商品展示案例

1.创建程序

首先创建一个名为”商品展示“的应用程序，将包名修改为cn.edu.bzu.shopshowdemo。设计用户交互页面。

"商品展示"程序对应的布局文件（activity_main.xml）如下所示:

2.创建ListView Item布局

由于本案例用到ListView布局，因此需要编写一个ListView Item的布局。在res/layout目录下创建一个item.xml文件：

3.创建数据库

创建数据库属于数据操作，因此需要在cn.edu.bzu.shopshowdemo的包下创建一个名为db的包，并在该包下定义一个DBhelper类继承自SQLOpenHelper。创建的数据库如下：

4.创建数据操作逻辑类

在cn.edu.bzu.shopshowdemo包下创建一个GoodsDao类用于操作数据，如下所示：

5.创建GoodsAdapter.java,如下图：

6.编写交互代码（MainActivity）

数据库的操作完成之后需要界面与数据库进行交互，用于实现数据库中的数据以ListView的形式展示在页面上，如下所示：

7.运行程序展示商品

添加：

删除：

增加金额：

减少金额：

代码如下：

1.activity_main.xml布局文件中的代码：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context="cn.edu.bzu.shopshowdemo.MainActivity">    <LinearLayout        android:id="@+id/addLL"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:orientation="horizontal">        <EditText            android:id="@+id/etName"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_weight="1"            android:hint="商品名称"            android:inputType="text" />        <EditText            android:id="@+id/etAmount"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_weight="1"            android:hint="商品金额"            android:inputType="number" />        <ImageView            android:id="@+id/ivAdd"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:onClick="addGoods"            android:src="@android:drawable/ic_input_add" />    </LinearLayout>    <ListView        android:id="@+id/lvGoods"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:layout_below="@+id/addLL"></ListView></RelativeLayout>

2.items.xml布局文件中的代码：

<?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">    <TextView        android:id="@+id/tvId"        android:layout_width="0dp"        android:layout_height="wrap_content"        android:layout_weight="2"        android:gravity="left"        android:text="1"        android:textSize="20sp" />    <TextView        android:id="@+id/tvName"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_weight="1"        android:gravity="left"        android:maxLines="1"        android:text="商品名称"        android:textSize="20sp" />    <TextView        android:id="@+id/tvAmount"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_weight="2"        android:gravity="left"        android:maxLines="1"        android:text="金额"        android:textSize="20sp" />    <LinearLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:orientation="vertical">        <ImageView            android:id="@+id/ivUp"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:src="@android:drawable/arrow_up_float" />        <ImageView            android:id="@+id/ivDown"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:src="@android:drawable/arrow_down_float" />    </LinearLayout>    <ImageView        android:id="@+id/ivDelete"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:src="@android:drawable/ic_menu_delete" /></LinearLayout>


3.GoodsDao类中的文件代码：

package cn.edu.bzu.shopshowdemo.dao;import android.content.ContentValues;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.widget.Toast;import java.util.ArrayList;import java.util.List;import cn.edu.bzu.shopshowdemo.db.DBhelper;import cn.edu.bzu.shopshowdemo.entity.Goods;/** * Created by Administrator on 2017/4/27. */public class GoodsDao {    private DBhelper dBhelper;    public GoodsDao(Context context) {        dBhelper = new DBhelper(context, 1);    }    public void add(Goods goods) {        SQLiteDatabase sqLiteDatabase = dBhelper.getWritableDatabase();        ContentValues values = new ContentValues();        values.put("name", goods.getName());        values.put("amount", goods.getAmount());       long id= sqLiteDatabase.insert("goods", null, values);        goods.setId(id);        sqLiteDatabase.close();    }    public int delete(long id) {        SQLiteDatabase sqLiteDatabase = dBhelper.getWritableDatabase();        int count = sqLiteDatabase.delete("goods", "_id=?", new String[]{id + ""});        sqLiteDatabase.close();        return count;    }    public int update(Goods goods) {        SQLiteDatabase sqLiteDatabase = dBhelper.getWritableDatabase();        ContentValues values = new ContentValues();        values.put("name", goods.getName());        values.put("amount", goods.getAmount());        int count = sqLiteDatabase.update("goods", values, "_id=?", new String[]{goods.getId() + ""});        sqLiteDatabase.close();        return count;    }    public List<Goods> queryALL() {        List<Goods> goodsList = new ArrayList<>();        SQLiteDatabase sqLiteDatabase = dBhelper.getReadableDatabase();        Cursor cursor = sqLiteDatabase.query("goods", null, null, null, null, null, "amount desc");        while (cursor.moveToNext()) {            long id = cursor.getLong(cursor.getColumnIndex("_id"));            String name = cursor.getString(cursor.getColumnIndex("name"));            int amount = cursor.getInt(cursor.getColumnIndex("amount"));            Goods goods = new Goods(id,name,amount);            goodsList.add(goods);        }        cursor.close();        sqLiteDatabase.close();        return goodsList;    }}

