商品展示，以及增 删 改 查功能

首先我们先创建一个名为“商品展示”的应用程序，再现对应的布局文件（activity_main.xml）编写基本的界面代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginTop="8dp"
    tools:context="com.example.bz0209.a12lab07.MainActivity"
    android:orientation="vertical">



    <LinearLayout
        android:id="@+id/addLL"
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:id="@+id/nameET"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="商品名称"
            android:inputType="textPersonName"
            />
        <EditText
            android:id="@+id/balanceET"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="金额"
            android:inputType="number"
            />
        <ImageView
            android:id="@+id/addIV"
            android:onClick="add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@android:drawable/ic_input_add"/>
    </LinearLayout>
    <ListView
        android:id="@+id/accountLV"
        android:layout_width="match_parent"
        android:layout_height="424dp"
        android:layout_below="@id/addLL"></ListView>
</LinearLayout>

其次创建ListView 布局 ：用于展示商品的基本案列，该布局创建了三个Textview 和三个ImageView

三个TextView：id ，商品名称，金额。三个ImageView：增加金额，减少金额，删除金额。

具体代码如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:padding="10dp">
    <TextView
        android:id="@+id/idTV"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="13"
        android:textColor="#000000"
        android:textSize="20sp"/>
    <TextView
        android:id="@+id/nameTV"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:singleLine="true"
        android:text="PQ"
        android:textColor="#000000"
        android:textSize="20sp"/>
    <TextView
        android:id="@+id/balanceTV"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:singleLine="true"
        android:text="12345"
        android:textColor="#000000"
        android:textSize="20sp"/>
        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical">
            <ImageView

                android:id="@+id/upIV"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="2dp"
                android:src="@android:drawable/arrow_up_float"
                />
            <ImageView
                android:id="@+id/downIV"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:src="@android:drawable/arrow_down_float"
                />
        </LinearLayout>
    <ImageView
        android:id="@+id/deleteIV"
        android:layout_width="25dp"
        android:layout_height="25dp"
        android:src="@android:drawable/ic_menu_delete"
        />
</LinearLayout>

三·创建数据库在第一个文件（com.example.bz0209.a12lab07）下创建一个名为dao的包 用于定义一个MyHelper类继承SQLIteOpenHelper 代码如下：

package com.example.bz0209.a12lab07.dao;

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

/**
 * Created by Administrator on 2017/4/17.
 */

public class MyHelper extends SQLiteOpenHelper {
    public MyHelper(Context context){
        super(context,"itcast.db",null,2);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        System.out.println("onCreate");
        db.execSQL("create table account(_id integer primary key autoincrement," +
                "name varchar(20)" +
                "balance integer");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {
        System.out.println("onUpgrade");
    }
}

四· 再操作数据库库时将数据存放至一个javabean对象中操作起来更加方便。所以 需要在第一个文件下继续创建一个bean包来存放javaBean类，在bean包下继续创建一个Account类 代码如下：

package com.example.bz0209.a12lab07.bean;

/**
 * Created by Administrator on 2017/4/17.
 */

public class Account {
    private Long id;
    private String name;
    private  Integer balance;
    public Long getId(){
        return id;
    }
    public void setId(Long id){
        this.id=id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getBalance() {
        return balance;
    }

    public void setBalance(Integer balance) {
        this.balance = balance;
    }
    public Account(String id, String name, Integer balance){
        super();
        this.id=id;
        this.name=name;
        this.balance=balance;
    }
    public Account(String name,Integer balance){
        super();
        this.name=name;
        this.balance=balance;
    }
    public Account(){
        super();
    }
    public String toString(){
        return "[序号:"+id+",商品名称："+name+",余额："+balance+"]";
    }
}

五·创建数据逻辑操作类：

package com.example.bz0209.a12lab07.dao;

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

import com.example.bz0209.a12lab07.bean.Account;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Administrator on 2017/4/17.
 */

public class AccountDao {
    private MyHelper helper;
    public AccountDao(Context context){
        helper=new MyHelper(context);
    }
    public void insert(Account account){
        SQLiteDatabase db=helper.getWritableDatabase();
        ContentValues values=new ContentValues();
        values.put("name",account.getName());
        values.put("balance",account.getBalance());
        long id=db.insert("account",null,values);
        account.setId(id);
        db.close();
    }
    public  int delete(long id){
        SQLiteDatabase db=helper.getWritableDatabase();
        int count=db.delete("account","_id=?",new String[]{id+""});
        db.close();
        return count;
    }
    public int updata(Account account){
        SQLiteDatabase db=helper.getWritableDatabase();
        ContentValues values=new ContentValues();
        values.put("name",account.getName());
        values.put("balance",account.getBalance());
        int count=db.update("account",values,"_id=?", new String[]{account.getId()+""});
        db.close();
        return count;
    }
    public List<Account> queryAll(){
        SQLiteDatabase db=helper.getReadableDatabase();
        Cursor c=db.query("account",null,null,null,null,null,"balance DESC");
        List<Account> list=new ArrayList<Account>();
        while (c.moveToNext()){
            long id=c.getLong(c.getColumnIndex("_id"));
            String name=c.getString(1);
            int balance=c.getInt(2);
            list.add(new Account(id,name,balance));
        }
        c.close();
        db.close();
        return list;
    }
}

