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
我使用相同的方式保存和检索字符串,但这里我使用HashSet作为数组列表的中介
使用HashSet保存arrayList到SharedPreferences:
1-我们创建SharedPreferences变量(在数组发生变化的地方)
2 -我们将数组列表转换为HashSet
3 -然后放入stringSet并应用
4 -你在HashSet中获取stringset并重新创建ArrayList来设置HashSet。
public class MainActivity extends AppCompatActivity {
ArrayList<String> arrayList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SharedPreferences prefs = this.getSharedPreferences("com.example.nec.myapplication", Context.MODE_PRIVATE);
HashSet<String> set = new HashSet(arrayList);
prefs.edit().putStringSet("names", set).apply();
set = (HashSet<String>) prefs.getStringSet("names", null);
arrayList = new ArrayList(set);
Log.i("array list", arrayList.toString());
}
}
其他回答
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);}}
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
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。
您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。
/**
* 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)
}
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