为什么我的共享偏好不工作?—检索到的Object为空

Question

我试图保存一个对象的ColorBean类，当应用程序去onStop()

public class MainActivity extends ExpandableListActivity {
    private ColorAdapter expListAdapter;
        LinkedHashMap<String, ArrayList<ColorBean>> colorsMap2 = new LinkedHashMap<String, ArrayList<ColorBean>>();
        SharedPreferences prefs;
        static String fileName = "SharedObject";
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle icicle) {
            super.onCreate(icicle);
            setContentView(R.layout.main);
            ArrayList<String> groupNames = new ArrayList<String>();
            prefs = getPreferences(MODE_PRIVATE);
            final LinkedHashMap<String, ArrayList<ColorBean>> colorsMap = new LinkedHashMap<String, ArrayList<ColorBean>>();
            ArrayList<ColorBean> color = new ArrayList<ColorBean>();
            //Trying to fetch the prefs
            colorsMap2 = (LinkedHashMap<String, ArrayList<ColorBean>>) loadFromSharedPrefs();
            if (colorsMap2 == null || colorsMap2.size() == 0)
                Toast.makeText(this, "Not Retrieved", Toast.LENGTH_SHORT).show();
        }
        @Override
        protected void onResume() {
            super.onResume();
            //fetching them here too
            if (loadFromSharedPrefs() != null) {
                colorsMap2 = (LinkedHashMap<String, ArrayList<ColorBean>>) loadFromSharedPrefs();
            }
        }
        @Override
        protected void onStop() {
            super.onStop();
            //saving the preferences
            saveToSharedPrefs(colorsMap2);
        }
        public void saveToSharedPrefs(Object objToSave) {
            SharedPreferences.Editor editor = prefs.edit();
            Gson gson = new Gson();
            String json = gson.toJson(objToSave);
            editor.putString("MyObject", json);
            editor.commit();
        }
        public Object loadFromSharedPrefs() {
            Toast.makeText(this, "loading", Toast.LENGTH_SHORT).show();
            Gson gson = new Gson();
            Object obj = null;
            if (prefs != null) {
                String json = prefs.getString("MyObject", "");
                obj = gson.fromJson(json, Object.class);
            }
            return obj;
        }
    }

Answer 1

看起来您需要更改行:

obj = gson.fromJson(json, Object.class);

:

obj = gson.fromJson(json, LinkedHashMap<String, ArrayList<ColorBean>>.class);

对不起，我已经有一段时间没有使用Gson了，是的，你是对的，我上面说的不起作用。在序列化类型时需要存储泛型类型信息，因此在序列化和反序列化时需要使用Gson的TypeToken类:

Type mapType = new TypeToken<LinkedHashMap<String, ArrayList<ColorBean>>>(){}.getType();

然后使用:

序列化

String json = gson.toJson(objToSave, mapType);

和反序列化使用:

obj = gson.fromJson(json, mapType);

这里有一个教程，介绍使用通用类型的Gson