HarmonyOS基础技术赋能之轻量级数据库Preferencens-轻量级数据库开发框架

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引言

轻量级数据存储适用于对Key-Value结构的数据进行存取和持久化操作。主要用于保存应用的一些常用配置，并不适合存储大量数据和频繁改变数据的场景。用户的数据保存在文件中，可以持久化的存储在设备上。需要注意的是用户访问的实例包含文件所有数据，并一直加载在设备的内存中，并通过轻量级数据存储的API完成数据操作。

功能介绍

轻量级数据存储向本地应用提供的API支持本地应用读写数据及观察数据变化。数据存储形式为键值对，键的类型为字符串型(String)，值的存储数据类型包括整型(int)、字符串型(String)、布尔型(boolean)、浮点型(float)、长整型(long)、字符串型Set集合(Set)。

开发指南

1. 创建Preferences实例。

// context为上下文对象，PREFERENCE_FILE_NAME为轻量级数据库文件名，String类型，可以自定义 
databaseHelper = new DatabaseHelper(context); 
preferences = databaseHelper.getPreferences(PREFERENCE_FILE_NAME);

2. 将数据写入指定文件。

// preferences.putString()为存入String类型的数据 
preferences.putString(String key, String value); 
// flush()为异步持久化数据；flushSync()为同步持久化数据 
preferences.flush()/preferences.flushSync();

3.从指定文件读取数据。

//读取时传入的key, 要与写入时传入的key一致，才能获取对应数据，第二个参数为默认值。 
  preferences.getString(String key, String default)

4. 开发者可以向Preferences实例注册观察者，观察数据更新变化。

private class PreferencesObserverImpl implements Preferences.PreferencesObserver { 
    
    @Override     
    public void onChange(Preferences preferences, String key) { 
        if ("key".equals(key)) { 
           HiLog.info(LABLE, "Change Received：[key=value]");         
        }     
    } 
} 
 
 
// 向preferences实例注册观察者 
PreferencesObserverImpl observer = new PreferencesObserverImpl(); 
preferences.registerObserver(observer); 
// 修改数据后，observer的onChange方法会被回调 
// 向preferences实例注销观察者 
preferences.unRegisterObserver(observer);

源码如下：

1.PreferenceUtils

public class PreferenceUtils { 
 
  private static String PREFERENCE_FILE_NAME = "prefrence_file"; 
  private static Preferences preferences; 
  private static DatabaseHelper databaseHelper; 
  private static PreferencesObserver mPreferencesObserver; 
 
  private static void initPreference(Context context){ 
    if(databaseHelper==null){ 
      databaseHelper = new DatabaseHelper(context); 
    } 
    if(preferences==null){ 
      preferences = databaseHelper.getPreferences(PREFERENCE_FILE_NAME); 
    } 
 
  } 
 
  //存放、获取时传入的context必须是同一个context,否则存入的数据无法获取 
  public static void putString(Context context, String key, String value) { 
    initPreference(context); 
    preferences.putString(key, value); 
    preferences.flush(); 
  } 
 
  /** 
   * @param context 上下文 
   * @param key  键 
   * @return 获取的String 默认值为:null 
   */ 
  public static String getString(Context context, String key) { 
    initPreference(context); 
    return preferences.getString(key, null); 
  } 
 
 
  public static void putInt(Context context, String key, int value) { 
    initPreference(context); 
    preferences.putInt(key, value); 
    preferences.flush(); 
  } 
 
  /** 
   * @param context 上下文 
   * @param key 键 
   * @return 获取int的默认值为：-1 
   */ 
  public static int getInt(Context context, String key) { 
    initPreference(context); 
    return preferences.getInt(key, -1); 
  } 
 
 
  public static void putLong(Context context, String key, long value) { 
    initPreference(context); 
    preferences.putLong(key, value); 
    preferences.flush(); 
  } 
 
  /** 
   * @param context 上下文 
   * @param key  键 
   * @return 获取long的默认值为：-1 
   */ 
  public static long getLong(Context context, String key) { 
    initPreference(context); 
    return preferences.getLong(key, -1L); 
  } 
 
 
  public static void putBoolean(Context context, String key, boolean value) { 
    initPreference(context); 
    preferences.putBoolean(key, value); 
    preferences.flush(); 
  } 
 
  /** 
   * @param context  上下文 
   * @param key  键 
   * @return 获取boolean的默认值为：false 
   */ 
  public static boolean getBoolean(Context context, String key) { 
    initPreference(context); 
    return preferences.getBoolean(key, false); 
  } 
 
 
  public static void putFloat(Context context, String key, float value) { 
    initPreference(context); 
    preferences.putFloat(key, value); 
    preferences.flush(); 
  } 
 
