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
最好的方法是使用GSON转换为JSOn字符串并保存此字符串到SharedPreference。 我还使用这种方式缓存响应。
其他回答
还有Kotlin:
fun SharedPreferences.Editor.putIntegerArrayList(key: String, list: ArrayList<Int>?): SharedPreferences.Editor {
putString(key, list?.joinToString(",") ?: "")
return this
}
fun SharedPreferences.getIntegerArrayList(key: String, defValue: ArrayList<Int>?): ArrayList<Int>? {
val value = getString(key, null)
if (value.isNullOrBlank())
return defValue
return ArrayList (value.split(",").map { it.toInt() })
}
您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。
在SharedPreferences中使用getStringSet和putStringSet非常简单,但在我的情况下,我必须在向Set中添加任何东西之前复制Set对象。否则,Set将不会被保存,如果我的应用程序是强制关闭。可能是因为下面API中的注释。(如果应用程序被返回按钮关闭,则保存)。
注意,您不能修改此调用返回的set实例。如果这样做,则无法保证存储数据的一致性,也无法保证修改实例的能力。 http://developer.android.com/reference/android/content/SharedPreferences.html#getStringSet
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());
SharedPreferences.Editor editor = prefs.edit();
Set<String> outSet = prefs.getStringSet("key", new HashSet<String>());
Set<String> workingSet = new HashSet<String>(outSet);
workingSet.add("Another String");
editor.putStringSet("key", workingSet);
editor.commit();
您可以使用序列化或Gson库将列表转换为字符串,反之亦然,然后将字符串保存在首选项中。
使用谷歌的Gson库:
//Converting list to string
new Gson().toJson(list);
//Converting string to list
new Gson().fromJson(listString, CustomObjectsList.class);
使用Java序列化:
//Converting list to string
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(list);
oos.flush();
String string = Base64.encodeToString(bos.toByteArray(), Base64.DEFAULT);
oos.close();
bos.close();
return string;
//Converting string to list
byte[] bytesArray = Base64.decode(familiarVisitsString, Base64.DEFAULT);
ByteArrayInputStream bis = new ByteArrayInputStream(bytesArray);
ObjectInputStream ois = new ObjectInputStream(bis);
Object clone = ois.readObject();
ois.close();
bis.close();
return (CustomObjectsList) clone;
该方法用于存储/保存数组列表:-
public static void saveSharedPreferencesLogList(Context context, List<String> collageList) {
SharedPreferences mPrefs = context.getSharedPreferences("PhotoCollage", context.MODE_PRIVATE);
SharedPreferences.Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(collageList);
prefsEditor.putString("myJson", json);
prefsEditor.commit();
}
该方法用于检索数组列表:-
public static List<String> loadSharedPreferencesLogList(Context context) {
List<String> savedCollage = new ArrayList<String>();
SharedPreferences mPrefs = context.getSharedPreferences("PhotoCollage", context.MODE_PRIVATE);
Gson gson = new Gson();
String json = mPrefs.getString("myJson", "");
if (json.isEmpty()) {
savedCollage = new ArrayList<String>();
} else {
Type type = new TypeToken<List<String>>() {
}.getType();
savedCollage = gson.fromJson(json, type);
}
return savedCollage;
}
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