
                + " name varchar,"
                + " age integer" + ")");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        /*执行SQL命令*/
        db.execSQL("DROP TABLE IF EXISTS " + TB_NAME);
        onCreate(db);
    }
}

MyDAO.java

package com.example.mysqlite;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

/**
 * 调用数据库助手类DbHelper(用于打开数据库)
 * CRUD操作针对数据库test.db的表friends
 */
public class MyDAO {
    private SQLiteDatabase myDb;
    private DbHelper dbHelper;

    /*构造函数*/
    public MyDAO(Context context) {
        dbHelper = new DbHelper(context, "test.db", null, 1);
    }

    /**
     * 查询所有记录
     * @return
     */
    public Cursor allQuery() {
        myDb = dbHelper.getReadableDatabase();
        return myDb.rawQuery("select * from friends", null);
    }

    /**
     * 返回数据表记录数
     * @return
     */
    public int getRecordsNumber() {
        myDb = dbHelper.getReadableDatabase();
        Cursor cursor = myDb.rawQuery("select * from friends", null);
        return cursor.getCount();
    }

    /**
     * 插入数据
     * @param name
     * @param age
     */
    public void insertInfo(String name, int age) {
        myDb = dbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        long rowid = myDb.insert(DbHelper.TB_NAME, null, values);
        if (rowid == -1)
            Log.i("myDbDemo", "数据插入失败！");
        else
            Log.i("myDbDemo", "数据插入成功！" + rowid);
    }

    /**
     * 删除数据
     * @param selId
     */
    public void deleteInfo(String selId) {
        String where = "_id=" + selId;
        int i = myDb.delete(DbHelper.TB_NAME, where, null);
        if (i > 0)
            Log.i("myDbDemo", "数据删除成功！");
        else
            Log.i("myDbDemo", "数据未删除！");
    }

    /**
     * 修改数据
     * @param name
     * @param age
     * @param selId
     */
    public void updateInfo(String name, int age, String selId) {
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        String where = "_id=" + selId;
        int i = myDb.update(DbHelper.TB_NAME, values, where, null);

        /**
         * 更新数据库的原生方法为：
         * myDb.execSQL("update friends set name=?, age=? where _id=?", new Object[]{name, age, selId});
         */

        if (i > 0)
            Log.i("myDbDemo", "数据更新成功！");
        else
            Log.i("myDbDemo", "数据更新失败！");

    }
}

MainActivity.java

package com.example.mysqlite;

import androidx.appcompat.app.AppCompatActivity;

import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private MyDAO myDAO;    // 数据库访问对象
    private ListView listView;
    private List<Map<String, Object>> listData;
    private Map<String, Object> listItem;
    private SimpleAdapter listAdapter;

    // id(自增长字段), name, age
    private EditText et_name;
    private EditText et_age;

    private String selId = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button bt_add= findViewById(R.id.bt_add);
        bt_add.setOnClickListener(this);
        Button bt_modify= findViewById(R.id.bt_modify);
        bt_modify.setOnClickListener(this);
        Button bt_del= findViewById(R.id.bt_del);
        bt_del.setOnClickListener(this);

        et_name = findViewById(R.id.et_name);
        et_age = findViewById(R.id.et_age);

        myDAO = new MyDAO(this);
        /*初始化数据*/
        if (myDAO.getRecordsNumber() == 0) {
            myDAO.insertInfo("zjh", 21);
        }
        displayRecords();

    }

    /**
     * 显示数据
     */
    public void displayRecords() {
        listView = findViewById(R.id.listView);
        listData = new ArrayList<Map<String, Object>>();
        Cursor cursor = myDAO.allQuery();
        /*循环遍历所有数据*/
        while (cursor.moveToNext()) {
            /**
             * 获取数据的两种方式：
             * 1.cursor.getInt(columnIndex) 通过列号获取数据
             * 2.cursor.getInt(columnName)  通过列名称获取数据
             */
            int id = cursor.getInt(0);
            String name = cursor.getString(1);
            int age = cursor.getInt(cursor.getColumnIndex("age"));
            listItem = new HashMap<>(); // 必须在循环内部创建
            listItem.put("_id", id);
            listItem.put("name", name);
            listItem.put("age", age);
            listData.add(listItem);
        }
        listAdapter = new SimpleAdapter(this,
                listData,
                R.layout.list_item,
                new String[]{"_id", "name", "age"},
                new int[]{R.id.tv_id, R.id.tvname, R.id.tvage});
        listView.setAdapter(listAdapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView> parent, View view, int position, long id) {
                Map<String, Object> rec = (Map<String, Object>) listAdapter.getItem(position);
                et_name.setText(rec.get("name").toString());
                et_age.setText(rec.get("age").toString());
                Log.i("ly", rec.get("_id").toString());
                selId = rec.get("_id").toString();
            }
        });
    }

