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
正如@nirav所说,最好的解决方案是使用Gson实用工具类将其作为json文本存储在sharedpreferences中。下面是示例代码:
//Retrieve the values
Gson gson = new Gson();
String jsonText = Prefs.getString("key", null);
String[] text = gson.fromJson(jsonText, String[].class); //EDIT: gso to gson
//Set the values
Gson gson = new Gson();
List<String> textList = new ArrayList<String>(data);
String jsonText = gson.toJson(textList);
prefsEditor.putString("key", jsonText);
prefsEditor.apply();
其他回答
正如@nirav所说,最好的解决方案是使用Gson实用工具类将其作为json文本存储在sharedpreferences中。下面是示例代码:
//Retrieve the values
Gson gson = new Gson();
String jsonText = Prefs.getString("key", null);
String[] text = gson.fromJson(jsonText, String[].class); //EDIT: gso to gson
//Set the values
Gson gson = new Gson();
List<String> textList = new ArrayList<String>(data);
String jsonText = gson.toJson(textList);
prefsEditor.putString("key", jsonText);
prefsEditor.apply();
您可以将其转换为Map Object来存储它,然后在检索SharedPreferences时将值更改回ArrayList。
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);}}
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);
}
}
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;
}
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