商品展示案例



1.创建程序

首先创建一个商品展示的布局文件，代码如下所示：

<?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_shang"    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="bzu.edu.cn.a17lab08.ShangActivity">    <LinearLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:orientation="horizontal"        android:id="@+id/ii1"        ><EditText    android:layout_width="150dp"    android:layout_height="wrap_content"    android:hint="商品名称"    android:layout_weight="2"    android:id="@+id/e1"    android:inputType="textPersonName"/>        <EditText            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:hint="金额"            android:layout_marginRight="80dp"            android:layout_weight="1"            android:id="@+id/e2"            android:inputType="number"           />        <ImageView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:onClick="add"            android:id="@+id/i1"            android:src="@android:drawable/ic_input_add"           />    </LinearLayout>    <ListView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/l1"        android:layout_below="@id/ii1">

    </ListView></RelativeLayout>

上述代码中ImageView有一些系统自定义的，直接可以使用。

2.创建一个ListView Item布局

此布局文件主要对Item进行布局调整，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:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="1"    android:textColor="#000000"    android:layout_weight="1"    android:textSize="20sp"    android:id="@+id/t1"/>    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="毛巾"        android:textColor="#000000"        android:layout_weight="2"        android:textSize="20sp"        android:id="@+id/t2"/>    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="20"        android:textColor="#000000"        android:layout_weight="2"        android:textSize="20sp"        android:id="@+id/t3"/>    <LinearLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:orientation="vertical">        <ImageView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:id="@+id/addup"            android:src="@android:drawable/arrow_up_float"            android:layout_marginBottom="2dp"/>        <ImageView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:id="@+id/adddown"            android:src="@android:drawable/arrow_down_float"            android:layout_marginBottom="2dp"/>    </LinearLayout>    <ImageView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/delete"        android:src="@android:drawable/ic_menu_delete"/></LinearLayout>

3.创建数据库

创建数据库属于数据操作，因此需要在包下再创建一个名为dao的包，并在该包下定义一个MyHelper类继承自SQLiteOpenHelper，创建数据库的代码如下：

package bzu.edu.cn.a17lab08.dao;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;import android.provider.Settings;public class MyHelper extends SQLiteOpenHelper {    public MyHelper(Context context){        super(context,"edu.db",null,2);    }    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 sqLiteDatabase, int oldVersion, int newVersion) {        System.out.println("onUpgrade");    }}

4.创建Account类

在操作数据库时将数据存放至一个JavaBean对象中操作起来会比较方便。因此需要在包下创建一个bean包存放JavaBean类然后包下创建一个Account类，代码如下：

package bzu.edu.cn.a17lab08.bean;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(Long 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+",金额："+balance+"]";    }}

5.创建数据操作逻辑类

前面创建了数据库和JavaBean，接下来需要编写数据逻辑操作类。在包下创建一个AccountDao类用于操作数据。具体代码如下：

package bzu.edu.cn.a17lab08.dao;import android.content.ContentValues;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import java.util.ArrayList;import java.util.List;import bzu.edu.cn.a17lab08.bean.Account;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 update(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;        db = helper.getWritableDatabase();        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;    }}

该类创建了对数据进行增删改查操作的方法。在当中db.insert()方法调用了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

想插入一条空数据，第二个参数必须写一个列名，传入这个列名是用来拼接SQL语句的，例如，INSERT INTO account(null)VALUES(NULL).

6.编写界面交互代码

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，代码如下：

package bzu.edu.cn.a17lab08;import android.content.DialogInterface;import android.support.v7.app.AlertDialog;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;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 java.util.List;import bzu.edu.cn.a17lab08.dao.AccountDao;import bzu.edu.cn.a17lab08.bean.Account;public class ShangActivity extends AppCompatActivity {    private List<Account> list;    private AccountDao dao;    private EditText e1;    private EditText e2;    private MyAdapter adapter;    private ListView lv;    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_shang);        initView();        dao = new AccountDao(this);        list=dao.queryAll();        adapter = new MyAdapter();        lv.setAdapter(adapter);    }    private void initView(){        lv = (ListView) findViewById(R.id.l1);        e1 = (EditText) findViewById(R.id.e1);        e2 = (EditText) findViewById(R.id.e2);        lv.setOnItemClickListener(new MyOnItemClickListener());    }    public void add(View v) {        String name = e1.getText().toString().trim();        String balance = e2.getText().toString().trim();        Account a = new Account(name, balance.equals("") ?0 : Integer.parseInt(balance));        dao.insert(a);        list.add(a);        adapter.notifyDataSetChanged();        lv.setSelection(lv.getCount() - 1);        e1.setText("");        e2.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 t1 = (TextView) item.findViewById(R.id.t1);            TextView t2 = (TextView) item.findViewById(R.id.t2);            TextView t3 = (TextView) item.findViewById(R.id.t3);            final Account a = list.get(position);            t1.setText(a.getId() + "");            t2.setText(a.getName());            t3.setText(a.getBalance() + "");            ImageView up = (ImageView) item.findViewById(R.id.addup);            ImageView down = (ImageView) item.findViewById(R.id.adddown);            ImageView delete = (ImageView) item.findViewById(R.id.delete);            up.setOnClickListener(new View.OnClickListener() {                public void onClick(View v) {                    a.setBalance(a.getBalance() - 1);                    notifyDataSetChanged();                    dao.update(a);                }            });            down.setOnClickListener(new View.OnClickListener() {                public void onClick(View v) {                    a.setBalance(a.getBalance() - 1);                    notifyDataSetChanged();                    dao.update(a);                }                });            delete.setOnClickListener(new View.OnClickListener() {                public void onClick(View v) {                    final DialogInterface.OnClickListener listener = new android.content.DialogInterface.OnClickListener() {                        public void onClick(DialogInterface dialog, int which) {                            list.remove(a);                            dao.delete(a.getId());                            notifyDataSetChanged();                        }                    };                    AlertDialog.Builder builder = new AlertDialog.Builder(ShangActivity.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.getItemAtPosition(position);            Toast.makeText(getApplicationContext(),a.toString(),Toast.LENGTH_SHORT).show();    }}}
《商品展示》的基本代码已经完成。效果图如下：