上述代码是逻辑操作类AccountDao，该类创建了对数据进行增、删、改、查操作的方法。需要注意的是，在7~18行代码中的insert（）方法中调用了db.insert（）方法，这个方法第二个参数如果传入null，是无法插入一条空数据的。如果相差如一条空数据，第二个参数必须写一个列名（任意列），传入这个列名是用来拼接SQL语句的。

六·最后编写界面交互代码（MainActivity）

数据库操作完成之后需要界面与数据库进行交互，用户实现将数据库中的数据以ListView的形式展示在界面上。

具体代码如下：

package com.example.bz0209.a12lab07;

import android.app.Activity;
import android.media.Image;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.DialogTitle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import com.example.bz0209.a12lab07.bean.Account;
import com.example.bz0209.a12lab07.dao.AccountDao;

import java.util.List;
import java.util.Objects;

public class MainActivity extends Activity {
       //配备适合的数据集合
    private List<Account>list;
    private AccountDao dao;
    private EditText nameET;
    private ListView accountLV;
    private EditText balanceET;
    private MyAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        dao=new AccountDao(this);
        list=dao.queryAll();
        adapter=new MyAdapter();
        accountLV.setAdapter(adapter);
    }
    private void initView(){
        accountLV=(ListView) findViewById(R.id.accountLV);
        nameET=(EditText)findViewById(R.id.nameET);
        balanceET=(EditText)findViewById((R.id.balanceET));
        accountLV.setOnClickListener(new  MyOnItemClickListener());
    }
    public void add(View v){
        String name=nameET.getText().toString().trim();
        String balance =balanceET.getText().toString().trim();
        Account a=new Account(name,balance, balance.equals("") ?0
                : Integer.parseInt(balance));
        dao.insert(a);
        nameET.setText("");
        balanceET.setText("");
    }
    private class MyAdapter extends BaseAdapter{

        public int getCount(){
            return list.size();
        }
        public Object getItem(int position){
            return list.get(position);
        }
        public long getItemId(int position){
            return  position;
        }
        public View getView(int position, View convertView, ViewGroup parent){
            View item=convertView!=null?convertView:View.inflate(
                    getApplicationContext(),R.layout.item,null);
            TextView idTV=(TextView) item.findViewById(R.id.idTV);
            TextView nameTV=(TextView) item.findViewById(R.id.nameTV);
            TextView balanceTV=(TextView) item.findViewById(R.id.balanceTV);
            final  Account a=list.get(position);

            idTV.setText(a.getId()+"");
            nameTV.setText(a.getName()+"");
            balanceTV.setText(a.getBalance()+"");
            ImageView upTV=(ImageView)item.findViewById(R.id.upIV);
            ImageView downTV=(ImageView)item.findViewById(R.id.downIV);
            ImageView deleteTV=(ImageView)item.findViewById(R.id.deleteIV);

            upTV.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    a.setBalance(a.getBalance()-1);
                    notifyDataSetChanged();
                    dao.updata(a);
                }
            });
            deleteTV.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    android.content.DialogInterface.OnClickListener listener=
                            new android.content.DialogInterface.OnClickListener(){
                                public  void  onClick(DialogTitle dialog,int which){
                                    list.remove(a);
                                    dao.delete(a.getId());
                                    notifyDataSetChanged();
                                }
                            };
                    Builder builder=new Builder(MainActivity.this);
                    builder.setTitle("确定要删除吗?");
                    builder.setPositiveButton("确定",listener);
                    builder.setNegativeButton("取消",null);
                    builder.show();
                }
            });
            return item;
        }
    }
    private class MyOnItemClickListener implements AdapterView.OnItemClickListener{
        public void onItemClick(AdapterView<?>parent,View view,int position,long id){
            Account a=(Account)parent.getItemAtPositon(position);
            Toast.makeText(getApplicationContext(),a.toString(),
                    Toast.LENGTH_SHORT).show();
        }
    }

运行结果如下图：