商品展示

本次程序是为了通过商品展示案例结合ListView和SQLite数据库来实现在界面上操作数据库。
需要的运行效果图如下图：

1.创建程序
“商品展示”程序对应的布局文件activity_main.xml代码如下：

<?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:orientation="vertical"    tools:context="com.example.administrator.a03lab7_4.MainActivity">     <LinearLayout         android:layout_width="match_parent"         android:layout_height="wrap_content">         <EditText             android:id="@+id/etName"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:hint="商品名称"             android:inputType="text"             android:layout_weight="1"             />         <EditText             android:id="@+id/etAmount"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:hint="商品金额"             android:inputType="number"             android:layout_weight="1"             />         <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/ivGoods"        android:layout_width="match_parent"        android:layout_height="match_parent" /></LinearLayout>

2.创建ListView Item布局
在res/layout目录下创建一个item.xml文件，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">    <TextView        android:text="1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/tvId"        android:textSize="20sp"        android:layout_weight="1" />    <TextView        android:text="商品名称"        android:layout_width="0dp"        android:layout_height="wrap_content"        android:gravity="left"        android:id="@+id/tvName"        android:textSize="20sp"        android:layout_weight="2" />    <TextView        android:text="商品金额"        android:gravity="left"        android:layout_width="0dp"        android:layout_height="wrap_content"        android:id="@+id/tvAmount"        android:maxLines="1"        android:textSize="20sp"        android:layout_weight="2" />    <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="25dp"        android:layout_height="25dp"        android:src="@android:drawable/ic_menu_delete"/></LinearLayout>

3.创建数据库
创建一个名为db的包，并在该包下定义一个DBHelper类继承自SQLiteOpenHelper，创建数据库的代码如下：

package com.example.administrator.a03lab7_4.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, "gooods.db", null, version);    }    @Override    public void onCreate(SQLiteDatabase db) {        db.execSQL(CREATE_GOODS);    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    }}

4.创建一个名为dao的包，并在该包下定义一个GoodsDao类，具体的代码如下：

package com.example.administrator.a03lab7_4.dao;import android.content.ContentValues;import android.content.Context;import android.database.ContentObservable;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import com.example.administrator.a03lab7_4.db.DBHelper;import com.example.administrator.a03lab7_4.entity.Goods;import java.util.ArrayList;import java.util.List;/** * 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;    }}

5.创建一个名为entity的包，并在该包下定义一个GoodsAdapter类，具体的代码如下：

package com.example.administrator.a03lab7_4;import android.content.Context;import android.content.DialogInterface;import android.support.annotation.NonNull;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 com.example.administrator.a03lab7_4.dao.GoodsDao;import com.example.administrator.a03lab7_4.entity.Goods;import java.util.ArrayList;import java.util.List;/** * 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 v) {                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 dialog, int which) {                        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 v) {                goods.setAmount(goods.getAmount()-1);                goodsDao.update(goods);                notifyDataSetChanged();            }        });        viewHolder.ivDown.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                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.编写界面交互代码（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.administrator.a03lab7_4;import android.content.SharedPreferences;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 com.example.administrator.a03lab7_4.dao.GoodsDao;import com.example.administrator.a03lab7_4.entity.Goods;import java.util.List;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.ivGoods);        goodsDao=new GoodsDao(this);        goodsDao.queryAll();        goodsAdapter=new GoodsAdapter(this,R.layout.item,goodsList,goodsDao);        lvGoods.setAdapter(goodsAdapter);    }    public void addGoods(View view){        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();    }}

最终的菜单列表如下图所示：

最终运行出错，找不到具体原因。