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
以防有人需要保存列表的列表，即list < list < String > >。我是这样做的:
序列化
Gson gson = new Gson();
// Save the size of the array
sharedPreferencesEditor.putInt("ArraySize", myArray.size());
for (int i=0; i<myArray.size(); i++) {
String key = "Array"+i;
String json = gson.toJson(myArray.get(i));
sharedPreferencesEditor.putString(key, json);
}
sharedPreferencesEditor.commit();
反序列化
// Get the size of the array to be deserialized. In my case, the default number should be 3
int arraySize = sharedPreferences.getInt("ArraySize",3);
myArray = new ArrayList<List<String>>();
for (int i=0; i<arraySize; i++) {
String key = "Array"+i;
String json = sharedPreferences.getString(key, null);
List<String> arrayTemp= gson.fromJson(json, List.class);
myArray.add(arrayTemp);
}
// My array may also include components with empty strings.
// Gson makes them null values and it is not possible
// to deserialize them as empty strings.
// The following takes care of that:
for (int i=0; i<myArray.size();i++) {
if (myArray.get(i) == null) {
List<String> emptyComponent = new ArrayList<String>() {
{ add(""); }
};
myArray.set(i,emptyComponent);
}
}
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);
}
}
/**
* Save and get ArrayList in SharedPreference
*/
JAVA:
public void saveArrayList(ArrayList<String> list, String key){
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(activity);
SharedPreferences.Editor editor = prefs.edit();
Gson gson = new Gson();
String json = gson.toJson(list);
editor.putString(key, json);
editor.apply();
}
public ArrayList<String> getArrayList(String key){
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(activity);
Gson gson = new Gson();
String json = prefs.getString(key, null);
Type type = new TypeToken<ArrayList<String>>() {}.getType();
return gson.fromJson(json, type);
}
科特林
fun saveArrayList(list: java.util.ArrayList<String?>?, key: String?) {
val prefs: SharedPreferences = PreferenceManager.getDefaultSharedPreferences(activity)
val editor: Editor = prefs.edit()
val gson = Gson()
val json: String = gson.toJson(list)
editor.putString(key, json)
editor.apply()
}
fun getArrayList(key: String?): java.util.ArrayList<String?>? {
val prefs: SharedPreferences = PreferenceManager.getDefaultSharedPreferences(activity)
val gson = Gson()
val json: String = prefs.getString(key, null)
val type: Type = object : TypeToken<java.util.ArrayList<String?>?>() {}.getType()
return gson.fromJson(json, type)
}
//Set the values
intent.putParcelableArrayListExtra("key",collection);
//Retrieve the values
ArrayList<OnlineMember> onlineMembers = data.getParcelableArrayListExtra("key");
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 !!：）
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();
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