Android-商品展示案例

1.创建程序

创建一个名为“商品展示”的应用程序，将包名修改为cn.edu.bzu。

2.用户交互界面

（1）“商品展示”程序对应的布局文件（activity_main.xml）

线性布局下包含一个水平显示的线性布局和一个ListView控件垂直显示；在水平显示的线性布局（LinearLayout）下建两个文本控件（EditText）“商品名称”、“金额”和一个显示图片控件。文本属性Android:inputType其中使用到了ImageView的属性Android:src来指定ImageView要显示的图片，但是只显示图片原图大小；如果使用Android:src属性，图片的大小会根据ImageView的大小进行拉伸。此外，ListView控件以列表的形式展示具体数据的内容，并且能够根据数据的长度自适应屏幕的显示。例：

<?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"    android:layout_margin="8dp"    tools:context="cn.edu.bzu.showproduct.MainActivity"><LinearLayout    android:id="@+id/addLL"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:orientation="horizontal">    <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:onClick="add"        android:layout_width="30dp"        android:layout_height="32dp"        android:src="@drawable/input" /></LinearLayout>    <ListView        android:id="@+id/accoutLV"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:layout_below="@id/addLL">    </ListView></LinearLayout>

（2）ListView Item 布局（item.xml）

用到了ListView布局，故要编写一个ListView itemd的布局。在res/layout目录下建一个item.xml文件，该文件有三个TextView文本控件，分别用于显示数据库中的某条数据的id、商品名称、金额和三个ImageView图片控件用于增加、减少金额，删除数据。例：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="horizontal"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:padding="10dp">    <TextView        android:id="@+id/idTV"        android:layout_width="0dp"        android:layout_height="wrap_content"        android:layout_weight="1"        android:text="1"        android:textColor="@color/colorAccent"        android:textSize="20sp"/>    <TextView        android:id="@+id/nameTV"        android:layout_width="0dp"        android:layout_height="wrap_content"        android:layout_weight="2"        android:text="PQ"        android:textColor="@color/colorAccent"        android:textSize="20sp"/>    <TextView        android:id="@+id/balanceTV"        android:layout_width="0dp"        android:layout_height="wrap_content"        android:layout_weight="2"        android:text="12345"        android:textColor="@color/colorAccent"        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="18dp"            android:layout_height="18dp"            android:layout_marginBottom="2dp"            android:src="@drawable/up"/>        <ImageView            android:id="@+id/downIV"            android:layout_width="18dp"            android:layout_height="18dp"            android:src="@drawable/down"/>    </LinearLayout>    <ImageView        android:id="@+id/deleteIV"        android:layout_width="28dp"        android:layout_height="40dp"        android:src="@drawable/delete"/></LinearLayout>

3.创建数据库

数据库操作，在cn.itcast.product的包下创建一个名为dao 的包并在其下定义一个MyHelp类继承自SQLiteOpenHelper,代码如下：

public class MyHelper extends SQLiteOpenHelper {    public MyHelper(Context context){        super(context,"itcast.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)");    }    public  void  onUpgrade(SQLiteDatabase db,int oldVersion,int newViersion){        System.out.println("onUpgrade");    }}

4.Account类

该类主要是创建JavaBean对象，用来存放操作数据库时的数据。在cn.itcast.product创建一个bean包存放JavaBean类，然后在cn.itcast.product.bean包下定义一个类Accout,代码如下：

package cn.edu.bzu.showproduct.bean;/** * Created by Administrator on 2017/5/4. */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+",余额:"+balance+"]";    }}

5.创建数据操作逻辑类

在cn.itcast.product.dao包下建AccountDao类用于对数据进行增、删、改、查操作方法。

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，如果想插入一条空数据，第二个参数必须写一个列名，用来拼接SQL语句。

代码如下：

package cn.edu.bzu.showproduct.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 cn.edu.bzu.showproduct.bean.Account;/** * Created by Administrator on 2017/5/4. */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 valuse=new ContentValues();        valuse.put("name",account.getName());        valuse.put("balance",account.getBalance());        int count=db.update("account",valuse,"_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;    }}

