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。