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

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()
    }
}

其他回答

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();

从SharedPreference中保存和检索ArrayList

 public static void addToPreference(String id,Context context) {
        SharedPreferences sharedPreferences = context.getSharedPreferences(Constants.MyPreference, Context.MODE_PRIVATE);
        ArrayList<String> list = getListFromPreference(context);
        if (!list.contains(id)) {
            list.add(id);
            SharedPreferences.Editor edit = sharedPreferences.edit();
            Set<String> set = new HashSet<>();
            set.addAll(list);
            edit.putStringSet(Constant.LIST, set);
            edit.commit();

        }
    }
    public static ArrayList<String> getListFromPreference(Context context) {
        SharedPreferences sharedPreferences = context.getSharedPreferences(Constants.MyPreference, Context.MODE_PRIVATE);
        Set<String> set = sharedPreferences.getStringSet(Constant.LIST, null);
        ArrayList<String> list = new ArrayList<>();
        if (set != null) {
            list = new ArrayList<>(set);
        }
        return list;
    }

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)
}  

以防有人需要保存列表的列表,即list < list < String > >。我是这样做的:

序列化

Gson gson = new Gson();
// Save the size of the array
sharedPreferencesEditor.putInt("ArraySize", myArray.size());

for (int i=0; i<myArray.size(); i++) {
  String key = "Array"+i;
  String json = gson.toJson(myArray.get(i));
  sharedPreferencesEditor.putString(key, json);
}

sharedPreferencesEditor.commit();

反序列化

// Get the size of the array to be deserialized. In my case, the default number should be 3
int arraySize = sharedPreferences.getInt("ArraySize",3);

myArray = new ArrayList<List<String>>();

for (int i=0; i<arraySize; i++) {
  String key = "Array"+i;
  String json = sharedPreferences.getString(key, null);
  List<String> arrayTemp= gson.fromJson(json, List.class);
  myArray.add(arrayTemp);
}

// My array may also include components with empty strings. 
// Gson makes them null values and it is not possible 
// to deserialize them as empty strings. 
// The following takes care of that:

for (int i=0; i<myArray.size();i++) {
   if (myArray.get(i) == null) {
      List<String> emptyComponent = new ArrayList<String>() {
         { add(""); }
      };
      myArray.set(i,emptyComponent);
   }
}

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());
    }
}