SharedPreferences该怎样写

转载自SharedPreferences该怎样写

SharedPreferences 特点

即便是 Android 小白都知道的 SharedPreferences 的用法，这是保存数据最简便的方法，但是不处理好的话后期维护将是一个巨大的坑。那么该如何处理 SharedPreferences 才方便维护呢。先从它的特点开始入手吧。

● 通过 Context.getSharedPreferences() 获取的 SharedPreferences 是一个单例 SharedPreferences.edit() 每次都会创建一个新的编辑对象， commit() 之前一切改动都无效

● SharedPreferences 的具体实现并不在公开 API 内，创建方法只有通 Context 获取。具体实现我们不去研究，通过 Log 打印每次获取的对象都是同一个，同样的方法可知道每次 edit() 都会得到不同的对象。

难以维护的 SharedPreferences

  SharedPreference userPreferences = context.getSharedPreferences("UserInfo", Context.MODE_PRIVATE);
  userPreferences.edit()
      .putString("id", "myId")
      .putString("name", "myName")
      .putString("head", "myHead")
      .commit();
  Log.e("id", userPreferences.getString("id",""));
  Log.e("name", userPreferences.getString("name",""));
  Log.e("head", userPreferences.getString("head",""));

如上一段 SharedPreferences 保存和读取的方法非常简便，正因此才不易维护，可能因为写错 Key 而找不出问题所在，当然一般我们都会把 Key 写成静态常量。但随着项目增大，可能需要多处修改用户信息，每次都要一个个put() , 除了写着厌烦看着难受，当遇到需要增加或减少字段时也非常不便。

SharedPreferences 该这么写

如果能保留原有写法，又能规范方法那是最好不过了，看下SharedPreferences 的接口方法并不多，很容易就写个包装类封装下。** PreferencesWrapper 是装饰模式，这里作用是替代继承，因为没法直接继承SharedPreferences 的实现类**

  import android.content.SharedPreferences;
  import android.support.annotation.Nullable;

  import java.util.Map;
  import java.util.Set;

  /**
   * SharedPreferences 包装类
   * Created by wittytutu on 17-3-29.
   */

  public class PreferencesWrapper implements SharedPreferences {

    protected SharedPreferences mPreferences;

    public PreferencesWrapper(SharedPreferences preferences) {
         mPreferences = preferences;
    }

    @Override
    public Map getAll() {
        return mPreferences.getAll();
    }

    @Nullable
    @Override
    public String getString(String key, @Nullable String defValue) {
        return mPreferences.getString(key, defValue);
    }

    @Nullable
    @Override
    public Set getStringSet(String key, @Nullable Set defValues) {
        return mPreferences.getStringSet(key, defValues);
    }

    @Override
    public int getInt(String key, int defValue) {
        return mPreferences.getInt(key, defValue);
    }

    @Override
    public long getLong(String key, long defValue) {
        return mPreferences.getLong(key, defValue);
    }

    @Override
    public float getFloat(String key, float defValue) {
        return mPreferences.getFloat(key, defValue);
    }

    @Override
    public boolean getBoolean(String key, boolean defValue) {
        return mPreferences.getBoolean(key, defValue);
    }

    @Override
    public boolean contains(String key) {
        return mPreferences.contains(key);
    }

    @Override
    public EditorWrapper edit() {
        return new EditorWrapper(mPreferences.edit());
    }

    @Override
    public void registerOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener) {
        mPreferences.registerOnSharedPreferenceChangeListener(listener);
    }

     @Override
     public void unregisterOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener) {
      mPreferences.unregisterOnSharedPreferenceChangeListener(listener);
     }

     public static class EditorWrapper implements Editor {
        protected Editor mEditor;

        public EditorWrapper(Editor editor) {
            mEditor = editor;
        }

        @Override
        public EditorWrapper putString(String key, @Nullable String value) {
            mEditor.putString(key, value);
            return this;
        }

        @Override
        public EditorWrapper putStringSet(String key, @Nullable Set values) {
            mEditor.putStringSet(key, values);
            return this;
        }

        @Override
        public EditorWrapper putInt(String key, int value) {
            mEditor.putInt(key, value);
            return this;
         }

        @Override
        public EditorWrapper putLong(String key, long value) {
            mEditor.putLong(key, value);
            return this;
        }

        @Override
        public EditorWrapper putFloat(String key, float value) {
            mEditor.putFloat(key, value);
            return this;
        }

        @Override
        public EditorWrapper putBoolean(String key, boolean value) {
            mEditor.putBoolean(key, value);
            return this;
        }

        @Override
        public EditorWrapper remove(String key) {
            mEditor.remove(key);
            return this;
        }

        @Override
        public EditorWrapper clear() {
            mEditor.clear();
            return this;
        }

        @Override
        public boolean commit() {
            return mEditor.commit();
        }

        @Override
        public void apply() {
            mEditor.apply();
        }
    }
}

接下来的使用就简单了

public class UserInfoPreferences extends PreferencesWrapper {
    private static final String NAME = "UserInfo";

    public static final KEY_ID = "id"
    public static final KEY_NAME = "name";
    public static final KEY_HEAD = "head";
    public static final KEY_SEX = "sex";

    private static volatile UserInfoPreferences mPreferences;

    public static UserInfoPreferences getInstance(Context context){
        if(mPreferences == null) {
            synchronized (UserInfoPreferences.class){
                if(mPreferences == null) {
                    SharedPreferences preferences = context.getApplicationCtontext().getShaedPreferences(NAME, Context.MODE_PRIVATE);
                    mPreferences = new UserInfoPreferences(preferences);
                }
            }
        }
        return mPreferences;
    }

    public UserInfoPreferences(SharedPreferences preferences) {
        super(preferences);
    }

    // 获取用户信息
    public UserInfo getUserInfo(){
        String id = mPreferences.getString(KEY_ID, "");
        String name = mPreferences.getString(KEY_NAME, "");
        String head = mPreferences.getString(KEY_HEAD, "");
        return new UserInfo(id, name, head);
    }

    @Override
    public Editor edit(){
        return new Editor(mPreferences.edit());
    }

    public static class Editor extends EditorWrapper {

        public Editor(SharedPreferences.Editor editor) {
            super(editor);
        }

        // 保存用户信息
        public Editor putUserInfo(String id, String name, String head) {

            mEditor.putString(KEY_ID, id)
                    .putString(KEY_AME, name)
                    .putString(KEY_HEAD, head);
            return this;
        }

        // 清空用户信息
        public Editor clearUserInfo() {

            mEditor.remove(KEY_ID)
                    .remove(KEY_NAME)
                    .remove(KEY_HEAD);
            return this;
        }
    }
}

调用即方便扩展，也保留了原有方法。

UserInfoPreferences preferences = UserInfoPreferences.getInstance(context);
preferences.edit()
    .clearUserInfo()
    .putUserInfo("myId", "myName", "myHead")
    .putInt(KEY_SEX, 0)
    .commit();
UserInfo userInfo = preferences.getUserInfo();
int sex = preferences.getInt(KEY_SEX, 0);