I have an ArrayList with custom objects. Each custom object contains a variety of strings and numbers. I need the array to stick around even if the user leaves the activity and then wants to come back at a later time, however I don't need the array available after the application has been closed completely. I save a lot of other objects this way by using the SharedPreferences but I can't figure out how to save my entire array this way. Is this possible? Maybe SharedPreferences isn't the way to go about this? Is there a simpler method?


当前回答

这应该可以工作:

public void setSections (Context c,  List<Section> sectionList){
    this.sectionList = sectionList;

    Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
    String sectionListString = new Gson().toJson(sectionList,sectionListType);

    SharedPreferences.Editor editor = getSharedPreferences(c).edit().putString(PREFS_KEY_SECTIONS, sectionListString);
    editor.apply();
}

他们,要抓住它才:

public List<Section> getSections(Context c){

    if(this.sectionList == null){
        String sSections = getSharedPreferences(c).getString(PREFS_KEY_SECTIONS, null);

        if(sSections == null){
            return new ArrayList<>();
        }

        Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
        try {

            this.sectionList = new Gson().fromJson(sSections, sectionListType);

            if(this.sectionList == null){
                return new ArrayList<>();
            }
        }catch (JsonSyntaxException ex){

            return new ArrayList<>();

        }catch (JsonParseException exc){

            return new ArrayList<>();
        }
    }
    return this.sectionList;
}

这对我很管用。

其他回答

你可以从FacebookSDK的SharedPreferencesTokenCache类中引用serializeKey()和deserializeKey()函数。它将supportedType转换为JSON对象,并将JSON字符串存储为SharedPreferences。你可以从这里下载SDK

private void serializeKey(String key, Bundle bundle, SharedPreferences.Editor editor)
    throws JSONException {
    Object value = bundle.get(key);
    if (value == null) {
        // Cannot serialize null values.
        return;
    }

    String supportedType = null;
    JSONArray jsonArray = null;
    JSONObject json = new JSONObject();

    if (value instanceof Byte) {
        supportedType = TYPE_BYTE;
        json.put(JSON_VALUE, ((Byte)value).intValue());
    } else if (value instanceof Short) {
        supportedType = TYPE_SHORT;
        json.put(JSON_VALUE, ((Short)value).intValue());
    } else if (value instanceof Integer) {
        supportedType = TYPE_INTEGER;
        json.put(JSON_VALUE, ((Integer)value).intValue());
    } else if (value instanceof Long) {
        supportedType = TYPE_LONG;
        json.put(JSON_VALUE, ((Long)value).longValue());
    } else if (value instanceof Float) {
        supportedType = TYPE_FLOAT;
        json.put(JSON_VALUE, ((Float)value).doubleValue());
    } else if (value instanceof Double) {
        supportedType = TYPE_DOUBLE;
        json.put(JSON_VALUE, ((Double)value).doubleValue());
    } else if (value instanceof Boolean) {
        supportedType = TYPE_BOOLEAN;
        json.put(JSON_VALUE, ((Boolean)value).booleanValue());
    } else if (value instanceof Character) {
        supportedType = TYPE_CHAR;
        json.put(JSON_VALUE, value.toString());
    } else if (value instanceof String) {
        supportedType = TYPE_STRING;
        json.put(JSON_VALUE, (String)value);
    } else {
        // Optimistically create a JSONArray. If not an array type, we can null
        // it out later
        jsonArray = new JSONArray();
        if (value instanceof byte[]) {
            supportedType = TYPE_BYTE_ARRAY;
            for (byte v : (byte[])value) {
                jsonArray.put((int)v);
            }
        } else if (value instanceof short[]) {
            supportedType = TYPE_SHORT_ARRAY;
            for (short v : (short[])value) {
                jsonArray.put((int)v);
            }
        } else if (value instanceof int[]) {
            supportedType = TYPE_INTEGER_ARRAY;
            for (int v : (int[])value) {
                jsonArray.put(v);
            }
        } else if (value instanceof long[]) {
            supportedType = TYPE_LONG_ARRAY;
            for (long v : (long[])value) {
                jsonArray.put(v);
            }
        } else if (value instanceof float[]) {
            supportedType = TYPE_FLOAT_ARRAY;
            for (float v : (float[])value) {
                jsonArray.put((double)v);
            }
        } else if (value instanceof double[]) {
            supportedType = TYPE_DOUBLE_ARRAY;
            for (double v : (double[])value) {
                jsonArray.put(v);
            }
        } else if (value instanceof boolean[]) {
            supportedType = TYPE_BOOLEAN_ARRAY;
            for (boolean v : (boolean[])value) {
                jsonArray.put(v);
            }
        } else if (value instanceof char[]) {
            supportedType = TYPE_CHAR_ARRAY;
            for (char v : (char[])value) {
                jsonArray.put(String.valueOf(v));
            }
        } else if (value instanceof List<?>) {
            supportedType = TYPE_STRING_LIST;
            @SuppressWarnings("unchecked")
            List<String> stringList = (List<String>)value;
            for (String v : stringList) {
                jsonArray.put((v == null) ? JSONObject.NULL : v);
            }
        } else {
            // Unsupported type. Clear out the array as a precaution even though
            // it is redundant with the null supportedType.
            jsonArray = null;
        }
    }