4.DBhelper.java文件中的程序代码：

package cn.edu.bzu.shopshowdemo.db;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;/** * Created by Administrator on 2017/4/27. */public class DBhelper extends SQLiteOpenHelper{    public static final  String CREATE_GOODS="create table goods(_id integer primary key autoincrement,name varchar(20),amount integer)";    public DBhelper(Context context,  int version) {        super(context, "goods.db", null, version);    }    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL(CREATE_GOODS);    }    @Override    public void onUpgrade(SQLiteDatabase db, int i, int i1) {    }}

5.GoodsAdapter.java文件中的程序代码：

package cn.edu.bzu.shopshowdemo;import android.content.Context;import android.content.DialogInterface;import android.preference.DialogPreference;import android.support.annotation.NonNull;import android.support.annotation.PluralsRes;import android.support.v7.app.AlertDialog;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.ImageView;import android.widget.TextView;import java.util.List;import cn.edu.bzu.shopshowdemo.dao.GoodsDao;import cn.edu.bzu.shopshowdemo.entity.Goods;/** * Created by Administrator on 2017/4/27. */public class GoodsAdapter extends ArrayAdapter<Goods>{    private int resounceId;    private GoodsDao goodsDao;    private List<Goods> goodsList;    public GoodsAdapter(Context context, int resource, List<Goods> objects, GoodsDao goodsDao) {        super(context, resource, objects);        resounceId=resource;        goodsList =objects;        this.goodsDao=goodsDao;    }    @NonNull    @Override    public View getView(int position, View convertView, ViewGroup parent) {        final Goods goods=getItem(position);        View view =null;        ViewHolder viewHolder;        if(convertView==null){            view=LayoutInflater.from(getContext()).inflate(resounceId,null);            viewHolder=new ViewHolder();            viewHolder.tvId= (TextView) view.findViewById(R.id.tvId);            viewHolder.tvName= (TextView) view.findViewById(R.id.tvName);            viewHolder.tvAmount= (TextView) view.findViewById(R.id.tvAmount);            viewHolder.ivUp= (ImageView) view.findViewById(R.id.ivUp);            viewHolder.ivDown= (ImageView) view.findViewById(R.id.ivDown);            viewHolder.ivDelete= (ImageView) view.findViewById(R.id.ivDelete);            view.setTag(viewHolder);        }else{            view =convertView;            viewHolder= (ViewHolder) view.getTag();        }        viewHolder.tvId.setText(goods.getId()+"");        viewHolder.tvName.setText(goods.getName());        viewHolder.tvAmount.setText(goods.getAmount()+"");        viewHolder.ivDelete.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                AlertDialog.Builder builder=new AlertDialog.Builder(getContext());                builder.setTitle("你确定要删除吗？");                builder.setPositiveButton("yes", new DialogInterface.OnClickListener() {                    @Override                    public void onClick(DialogInterface dialogInterface, int i) {                        goodsList.remove(goods);                        goodsDao.delete(goods.getId());                        notifyDataSetChanged();                    }                });                builder.setNegativeButton("cancel",null);                builder.show();            }        });        viewHolder.ivUp.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                goods.setAmount(goods.getAmount()-1);                goodsDao.update(goods);                notifyDataSetChanged();            }        });        viewHolder.ivDown.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                goods.setAmount(goods.getAmount()+1);                goodsDao.update(goods);                notifyDataSetChanged();            }        });        return view;    }    class ViewHolder{        TextView tvId;        TextView tvName;        TextView tvAmount;        ImageView ivUp;        ImageView ivDown;        ImageView ivDelete;    }}

6.MainActivity.java中的文件代码：

package cn.edu.bzu.shopshowdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.text.TextUtils;import android.view.View;import android.widget.EditText;import android.widget.ListView;import android.widget.Toast;import java.util.List;import cn.edu.bzu.shopshowdemo.dao.GoodsDao;import cn.edu.bzu.shopshowdemo.entity.Goods;public class MainActivity extends AppCompatActivity {    private EditText etName;    private EditText etAmount;    private ListView lvGoods ;    private GoodsAdapter goodsAdapter;    private GoodsDao goodsDao;    private List<Goods> goodsList;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        etName= (EditText) findViewById(R.id.etName);        etAmount= (EditText) findViewById(R.id.etAmount);        lvGoods = (ListView) findViewById(R.id.lvGoods);        goodsDao = new GoodsDao(this);       goodsList= goodsDao.queryALL();        goodsAdapter =new GoodsAdapter(this,R.layout.item,goodsList,goodsDao);        lvGoods.setAdapter(goodsAdapter);    }    public void addGoods(View view){        Toast.makeText(this,"添加成功",Toast.LENGTH_LONG).show();        String name =etName.getText().toString();        String amount = etAmount.getText().toString();        if(TextUtils.isEmpty(name)||TextUtils.isEmpty(amount))            return;        Goods goods = new Goods(name,Integer.parseInt(amount));        goodsDao.add(goods);        goodsList.add(goods);        goodsAdapter.notifyDataSetChanged();        etName.setText("");        etAmount.setText("");        Toast.makeText(this,"添加成功",Toast.LENGTH_LONG).show();    }}

出现的问题：

delete按钮与up、down按钮不处于同一水平位置？

解决方案：

将delete按钮放在up、down按钮线性布局的外面