private void displayScanResult(Intent initiatingIntent, String howDataReceived) { //Id String decodedData = initiatingIntent.getStringExtra(Datawedeentity.DATAWEDGE_INTENT_KEY_DATA); //类型 String decodeType = initiatingIntent.getStringExtra(Datawedeentity.DATAWEDGE_INTENT_KEY_DECODER); sendEPC(decodedData.replaceAll("-", "")); }

这段代码的作用是什么？

这段代码定义了一个名为displayScanResult的方法，接收两个参数：initiatingIntent和howDataReceived。该方法会根据传入的initiatingIntent获取扫描到的数据和数据类型，并将数据传递给sendEPC方法。在这个例子中，sendEPC方法会将扫描到的数据（去掉了“-”）传递给另一个方法进行处理。这段代码通常用于扫描二维码或条形码后获取数据，并对数据进行处理。

相关问题

用andriod studio写一个通讯录程序包含Activity，事件，数据库，列表组件、Intent、SharedPreference，实现添加删除操作

好的，我可以帮你解答这个问题。

首先，我们需要创建一个新的 Android 项目，并在 MainActivity.java 文件中添加以下代码：

public class MainActivity extends AppCompatActivity {
    private ListView contactsListView;
    private ArrayList<Contact> contactsList;
    private ContactAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 初始化通讯录列表
        contactsListView = findViewById(R.id.contacts_list);
        contactsList = new ArrayList<>();
        adapter = new ContactAdapter(this, contactsList);
        contactsListView.setAdapter(adapter);

        // 添加按钮点击事件
        Button addButton = findViewById(R.id.add_button);
        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, AddContactActivity.class);
                startActivityForResult(intent, 1);
            }
        });

        // 从数据库中加载通讯录列表
        loadContactsFromDatabase();
    }

    // 从数据库中加载通讯录列表
    private void loadContactsFromDatabase() {
        SQLiteDatabase db = new ContactDBHelper(this).getWritableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM contacts", null);
        if (cursor.moveToFirst()) {
            do {
                int id = cursor.getInt(cursor.getColumnIndex("id"));
                String name = cursor.getString(cursor.getColumnIndex("name"));
                String phone = cursor.getString(cursor.getColumnIndex("phone"));
                String email = cursor.getString(cursor.getColumnIndex("email"));
                Contact contact = new Contact(id, name, phone, email);
                contactsList.add(contact);
            } while (cursor.moveToNext());
        }
        cursor.close();
        db.close();
        adapter.notifyDataSetChanged();
    }

    // 添加联系人页面返回后的处理
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == 1 && resultCode == RESULT_OK) {
            String name = data.getStringExtra("name");
            String phone = data.getStringExtra("phone");
            String email = data.getStringExtra("email");

            // 将新的联系人添加到数据库中
            SQLiteDatabase db = new ContactDBHelper(this).getWritableDatabase();
            ContentValues values = new ContentValues();
            values.put("name", name);
            values.put("phone", phone);
            values.put("email", email);
            db.insert("contacts", null, values);
            db.close();

            // 将新的联系人添加到通讯录列表中
            Contact contact = new Contact(contactsList.size() + 1, name, phone, email);
            contactsList.add(contact);
            adapter.notifyDataSetChanged();
        }
    }
}

这里我们通过 ListView 和自定义的 ContactAdapter 类来展示通讯录列表，并在页面上添加一个“添加”按钮，点击后跳转到 AddContactActivity 页面，实现添加联系人的功能。

我们还需要创建一个 Contact 类来表示联系人，代码如下：

public class Contact {
    private int id;
    private String name;
    private String phone;
    private String email;

    public Contact(int id, String name, String phone, String email) {
        this.id = id;
        this.name = name;
        this.phone = phone;
        this.email = email;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getPhone() {
        return phone;
    }

    public String getEmail() {
        return email;
    }
}

接下来，我们需要创建一个 AddContactActivity 类来实现添加联系人的页面，代码如下：

public class AddContactActivity extends AppCompatActivity {
    private EditText nameEditText;
    private EditText phoneEditText;
    private EditText emailEditText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_contact);

        // 初始化输入框
        nameEditText = findViewById(R.id.name_edit_text);
        phoneEditText = findViewById(R.id.phone_edit_text);
        emailEditText = findViewById(R.id.email_edit_text);

