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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