  /** 
   * @param context 上下文 
   * @param key   键 
   * @return 获取float的默认值为：0.0 
   */ 
  public static float getFloat(Context context, String key) { 
    initPreference(context); 
    return preferences.getFloat(key, 0.0F); 
  } 
 
 
  public static void putStringSet(Context context, String key, Set<String> set) { 
    initPreference(context); 
    preferences.putStringSet(key, set); 
    preferences.flush(); 
  } 
 
  /** 
   * @param context  上下文 
   * @param key 键 
   * @return 获取set集合的默认值为：null 
   */ 
  public static Set<String> getStringSet(Context context, String key) { 
    initPreference(context); 
    return preferences.getStringSet(key, null); 
  } 
 
 
  public static boolean deletePreferences(Context context) { 
    initPreference(context); 
    boolean isDelete= databaseHelper.deletePreferences(PREFERENCE_FILE_NAME); 
    return isDelete; 
  } 
 
 
  public static void registerObserver(Context context,PreferencesObserver preferencesObserver){ 
    initPreference(context); 
    mPreferencesObserver=preferencesObserver; 
    preferences.registerObserver(mPreferencesObserver); 
  } 
 
  public static void unregisterObserver(){ 
    if(mPreferencesObserver!=null){ 
      // 向preferences实例注销观察者 
      preferences.unregisterObserver(mPreferencesObserver); 
    } 
  } 
 
}

2. MainAbilitySlice

public class MainAbilitySlice extends AbilitySlice implements ClickedListener { 
  private TextField tfName; 
  private TextField tfGener; 
  private TextField tfAge; 
  private TextField tfWeight; 
  private Text tvResultQuery; 
  private Text tvResultListener; 
  private String name; 
  private boolean isMan; 
  private int age; 
  private float weight; 
 
 
  @Override 
  public void onStart(Intent intent) { 
    super.onStart(intent); 
    super.setUIContent(ResourceTable.Layout_ability_main); 
    tfName=(TextField)findComponentById(ResourceTable.Id_tf_name); 
    tfGener=(TextField)findComponentById(ResourceTable.Id_tf_isMan); 
    tfAge=(TextField)findComponentById(ResourceTable.Id_tf_age); 
    tfWeight=(TextField)findComponentById(ResourceTable.Id_tf_weight); 
    tvResultQuery=(Text) findComponentById(ResourceTable.Id_tvResultQuery); 
    tvResultListener=(Text) findComponentById(ResourceTable.Id_tvResultListener); 
    Button btSave=(Button)findComponentById(ResourceTable.Id_bt_save); 
    Button btQuery=(Button)findComponentById(ResourceTable.Id_bt_query); 
    Button btRegister=(Button)findComponentById(ResourceTable.Id_bt_regist); 
    Button btUnRegister=(Button)findComponentById(ResourceTable.Id_bt_unregist); 
    btSave.setClickedListener(this); 
    btQuery.setClickedListener(this); 
    btRegister.setClickedListener(this); 
    btUnRegister.setClickedListener(this); 
  } 
 
  @Override 
  public void onActive() { 
    super.onActive(); 
  } 
 
  @Override 
  public void onForeground(Intent intent) { 
    super.onForeground(intent); 
  } 
 
  @Override 
  public void onClick(Component component) { 
    switch (component.getId()){ 
      case ResourceTable.Id_bt_save: 
        PreferenceUtils.putString(MyApplication.mContext,"name",tfName.getText()); 
        if(tfGener.getText().equals("男")){ 
          PreferenceUtils.putBoolean(MyApplication.mContext,"gender",true); 
        } 
        try { 
          String age=tfAge.getText(); 
          String weight=tfWeight.getText(); 
          int ageInt=Integer.parseInt(age); 
          float weightFloat=Float.parseFloat(weight); 
          PreferenceUtils.putInt(MyApplication.mContext,"age",ageInt); 
          PreferenceUtils.putFloat(MyApplication.mContext,"weight",weightFloat); 
        }catch (Exception e){ 
          e.printStackTrace(); 
        } 
        new ToastDialog(this).setDuration(2000).setText("保存成功").setAlignment(LayoutAlignment.CENTER).show(); 
        break; 
      case ResourceTable.Id_bt_query: 
         name=PreferenceUtils.getString(MyApplication.mContext,"name"); 
         isMan=PreferenceUtils.getBoolean(MyApplication.mContext,"gender"); 
         age=PreferenceUtils.getInt(MyApplication.mContext,"age"); 
         weight=PreferenceUtils.getFloat(MyApplication.mContext,"weight"); 
        if(isMan){ 
          tvResultQuery.setText("查询结果："+name+"/男/"+age+"/"+weight); 
        }else { 
          tvResultQuery.setText("查询结果："+name+"/女/"+age+"/"+weight); 
        } 
        new ToastDialog(this).setDuration(2000).setText("查询成功").setAlignment(LayoutAlignment.CENTER).show(); 
        break; 
      case ResourceTable.Id_bt_regist: 
        PreferenceUtils.registerObserver(this,new PreferencesObserver() { 
          @Override 
          public void onChange(Preferences preferences, String key) { 
            switch (key){ 
              case "name": 
                 name=PreferenceUtils.getString(MyApplication.mContext,"name"); 
                break; 
              case "gender": 
                 isMan=PreferenceUtils.getBoolean(MyApplication.mContext,"gender"); 
                break; 
              case "age": 
                 age=PreferenceUtils.getInt(MyApplication.mContext,"age"); 
                break; 
              case "weight": 
                 weight=PreferenceUtils.getFloat(MyApplication.mContext,"weight"); 
                break; 
            } 
            if(isMan){ 
              tvResultListener.setText("兼停结果："+name+"/男/"+age+"/"+weight); 
            }else { 
              tvResultListener.setText("兼停结果："+name+"/女/"+age+"/"+weight); 
            } 
          } 
 