    if (supportedType != null) {
        json.put(JSON_VALUE_TYPE, supportedType);
        if (jsonArray != null) {
            // If we have an array, it has already been converted to JSON. So use
            // that instead.
            json.putOpt(JSON_VALUE, jsonArray);
        }

        String jsonString = json.toString();
        editor.putString(key, jsonString);
    }
}

private void deserializeKey(String key, Bundle bundle)
        throws JSONException {
    String jsonString = cache.getString(key, "{}");
    JSONObject json = new JSONObject(jsonString);

    String valueType = json.getString(JSON_VALUE_TYPE);

    if (valueType.equals(TYPE_BOOLEAN)) {
        bundle.putBoolean(key, json.getBoolean(JSON_VALUE));
    } else if (valueType.equals(TYPE_BOOLEAN_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        boolean[] array = new boolean[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = jsonArray.getBoolean(i);
        }
        bundle.putBooleanArray(key, array);
    } else if (valueType.equals(TYPE_BYTE)) {
        bundle.putByte(key, (byte)json.getInt(JSON_VALUE));
    } else if (valueType.equals(TYPE_BYTE_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        byte[] array = new byte[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = (byte)jsonArray.getInt(i);
        }
        bundle.putByteArray(key, array);
    } else if (valueType.equals(TYPE_SHORT)) {
        bundle.putShort(key, (short)json.getInt(JSON_VALUE));
    } else if (valueType.equals(TYPE_SHORT_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        short[] array = new short[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = (short)jsonArray.getInt(i);
        }
        bundle.putShortArray(key, array);
    } else if (valueType.equals(TYPE_INTEGER)) {
        bundle.putInt(key, json.getInt(JSON_VALUE));
    } else if (valueType.equals(TYPE_INTEGER_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        int[] array = new int[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = jsonArray.getInt(i);
        }
        bundle.putIntArray(key, array);
    } else if (valueType.equals(TYPE_LONG)) {
        bundle.putLong(key, json.getLong(JSON_VALUE));
    } else if (valueType.equals(TYPE_LONG_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        long[] array = new long[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = jsonArray.getLong(i);
        }
        bundle.putLongArray(key, array);
    } else if (valueType.equals(TYPE_FLOAT)) {
        bundle.putFloat(key, (float)json.getDouble(JSON_VALUE));
    } else if (valueType.equals(TYPE_FLOAT_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        float[] array = new float[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = (float)jsonArray.getDouble(i);
        }
        bundle.putFloatArray(key, array);
    } else if (valueType.equals(TYPE_DOUBLE)) {
        bundle.putDouble(key, json.getDouble(JSON_VALUE));
    } else if (valueType.equals(TYPE_DOUBLE_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        double[] array = new double[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            array[i] = jsonArray.getDouble(i);
        }
        bundle.putDoubleArray(key, array);
    } else if (valueType.equals(TYPE_CHAR)) {
        String charString = json.getString(JSON_VALUE);
        if (charString != null && charString.length() == 1) {
            bundle.putChar(key, charString.charAt(0));
        }
    } else if (valueType.equals(TYPE_CHAR_ARRAY)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        char[] array = new char[jsonArray.length()];
        for (int i = 0; i < array.length; i++) {
            String charString = jsonArray.getString(i);
            if (charString != null && charString.length() == 1) {
                array[i] = charString.charAt(0);
            }
        }
        bundle.putCharArray(key, array);
    } else if (valueType.equals(TYPE_STRING)) {
        bundle.putString(key, json.getString(JSON_VALUE));
    } else if (valueType.equals(TYPE_STRING_LIST)) {
        JSONArray jsonArray = json.getJSONArray(JSON_VALUE);
        int numStrings = jsonArray.length();
        ArrayList<String> stringList = new ArrayList<String>(numStrings);
        for (int i = 0; i < numStrings; i++) {
            Object jsonStringValue = jsonArray.get(i);
            stringList.add(i, jsonStringValue == JSONObject.NULL ? null : (String)jsonStringValue);
        }
        bundle.putStringArrayList(key, stringList);
    }
}