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 cn.edu.bzu.showproduct;import android.content.DialogInterface;import android.net.Uri;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.view.ViewGroup;import android.widget.Adapter;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.google.android.gms.appindexing.Action;import com.google.android.gms.appindexing.AppIndex;import com.google.android.gms.appindexing.Thing;import com.google.android.gms.common.api.GoogleApiClient;import org.w3c.dom.Text;import java.util.List;import cn.edu.bzu.showproduct.R;import cn.edu.bzu.showproduct.bean.Account;import cn.edu.bzu.showproduct.dao.AccountDao;import cn.edu.bzu.showproduct.dao.MyHelper;public class MainActivity extends AppCompatActivity {    private List<Account> list;    private AccountDao dao;    private EditText nameET;    private EditText balanceET;    private MyAdapter adapter;    private ListView accountLV;    /**     * ATTENTION: This was auto-generated to implement the App Indexing API.     * See https://g.co/AppIndexing/AndroidStudio for more information.     */    private GoogleApiClient client;    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);        // ATTENTION: This was auto-generated to implement the App Indexing API.        // See https://g.co/AppIndexing/AndroidStudio for more information.        client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();    }    private void initView() {        accountLV = (ListView) findViewById(R.id.accoutLV);        nameET = (EditText) findViewById(R.id.nameET);        balanceET = (EditText) findViewById(R.id.balanceET);        accountLV.setOnItemClickListener((AdapterView.OnItemClickListener) 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.equals("") ? 0 : Integer.parseInt(balance));        dao.insert(a);        list.add(a);        adapter.notifyDataSetChanged();        accountLV.setSelection(accountLV.getCount() - 1);        nameET.setText("");        balanceET.setText("");    }    /**     * ATTENTION: This was auto-generated to implement the App Indexing API.     * See https://g.co/AppIndexing/AndroidStudio for more information.     */    public Action getIndexApiAction() {        Thing object = new Thing.Builder()                .setName("Main Page") // TODO: Define a title for the content shown.                // TODO: Make sure this auto-generated URL is correct.                .setUrl(Uri.parse("http://[ENTER-YOUR-URL-HERE]"))                .build();        return new Action.Builder(Action.TYPE_VIEW)                .setObject(object)                .setActionStatus(Action.STATUS_TYPE_COMPLETED)                .build();    }    @Override    public void onStart() {        super.onStart();        // ATTENTION: This was auto-generated to implement the App Indexing API.        // See https://g.co/AppIndexing/AndroidStudio for more information.        client.connect();        AppIndex.AppIndexApi.start(client, getIndexApiAction());    }    @Override    public void onStop() {        super.onStop();        // ATTENTION: This was auto-generated to implement the App Indexing API.        // See https://g.co/AppIndexing/AndroidStudio for more information.        AppIndex.AppIndexApi.end(client, getIndexApiAction());        client.disconnect();    }    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 upIV = (ImageView) item.findViewById(R.id.upIV);            ImageView downIV = (ImageView) item.findViewById(R.id.downIV);            ImageView deleteIV = (ImageView) item.findViewById(R.id.deleteIV);            upIV.setOnClickListener(new View.OnClickListener() {                @Override                public void onClick(View v) {                    a.setBalance(a.getBalance() + 1);                    notifyDataSetChanged();                    dao.update(a);                }            });            downIV.setOnClickListener(new View.OnClickListener() {                @Override                public void onClick(View v) {                    a.setBalance(a.getBalance() - 1);                    notifyDataSetChanged();                    dao.update(a);                }            });            deleteIV.setOnClickListener(new View.OnClickListener() {                @Override                public void onClick(View v) {                    DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {                        public void onClick(DialogInterface 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 DialogInterface.OnClickListener {        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();        }    }}

7.运行程序

（1）“商品展示”界面；

（2）在提示“商品名称”和“金额”上的文本框中输入姓名和金额后单击“添加”按钮，添加数据至数据库并显示适配器到ListView中；

（3）单击条目的向上按钮，对应的金额将会增加，单击向下按钮，金额会减少；

（4）单击删除按钮，会弹出一个对话框，单击对话框的确认按钮就将第二条数据删除了；

（5）单击条目会弹出一个Toast,要实现该功能需要给ListView的item设置条目点击监听事件。