Android(安卓)SharedPreferences存储的正确写法

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。那么该如何处理好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，创建方法只有通过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。

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);

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