您还可以将数组列表转换为String并优先保存

private String convertToString(ArrayList<String> list) {

            StringBuilder sb = new StringBuilder();
            String delim = "";
            for (String s : list)
            {
                sb.append(delim);
                sb.append(s);;
                delim = ",";
            }
            return sb.toString();
        }

private ArrayList<String> convertToArray(String string) {

            ArrayList<String> list = new ArrayList<String>(Arrays.asList(string.split(",")));
            return list;
        }

您可以使用convertToString方法将数组列表转换为字符串后保存它,并使用convertToArray方法检索字符串并将其转换为数组

在API 11之后,你可以直接保存设置到SharedPreferences !!:)

请在kotlin中使用这两种方法将数据存储在ArrayList中

fun setDataInArrayList(list: ArrayList<ShopReisterRequest>, key: String, context: Context) {
    val prefs = PreferenceManager.getDefaultSharedPreferences(context)
    val editor = prefs.edit()
    val gson = Gson()
    val json = gson.toJson(list)
    editor.putString(key, json)
    editor.apply()   
}

fun getDataInArrayList(key: String, context: Context): ArrayList<ShopReisterRequest> {
    val prefs = PreferenceManager.getDefaultSharedPreferences(context)
    val gson = Gson()
    val json = prefs.getString(key, null)
    val type = object : TypeToken<ArrayList<ShopReisterRequest>>() {

    }.type
    return gson.fromJson<ArrayList<ShopReisterRequest>>(json, type)
}  

使用这个自定义类:

public class SharedPreferencesUtil {

    public static void pushStringList(SharedPreferences sharedPref, 
                                      List<String> list, String uniqueListName) {

        SharedPreferences.Editor editor = sharedPref.edit();
        editor.putInt(uniqueListName + "_size", list.size());

        for (int i = 0; i < list.size(); i++) {
            editor.remove(uniqueListName + i);
            editor.putString(uniqueListName + i, list.get(i));
        }
        editor.apply();
    }

    public static List<String> pullStringList(SharedPreferences sharedPref, 
                                              String uniqueListName) {

        List<String> result = new ArrayList<>();
        int size = sharedPref.getInt(uniqueListName + "_size", 0);

        for (int i = 0; i < size; i++) {
            result.add(sharedPref.getString(uniqueListName + i, null));
        }
        return result;
    }
}

使用方法:

SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);
SharedPreferencesUtil.pushStringList(sharedPref, list, getString(R.string.list_name));
List<String> list = SharedPreferencesUtil.pullStringList(sharedPref, getString(R.string.list_name));

下面的代码是公认的答案,为新手(我)多写几行,例如。说明了如何将set类型对象转换回arrayList,并提供了关于`之前操作的附加指导。putStringSet'和。getstringset '。(谢谢你邪恶)

// shared preferences
   private SharedPreferences preferences;
   private SharedPreferences.Editor nsuserdefaults;

// setup persistent data
        preferences = this.getSharedPreferences("MyPreferences", MainActivity.MODE_PRIVATE);
        nsuserdefaults = preferences.edit();

        arrayOfMemberUrlsUserIsFollowing = new ArrayList<String>();
        //Retrieve followers from sharedPreferences
        Set<String> set = preferences.getStringSet("following", null);

        if (set == null) {
            // lazy instantiate array
            arrayOfMemberUrlsUserIsFollowing = new ArrayList<String>();
        } else {
            // there is data from previous run
            arrayOfMemberUrlsUserIsFollowing = new ArrayList<>(set);
        }

// convert arraylist to set, and save arrayOfMemberUrlsUserIsFollowing to nsuserdefaults
                Set<String> set = new HashSet<String>();
                set.addAll(arrayOfMemberUrlsUserIsFollowing);
                nsuserdefaults.putStringSet("following", set);
                nsuserdefaults.commit();