        // 添加按钮点击事件
        Button addButton = findViewById(R.id.add_button);
        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = nameEditText.getText().toString();
                String phone = phoneEditText.getText().toString();
                String email = emailEditText.getText().toString();

                // 返回结果给 MainActivity 处理
                Intent intent = new Intent();
                intent.putExtra("name", name);
                intent.putExtra("phone", phone);
                intent.putExtra("email", email);
                setResult(RESULT_OK, intent);
                finish();
            }
        });
    }
}

这里我们通过 EditText 和一个“添加”按钮来实现输入联系人信息和提交的功能。

最后，我们还需要创建一个 ContactDBHelper 类来管理联系人数据库，代码如下：

public class ContactDBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "contacts.db";
    private static final int DATABASE_VERSION = 1;

    public ContactDBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE contacts (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, phone TEXT, email TEXT)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS contacts");
        onCreate(db);
    }
}

这里我们通过 SQLiteOpenHelper 类来管理联系人数据库，创建一个 contacts 表来存储联系人信息。

至此，我们已经完成了一个简单的通讯录程序的开发，具备了添加、删除联系人的功能。

三、简答题 1、简述如何使用 SharedPreferences 读写数据。 2、简述 Handler 消息机制的工作原理。 3、简述使用HttpURConnection访问网络的步骤。 四、编程题 1、现有两个Activity，分别为UserinfoActivity和ShowActivity，现在要从UserinfoActivity中通过一个“查看”按钮切换界面到ShowActivity，并传递如下三个参数 id=1:username="eric”;state=True，且ShowActivity使用 Toast 显示接收到的参数，请写出两个Activity中的核心代码 2、在网络接口 http://192.168.1.100:8080/news/getnewslist中提供了如下所示的JSON数组格式的返回数据:[f"id":1001,"title”:“"程序员因写代码太乱被杀害"，"detail”:"凶手是死者同事，维护死者代码时完全看不懂而痛下杀手":"comment" 16359,"image”:"http://192.168.1.100:8080/news/images/6.jpg) 请编写程序，访问该接口获取数据，解析后将数据显示到界面的控件上，同时将数据保存到本地的SQLite 数据库中。

三、简答题
1、使用SharedPreferences读写数据的步骤：
① 获取SharedPreferences对象：SharedPreferences sharedPreferences = getSharedPreferences("name", Context.MODE_PRIVATE);
② 获取SharedPreferences.Editor对象：SharedPreferences.Editor editor = sharedPreferences.edit();
③ 写入数据：editor.putString("key", value);
④ 提交数据：editor.commit();
⑤ 读取数据：sharedPreferences.getString("key", defaultValue);

2、Handler消息机制的工作原理：
Handler是Android中消息机制的基础，它可以实现不同线程之间的通信。Handler包括两个主要部分：消息队列和消息处理器。消息队列是一个存储消息的FIFO队列，消息处理器则是用来处理消息的对象。当Handler创建时，它会自动与当前线程的消息队列关联起来。当调用Handler的sendMessage()方法，会向消息队列中添加一条消息。当Handler处理消息时，会从消息队列中取出一条消息，交给消息处理器处理，如果消息处理器处理完消息后需要更新UI，可以使用Handler的post()或者postDelayed()方法将消息发送到UI线程中执行。

3、使用HttpURLConnection访问网络的步骤：
① 创建URL对象：URL url = new URL("http://www.example.com");
② 打开URLConnection连接：HttpURLConnection connection = (HttpURLConnection) url.openConnection();
③ 设置请求方式：connection.setRequestMethod("GET");
④ 设置连接超时时间：connection.setConnectTimeout(5000);
⑤ 设置读取超时时间：connection.setReadTimeout(5000);
⑥ 发送请求：connection.connect();
⑦ 获取响应码：int responseCode = connection.getResponseCode();
⑧ 获取输入流：InputStream inputStream = connection.getInputStream();
⑨ 读取数据：BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder stringBuilder = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
stringBuilder.append(line);
}
String result = stringBuilder.toString();
⑩ 关闭连接：connection.disconnect();

四、编程题
1、UserinfoActivity中的代码：

public void onClick(View view) {
    Intent intent = new Intent(UserinfoActivity.this, ShowActivity.class);
    intent.putExtra("id", 1);
    intent.putExtra("username", "eric");
    intent.putExtra("state", true);
    startActivity(intent);
}

