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
正如@nirav所说,最好的解决方案是使用Gson实用工具类将其作为json文本存储在sharedpreferences中。下面是示例代码:
//Retrieve the values
Gson gson = new Gson();
String jsonText = Prefs.getString("key", null);
String[] text = gson.fromJson(jsonText, String[].class); //EDIT: gso to gson
//Set the values
Gson gson = new Gson();
List<String> textList = new ArrayList<String>(data);
String jsonText = gson.toJson(textList);
prefsEditor.putString("key", jsonText);
prefsEditor.apply();
其他回答
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。
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);
}
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”
使用这个自定义类:
public class SharedPreferencesUtil {
public static void pushStringList(SharedPreferences sharedPref,
List<String> list, String uniqueListName) {
SharedPreferences.Editor editor = sharedPref.edit();
editor.putInt(uniqueListName + "_size", list.size());
for (int i = 0; i < list.size(); i++) {
editor.remove(uniqueListName + i);
editor.putString(uniqueListName + i, list.get(i));
}
editor.apply();
}
public static List<String> pullStringList(SharedPreferences sharedPref,
String uniqueListName) {
List<String> result = new ArrayList<>();
int size = sharedPref.getInt(uniqueListName + "_size", 0);
for (int i = 0; i < size; i++) {
result.add(sharedPref.getString(uniqueListName + i, null));
}
return result;
}
}
使用方法:
SharedPreferences sharedPref = getPreferences(Context.MODE_PRIVATE);
SharedPreferencesUtil.pushStringList(sharedPref, list, getString(R.string.list_name));
List<String> list = SharedPreferencesUtil.pullStringList(sharedPref, getString(R.string.list_name));
//Set the values
intent.putParcelableArrayListExtra("key",collection);
//Retrieve the values
ArrayList<OnlineMember> onlineMembers = data.getParcelableArrayListExtra("key");
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