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
从SharedPreference中保存和检索ArrayList
public static void addToPreference(String id,Context context) {
SharedPreferences sharedPreferences = context.getSharedPreferences(Constants.MyPreference, Context.MODE_PRIVATE);
ArrayList<String> list = getListFromPreference(context);
if (!list.contains(id)) {
list.add(id);
SharedPreferences.Editor edit = sharedPreferences.edit();
Set<String> set = new HashSet<>();
set.addAll(list);
edit.putStringSet(Constant.LIST, set);
edit.commit();
}
}
public static ArrayList<String> getListFromPreference(Context context) {
SharedPreferences sharedPreferences = context.getSharedPreferences(Constants.MyPreference, Context.MODE_PRIVATE);
Set<String> set = sharedPreferences.getStringSet(Constant.LIST, null);
ArrayList<String> list = new ArrayList<>();
if (set != null) {
list = new ArrayList<>(set);
}
return list;
}
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);
}
}
我的utils类保存列表到SharedPreferences
public class SharedPrefApi {
private SharedPreferences sharedPreferences;
private Gson gson;
public SharedPrefApi(Context context, Gson gson) {
this.sharedPreferences = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
this.gson = gson;
}
...
public <T> void putList(String key, List<T> list) {
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(key, gson.toJson(list));
editor.apply();
}
public <T> List<T> getList(String key, Class<T> clazz) {
Type typeOfT = TypeToken.getParameterized(List.class, clazz).getType();
return gson.fromJson(getString(key, null), typeOfT);
}
}
使用
// for save
sharedPrefApi.putList(SharedPrefApi.Key.USER_LIST, userList);
// for retrieve
List<User> userList = sharedPrefApi.getList(SharedPrefApi.Key.USER_LIST, User.class);
． 我的utils的完整代码//检查使用实例的活动代码
对于String, int, boolean，最好的选择是sharedPreferences。
如果你想存储数组列表或任何复杂的数据。最好的选择是Paper library。
添加依赖关系
implementation 'io.paperdb:paperdb:2.6'
初始化文件
应该在Application.onCreate()中初始化一次:
Paper.init(context);
Save
List<Person> contacts = ...
Paper.book().write("contacts", contacts);
加载数据
如果对象在存储中不存在，请使用默认值。
List<Person> contacts = Paper.book().read("contacts", new ArrayList<>());
给你。
https://github.com/pilgr/Paper
我已经阅读了上面所有的答案。这都是正确的，但我找到了一个更简单的解决方案如下:
Saving String List in shared-preference>> public static void setSharedPreferenceStringList(Context pContext, String pKey, List<String> pData) { SharedPreferences.Editor editor = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).edit(); editor.putInt(pKey + "size", pData.size()); editor.commit(); for (int i = 0; i < pData.size(); i++) { SharedPreferences.Editor editor1 = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).edit(); editor1.putString(pKey + i, (pData.get(i))); editor1.commit(); } } and for getting String List from Shared-preference>> public static List<String> getSharedPreferenceStringList(Context pContext, String pKey) { int size = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).getInt(pKey + "size", 0); List<String> list = new ArrayList<>(); for (int i = 0; i < size; i++) { list.add(pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).getString(pKey + i, "")); } return list; }
这里的常数。APP_PREFS是要打开的文件的名称;不能包含路径分隔符。
Android sharedpreferences允许您将基本类型(Boolean, Float, Int, Long, String和StringSet，自API11以来可用)作为xml文件保存在内存中。
任何解决方案的关键思想都是将数据转换为这些基本类型之一。
我个人喜欢将my list转换为json格式，然后将其保存为SharedPreferences值中的字符串。
为了使用我的解决方案，你必须添加谷歌gsonlib。
在gradle中只需添加以下依赖项(请使用谷歌的最新版本):
compile 'com.google.code.gson:gson:2.6.2'
保存数据(HttpParam是你的对象):
List<HttpParam> httpParamList = "**get your list**"
String httpParamJSONList = new Gson().toJson(httpParamList);
SharedPreferences prefs = getSharedPreferences(**"your_prefes_key"**, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putString(**"your_prefes_key"**, httpParamJSONList);
editor.apply();
检索数据(HttpParam是你的对象):
SharedPreferences prefs = getSharedPreferences(**"your_prefes_key"**, Context.MODE_PRIVATE);
String httpParamJSONList = prefs.getString(**"your_prefes_key"**, "");
List<HttpParam> httpParamList =
new Gson().fromJson(httpParamJSONList, new TypeToken<List<HttpParam>>() {
}.getType());
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