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

这应该可以工作:

public void setSections (Context c,  List<Section> sectionList){
    this.sectionList = sectionList;

    Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
    String sectionListString = new Gson().toJson(sectionList,sectionListType);

    SharedPreferences.Editor editor = getSharedPreferences(c).edit().putString(PREFS_KEY_SECTIONS, sectionListString);
    editor.apply();
}

他们,要抓住它才:

public List<Section> getSections(Context c){

    if(this.sectionList == null){
        String sSections = getSharedPreferences(c).getString(PREFS_KEY_SECTIONS, null);

        if(sSections == null){
            return new ArrayList<>();
        }

        Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
        try {

            this.sectionList = new Gson().fromJson(sSections, sectionListType);

            if(this.sectionList == null){
                return new ArrayList<>();
            }
        }catch (JsonSyntaxException ex){

            return new ArrayList<>();

        }catch (JsonParseException exc){

            return new ArrayList<>();
        }
    }
    return this.sectionList;
}

这对我很管用。

其他回答

您可以将其转换为Map Object来存储它,然后在检索SharedPreferences时将值更改回ArrayList。

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();

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()
    }
}

您可以使用序列化或Gson库将列表转换为字符串,反之亦然,然后将字符串保存在首选项中。

使用谷歌的Gson库:

//Converting list to string
new Gson().toJson(list);

//Converting string to list
new Gson().fromJson(listString, CustomObjectsList.class);

使用Java序列化:

//Converting list to string
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(list);
oos.flush();
String string = Base64.encodeToString(bos.toByteArray(), Base64.DEFAULT);
oos.close();
bos.close();
return string;

//Converting string to list
byte[] bytesArray = Base64.decode(familiarVisitsString, Base64.DEFAULT);
ByteArrayInputStream bis = new ByteArrayInputStream(bytesArray);
ObjectInputStream ois = new ObjectInputStream(bis);
Object clone = ois.readObject();
ois.close();
bis.close();
return (CustomObjectsList) clone;

嘿,朋友们,我没有使用Gson库就得到了上述问题的解决方案。我在这里发布源代码。

1.变量声明,即

  SharedPreferences shared;
  ArrayList<String> arrPackage;

2.变量初始化,即

 shared = getSharedPreferences("App_settings", MODE_PRIVATE);
 // add values for your ArrayList any where...
 arrPackage = new ArrayList<>();

3.使用packagesharedPreferences()将值存储到sharedPreference:

 private void packagesharedPreferences() {
   SharedPreferences.Editor editor = shared.edit();
   Set<String> set = new HashSet<String>();
   set.addAll(arrPackage);
   editor.putStringSet("DATE_LIST", set);
   editor.apply();
   Log.d("storesharedPreferences",""+set);
 }

4.使用retriveSharedValue()检索sharedPreference的值:

 private void retriveSharedValue() {
   Set<String> set = shared.getStringSet("DATE_LIST", null);
   arrPackage.addAll(set);
   Log.d("retrivesharedPreferences",""+set);
 }

我希望这对你有帮助…