ShowActivity中的代码：

Intent intent = getIntent();
int id = intent.getIntExtra("id", 0);
String username = intent.getStringExtra("username");
boolean state = intent.getBooleanExtra("state", false);
Toast.makeText(ShowActivity.this, "id=" + id + " username=" + username + " state=" + state, Toast.LENGTH_SHORT).show();

2、代码如下：

public void getData() {
    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                URL url = new URL("http://192.168.1.100:8080/news/getnewslist");
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.setConnectTimeout(5000);
                connection.setReadTimeout(5000);
                connection.connect();
                int responseCode = connection.getResponseCode();
                if (responseCode == HttpURLConnection.HTTP_OK) {
                    InputStream inputStream = connection.getInputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
                    StringBuilder stringBuilder = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        stringBuilder.append(line);
                    }
                    String result = stringBuilder.toString();
                    Gson gson = new Gson();
                    List<News> newsList = gson.fromJson(result, new TypeToken<List<News>>(){}.getType());
                    for (News news : newsList) {
                        // 将数据保存到SQLite数据库中
                        dbHelper.insertNews(news.getId(), news.getTitle(), news.getDetail(), news.getComment(), news.getImage());
                    }
                    // 更新UI
                    Message message = Message.obtain();
                    message.what = UPDATE_UI;
                    message.obj = newsList;
                    handler.sendMessage(message);
                    reader.close();
                    inputStream.close();
                }
                connection.disconnect();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();
}

private void updateUI(List<News> newsList) {
    // 将数据显示到界面的控件上
}

// News类
public class News {
    private int id;
    private String title;
    private String detail;
    private int comment;
    private String image;

    public News(int id, String title, String detail, int comment, String image) {
        this.id = id;
        this.title = title;
        this.detail = detail;
        this.comment = comment;
        this.image = image;
    }

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getDetail() {
        return detail;
    }

    public int getComment() {
        return comment;
    }

    public String getImage() {
        return image;
    }
}

// DBHelper类
public class DBHelper extends SQLiteOpenHelper {

    private static final String DB_NAME = "news.db";
    private static final int DB_VERSION = 1;
    private static final String TABLE_NAME = "news";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_TITLE = "title";
    private static final String COLUMN_DETAIL = "detail";
    private static final String COLUMN_COMMENT = "comment";
    private static final String COLUMN_IMAGE = "image";
    private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + " (" +
            COLUMN_ID + " INTEGER PRIMARY KEY, " +
            COLUMN_TITLE + " TEXT, " +
            COLUMN_DETAIL + " TEXT, " +
            COLUMN_COMMENT + " INTEGER, " +
            COLUMN_IMAGE + " TEXT)";

    public DBHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }

    public void insertNews(int id, String title, String detail, int comment, String image) {
        SQLiteDatabase db = getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_ID, id);
        values.put(COLUMN_TITLE, title);
        values.put(COLUMN_DETAIL, detail);
        values.put(COLUMN_COMMENT, comment);
        values.put(COLUMN_IMAGE, image);
        db.insert(TABLE_NAME, null, values);
        db.close();
    }

    public List<News> getNewsList() {
        List<News> newsList = new ArrayList<>();
        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM " + TABLE_NAME, null);
        if (cursor.moveToFirst()) {
            do {
                int id = cursor.getInt(cursor.getColumnIndex(COLUMN_ID));
                String title = cursor.getString(cursor.getColumnIndex(COLUMN_TITLE));
                String detail = cursor.getString(cursor.getColumnIndex(COLUMN_DETAIL));
                int comment = cursor.getInt(cursor.getColumnIndex(COLUMN_COMMENT));
                String image = cursor.getString(cursor.getColumnIndex(COLUMN_IMAGE));
                News news = new News(id, title, detail, comment, image);
                newsList.add(news);
            } while (cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return newsList;
    }
}

// Handler类
private static final int UPDATE_UI = 1;
private Handler handler = new Handler(new Handler.Callback() {
    @Override
    public boolean handleMessage(@NonNull Message message) {
        switch (message.what) {
            case UPDATE_UI:
                List<News> newsList = (List<News>) message.obj;
                updateUI(newsList);
                break;
        }
        return false;
    }
});