        }); 
        new ToastDialog(this).setDuration(2000).setText("注册成功").setAlignment(LayoutAlignment.CENTER).show(); 
        break; 
      case ResourceTable.Id_bt_unregist: 
        PreferenceUtils.unregisterObserver(); 
        new ToastDialog(this).setDuration(2000).setText("解除注册成功").setAlignment(LayoutAlignment.CENTER).show(); 
        break; 
    } 
 
  } 
 
 
 
}

3. MyApplication

public class MyApplication extends AbilityPackage { 
  public static Context mContext ; 
 
  @Override 
  public void onInitialize() { 
    super.onInitialize(); 
    mContext=this; 
  } 
}

4.页面布局ability_main.xml文件

<?xml version="1.0" encoding="utf-8"?> 
<DirectionalLayout 
  xmlns:ohos="http://schemas.huawei.com/res/ohos" 
  ohos:height="match_parent" 
  ohos:orientation="vertical" 
  ohos:width="match_parent"> 
 
  <DirectionalLayout 
    ohos:height="match_content" 
    ohos:width="match_parent" 
    ohos:orientation="vertical" 
    ohos:left_padding="15vp" 
    ohos:right_padding="15vp" 
    ohos:top_padding="16vp"> 
    <Text 
      ohos:height="match_content" 
      ohos:width="match_content" 
      ohos:text="姓名" 
      ohos:text_size="18vp"/> 
    <TextField 
      ohos:id="$+id:tf_name" 
      ohos:height="match_content" 
      ohos:width="match_parent" 
      ohos:text_input_type="pattern_text" 
      ohos:hint="请输入姓名" 
      ohos:text_size="18vp" 
      ohos:hint_color="#cccccc" 
      ohos:top_margin="8vp"/> 
    <DirectionalLayout 
      ohos:height="1vp" 
      ohos:width="match_parent" 
      ohos:top_margin="3vp" 
      ohos:background_element="#cccccc"/> 
  </DirectionalLayout> 
 
 
  <DirectionalLayout 
    ohos:height="match_content" 
    ohos:width="match_parent" 
    ohos:orientation="vertical" 
    ohos:left_padding="15vp" 
    ohos:right_padding="15vp" 
    ohos:top_padding="16vp"> 
    <Text 
      ohos:height="match_content" 
      ohos:width="match_content" 
      ohos:text="性别" 
      ohos:text_size="18vp"/> 
    <TextField 
      ohos:id="$+id:tf_isMan" 
      ohos:height="match_content" 
      ohos:width="match_parent" 
      ohos:text_input_type="pattern_text" 
      ohos:hint="男/女" 
      ohos:text_size="18vp" 
      ohos:hint_color="#cccccc" 
      ohos:top_margin="8vp"/> 
    <DirectionalLayout 
      ohos:height="1vp" 
      ohos:width="match_parent" 
      ohos:top_margin="3vp" 
      ohos:background_element="#cccccc"/> 
  </DirectionalLayout> 
 
 
  <DirectionalLayout 
    ohos:height="match_content" 
    ohos:width="match_parent" 
    ohos:orientation="vertical" 
    ohos:left_padding="15vp" 
    ohos:right_padding="15vp" 
    ohos:top_padding="16vp"> 
    <Text 
      ohos:height="match_content" 
      ohos:width="match_content" 
      ohos:text="年龄" 
      ohos:text_size="18vp"/> 
    <TextField 
      ohos:id="$+id:tf_age" 
      ohos:height="match_content" 
      ohos:width="match_parent" 
      ohos:text_input_type="pattern_number" 
      ohos:hint="请输入年龄" 
      ohos:text_size="18vp" 
      ohos:hint_color="#cccccc" 
      ohos:top_margin="8vp"/> 
    <DirectionalLayout 
      ohos:height="1vp" 
      ohos:width="match_parent" 
      ohos:top_margin="3vp" 
      ohos:background_element="#cccccc"/> 
  </DirectionalLayout> 
 
