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
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();
其他回答
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;
}
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。
您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。
使用Kotlin和GSON:
fun <T> SharedPreferences.writeList(gson: Gson, key: String, data: List<T>) {
val json = gson.toJson(data)
edit { putString(key, json) }
}
inline fun <reified T> SharedPreferences.readList(gson: Gson, key: String): List<T> {
val json = getString(key, "[]") ?: "[]"
val type = object : TypeToken<List<T>>() {}.type
return try {
gson.fromJson(json, type)
} catch(e: JsonSyntaxException) {
emptyList()
}
}
你可以使用Gson库保存字符串和自定义数组列表。
首先你需要创建一个函数来保存数组列表到SharedPreferences。
public void saveListInLocal(ArrayList<String> list, String key) {
SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
Gson gson = new Gson();
String json = gson.toJson(list);
editor.putString(key, json);
editor.apply(); // This line is IMPORTANT !!!
}
你需要创建一个函数来从SharedPreferences获取数组列表。
public ArrayList<String> getListFromLocal(String key)
{
SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
Gson gson = new Gson();
String json = prefs.getString(key, null);
Type type = new TypeToken<ArrayList<String>>() {}.getType();
return gson.fromJson(json, type);
}
如何调用保存和检索数组列表函数。
ArrayList<String> listSave=new ArrayList<>();
listSave.add("test1"));
listSave.add("test2"));
saveListInLocal(listSave,"key");
Log.e("saveArrayList:","Save ArrayList success");
ArrayList<String> listGet=new ArrayList<>();
listGet=getListFromLocal("key");
Log.e("getArrayList:","Get ArrayList size"+listGet.size());
不要忘记在你的应用级别build.gradle中添加gson库。
实现“com.google.code.gson: gson: 2.8.2”
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