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
//Set the values
intent.putParcelableArrayListExtra("key",collection);
//Retrieve the values
ArrayList<OnlineMember> onlineMembers = data.getParcelableArrayListExtra("key");
其他回答
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));
}
}
为什么不把数组列表放在应用程序类上呢?它只有在应用被杀死时才会被销毁,所以,只要应用可用,它就会一直存在。
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
这就是你的完美解决方案。试一试,
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(); // This line is IMPORTANT !!!
}
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);
}
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() })
}
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