    @Override
    public void onClick(View v) {

        if (selId != null) {
            String p1 = et_name.getText().toString().trim();
            int p2 = Integer.parseInt(et_age.getText().toString());
            switch (v.getId()) {
                case R.id.bt_add:
                    myDAO.insertInfo(p1, p2);
                    break;
                case R.id.bt_modify:
                    myDAO.updateInfo(p1, p2, selId);
                    break;
                case R.id.bt_del:
                    myDAO.deleteInfo(selId);
                    Toast.makeText(getApplicationContext(), "删除成功~", Toast.LENGTH_SHORT).show();
                    et_name.setText(null);
                    et_age.setText(null);
                    selId = null;
            }
        } else {// 未选择列表项
            // 点击添加按钮
            if (v.getId() == R.id.bt_add) {
                String p1 = et_name.getText().toString();
                String p2 = et_age.getText().toString();
                if (p1.equals("") || p2.equals("")) {
                    Toast.makeText(getApplicationContext(), "姓名和年龄不能为空！", Toast.LENGTH_SHORT).show();
                } else {
                    myDAO.insertInfo(p1, Integer.parseInt(p2));
                }
            } else {
                // 点击修改或删除按钮
                Toast.makeText(getApplicationContext(), "请选择记录！", Toast.LENGTH_SHORT).show();
            }
        }
        displayRecords();

    }
}

另外，如何在WECHAT项目中使用“通讯录”模块？
核心代码如下

package com.example.myweixin;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.content.DialogInterface;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.Window;
import android.widget.FrameLayout;
import android.widget.ImageButton;
import android.widget.LinearLayout;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 private Fragment mtab01=new weixinFragment();
    private Fragment mtab02=new friendFragment();
    private Fragment mtab03=new contactFragment();
    private Fragment mtab04=new setFragment();
    private FragmentManager fm;

    private  LinearLayout mtabweixin;
    private  LinearLayout mtabfrd;
    private  LinearLayout mtabaddress;
    private  LinearLayout mtabset;
    private  ImageButton mimgweixin;
    private  ImageButton mimgfrd;
    private  ImageButton mimgaddress;
    private  ImageButton mimgset;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        initFragment();
   initEvent();

        selectfragment(0);

    }
    private  void initFragment(){
        fm=getSupportFragmentManager();
        FragmentTransaction transaction=fm.beginTransaction();
        transaction.add(R.id.id_content,mtab01);
        transaction.add(R.id.id_content,mtab02);
        transaction.add(R.id.id_content,mtab03);
        transaction.add(R.id.id_content,mtab04);
        transaction.commit();
    }

    private  void initView(){

        mtabweixin=(LinearLayout) findViewById(R.id.weixin);
        mtabfrd=(LinearLayout) findViewById(R.id.frd);
        mtabaddress=(LinearLayout) findViewById(R.id.contact);
        mtabset=(LinearLayout) findViewById(R.id.setting);

        mimgweixin=findViewById(R.id.imageButton1);
        mimgfrd=findViewById(R.id.imageButton2);
        mimgaddress=findViewById(R.id.imageButton3);
        mimgset=findViewById(R.id.imageButton4);
    }
  private  void initEvent(){
        mtabweixin.setOnClickListener(this);
      mtabfrd.setOnClickListener(this);
      mtabaddress.setOnClickListener(this);
      mtabset.setOnClickListener(this);
  }
    private void hidefragment(FragmentTransaction transaction){

        transaction.hide(mtab01);
        transaction.hide(mtab02);
        transaction.hide(mtab03);
        transaction.hide(mtab04);
    }
    private  void  selectfragment(int i){
        FragmentTransaction transaction=fm.beginTransaction();
        hidefragment(transaction);
        switch (i){
            case 0:
                transaction.show(mtab01);
                mimgweixin.setImageResource(R.drawable.tab_weixin_pressed);
                break;
            case 1:
                transaction.show(mtab02);
                mimgfrd.setImageResource(R.drawable.tab_find_frd_pressed);
                break;
            case 2:
                transaction.show(mtab03);
                mimgaddress.setImageResource(R.drawable.tab_address_pressed);
                break;
            case 3:
                transaction.show(mtab04);
                mimgset.setImageResource(R.drawable.tab_settings_pressed);
                break;
            default:
                break;
        }
        transaction.commit();
    }

    @Override
    public void onClick(View v){
        resetimg();

        switch (v.getId()){
            case R.id.imageButton1:
                selectfragment(0);
              System.out.println(v.getId());
                break;
            case R.id.imageButton2:
                selectfragment(1);
                break;
            case R.id.imageButton3:
                selectfragment(2);
                break;
            case R.id.imageButton4:
                selectfragment(3);
                break;
            default:
                break;
        }

    }
    public  void  resetimg(){
        mimgweixin.setImageResource(R.drawable.tab_weixin_normal);
        mimgfrd.setImageResource(R.drawable.tab_find_frd_normal);
        mimgaddress.setImageResource(R.drawable.tab_address_normal);
        mimgset.setImageResource(R.drawable.tab_settings_normal);
    }

}

参考网址：http://www.wustwzx.com/as/sy/sy07.html#mk2
完整代码：https://gitee.com/zhangjianhui1010/SQLite_DAO