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
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)
}
其他回答
在API 11之后,SharedPreferences Editor接受set。您可以将List转换为HashSet或类似的东西,并像这样存储它。当你把它读回来时,把它转换成一个数组列表,如果需要的话对它排序,你就可以开始了。
//Retrieve the values
Set<String> set = myScores.getStringSet("key", null);
//Set the values
Set<String> set = new HashSet<String>();
set.addAll(listOfExistingScores);
scoreEditor.putStringSet("key", set);
scoreEditor.commit();
你也可以序列化你的数组列表,然后将它保存/读取到SharedPreferences。解决方案如下:
编辑: 下面是将ArrayList作为一个序列化对象保存到SharedPreferences的解决方案,然后从SharedPreferences中读取它。
因为API只支持在SharedPreferences中存储和检索字符串(在API 11之后,它更简单),我们必须序列化和反序列化ArrayList对象,它将任务列表变成一个字符串。
在TaskManagerApplication类的addTask()方法中,我们必须获取共享首选项的实例,然后使用putString()方法存储序列化的ArrayList:
public void addTask(Task t) {
if (null == currentTasks) {
currentTasks = new ArrayList<task>();
}
currentTasks.add(t);
// save the task list to preference
SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
Editor editor = prefs.edit();
try {
editor.putString(TASKS, ObjectSerializer.serialize(currentTasks));
} catch (IOException e) {
e.printStackTrace();
}
editor.commit();
}
类似地,我们必须从onCreate()方法中的首选项中检索任务列表:
public void onCreate() {
super.onCreate();
if (null == currentTasks) {
currentTasks = new ArrayList<task>();
}
// load tasks from preference
SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
try {
currentTasks = (ArrayList<task>) ObjectSerializer.deserialize(prefs.getString(TASKS, ObjectSerializer.serialize(new ArrayList<task>())));
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
您可以从Apache Pig项目ObjectSerializer.java中获得ObjectSerializer类
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();
在SharedPreferences中保存数组:
public static boolean saveArray()
{
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor mEdit1 = sp.edit();
/* sKey is an array */
mEdit1.putInt("Status_size", sKey.size());
for(int i=0;i<sKey.size();i++)
{
mEdit1.remove("Status_" + i);
mEdit1.putString("Status_" + i, sKey.get(i));
}
return mEdit1.commit();
}
从SharedPreferences加载数组数据
public static void loadArray(Context mContext)
{
SharedPreferences mSharedPreference1 = PreferenceManager.getDefaultSharedPreferences(mContext);
sKey.clear();
int size = mSharedPreference1.getInt("Status_size", 0);
for(int i=0;i<size;i++)
{
sKey.add(mSharedPreference1.getString("Status_" + i, null));
}
}
这应该可以工作:
public void setSections (Context c, List<Section> sectionList){
this.sectionList = sectionList;
Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
String sectionListString = new Gson().toJson(sectionList,sectionListType);
SharedPreferences.Editor editor = getSharedPreferences(c).edit().putString(PREFS_KEY_SECTIONS, sectionListString);
editor.apply();
}
他们,要抓住它才:
public List<Section> getSections(Context c){
if(this.sectionList == null){
String sSections = getSharedPreferences(c).getString(PREFS_KEY_SECTIONS, null);
if(sSections == null){
return new ArrayList<>();
}
Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
try {
this.sectionList = new Gson().fromJson(sSections, sectionListType);
if(this.sectionList == null){
return new ArrayList<>();
}
}catch (JsonSyntaxException ex){
return new ArrayList<>();
}catch (JsonParseException exc){
return new ArrayList<>();
}
}
return this.sectionList;
}
这对我很管用。
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。
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