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
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));
其他回答
以上答案都是正确的。:)我自己就用了其中一个。然而，当我读到这个问题时，我发现这篇文章实际上是在谈论一个不同的场景，如果我没有弄错的话。
"我需要这个数组一直存在即使用户离开了活动然后想要在稍后的时间回来"
实际上，他希望数据一直存储到应用程序打开为止，而不管用户在应用程序中更换屏幕。
“然而，我不需要阵列可用后，应用程序已完全关闭”
但是一旦应用程序关闭，数据就不应该被保存。因此，我觉得使用SharedPreferences并不是最优的方式。
对于这个需求，我们可以创建一个扩展Application类的类。
public class MyApp extends Application {
//Pardon me for using global ;)
private ArrayList<CustomObject> globalArray;
public void setGlobalArrayOfCustomObjects(ArrayList<CustomObject> newArray){
globalArray = newArray;
}
public ArrayList<CustomObject> getGlobalArrayOfCustomObjects(){
return globalArray;
}
}
通过setter和getter，可以从应用程序中的任何地方访问ArrayList。最好的部分是一旦应用程序关闭，我们不必担心数据被存储。：）
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
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)
}
public class VcareSharedPreference {
private static VcareSharedPreference sharePref = new VcareSharedPreference();
private static SharedPreferences sharedPreferences;
private static SharedPreferences.Editor editor;
private VcareSharedPreference() {
}
public static VcareSharedPreference getInstance(Context context) {
if (sharedPreferences == null) {
sharedPreferences = context.getSharedPreferences(context.getPackageName(), Activity.MODE_PRIVATE);
editor = sharedPreferences.edit();
}
return sharePref;
}
public void save(String KEY, String text) {
editor.putString(KEY, text);
editor.commit();
}
public String getValue(String PREFKEY) {
String text;
//settings = PreferenceManager.getDefaultSharedPreferences(context);
text = sharedPreferences.getString(PREFKEY, null);
return text;
}
public void removeValue(String KEY) {
editor.remove(KEY);
editor.commit();
}
public void clearAll() {
editor.clear();
editor.commit();
}
public void saveArrayList(String key, ArrayList<ModelWelcome> modelCourses) {
Gson gson = new Gson();
String json = gson.toJson(modelCourses);
editor.putString(key, json);
editor.apply();
}
public ArrayList<ModelWelcome> getArray(String key) {
Gson gson = new Gson();
String json = sharedPreferences.getString(key, null);
Type type = new TypeToken<ArrayList<ModelWelcome>>() {
}.getType();
return gson.fromJson(json, type);}}
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);
}
}
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