 
  <DirectionalLayout 
    ohos:height="match_content" 
    ohos:width="match_parent" 
    ohos:orientation="vertical" 
    ohos:left_padding="15vp" 
    ohos:right_padding="15vp" 
    ohos:top_padding="16vp"> 
    <Text 
      ohos:height="match_content" 
      ohos:width="match_content" 
      ohos:text="体重" 
      ohos:text_size="18vp"/> 
    <TextField 
      ohos:id="$+id:tf_weight" 
      ohos:height="match_content" 
      ohos:width="match_parent" 
      ohos:text_input_type="pattern_number" 
      ohos:hint="请输入体重" 
      ohos:text_size="18vp" 
      ohos:hint_color="#cccccc" 
      ohos:top_margin="8vp"/> 
    <DirectionalLayout 
      ohos:height="1vp" 
      ohos:width="match_parent" 
      ohos:top_margin="3vp" 
      ohos:background_element="#cccccc"/> 
  </DirectionalLayout> 
 
 
 
  <DirectionalLayout 
    ohos:height="match_content" 
    ohos:width="match_parent" 
    ohos:orientation="horizontal" 
    ohos:top_margin="30vp" 
    ohos:left_margin="15vp" 
    ohos:right_margin="15vp"> 
    <Button 
      ohos:id="$+id:bt_save" 
      ohos:height="40vp" 
      ohos:width="0" 
      ohos:weight="1" 
      ohos:text="保存" 
      ohos:text_size="20vp" 
      ohos:text_color="#ffffff" 
      ohos:right_margin="30vp" 
      ohos:background_element="$graphic:background_main_circle" 
      ohos:layout_alignment="center"/> 
    <Button 
      ohos:id="$+id:bt_query" 
      ohos:height="40vp" 
      ohos:width="0" 
      ohos:weight="1" 
      ohos:text="查询" 
      ohos:text_size="20vp" 
      ohos:text_color="#ffffff" 
      ohos:right_margin="30vp" 
      ohos:background_element="$graphic:background_main_circle" 
      ohos:layout_alignment="center"/> 
  </DirectionalLayout> 
 
  <DirectionalLayout 
    ohos:height="match_content" 
    ohos:width="match_parent" 
    ohos:orientation="horizontal" 
    ohos:top_margin="30vp" 
    ohos:left_margin="15vp" 
    ohos:right_margin="15vp"> 
    <Button 
      ohos:id="$+id:bt_regist" 
      ohos:height="40vp" 
      ohos:width="0" 
      ohos:weight="1" 
      ohos:text="注册兼停" 
      ohos:text_size="20vp" 
      ohos:text_color="#ffffff" 
      ohos:right_margin="30vp" 
      ohos:background_element="$graphic:background_main_circle" 
      ohos:layout_alignment="center"/> 
    <Button 
      ohos:id="$+id:bt_unregist" 
      ohos:height="40vp" 
      ohos:width="0" 
      ohos:weight="1" 
      ohos:text="解除注册" 
      ohos:text_size="20vp" 
      ohos:text_color="#ffffff" 
      ohos:right_margin="30vp" 
      ohos:background_element="$graphic:background_main_circle" 
      ohos:layout_alignment="center"/> 
  </DirectionalLayout> 
 
 
 
  <Text 
    ohos:id="$+id:tvResultQuery" 
    ohos:height="match_content" 
    ohos:width="match_content" 
    ohos:text_size="18vp" 
    ohos:text="查询结果：" 
    ohos:background_element="#cccccc" 
    ohos:layout_alignment="center" 
    ohos:top_margin="30vp" 
    ohos:padding="10vp"/> 
 
  <Text 
    ohos:id="$+id:tvResultListener" 
    ohos:height="match_content" 
    ohos:width="match_content" 
    ohos:text_size="18vp" 
    ohos:text="兼停结果：" 
    ohos:background_element="#cccccc" 
    ohos:layout_alignment="center" 
    ohos:top_margin="30vp" 
    ohos:padding="10vp"/> 
 
</DirectionalLayout>

5.圆角背景图形background_main_circle.xml文件

<?xml version="1.0" encoding="UTF-8" ?> 
<shape xmlns:ohos="http://schemas.huawei.com/res/ohos" 
       ohos:shape="rectangle"> 
    <corners 
        ohos:radius="10"/> 
    <solid 
        ohos:color="#00aaf5"/> 
 
</shape>