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);
}

其他回答

使用Kotlin,对于简单的数组和列表,你可以这样做:

class MyPrefs(context: Context) {
    val prefs = context.getSharedPreferences("x.y.z.PREFS_FILENAME", 0)
    var listOfFloats: List<Float>
        get() = prefs.getString("listOfFloats", "").split(",").map { it.toFloat() }
        set(value) = prefs.edit().putString("listOfFloats", value.joinToString(",")).apply()
}

然后轻松访问首选项:

MyPrefs(context).listOfFloats = ....
val list = MyPrefs(context).listOfFloats
//Set the values
intent.putParcelableArrayListExtra("key",collection);

//Retrieve the values
ArrayList<OnlineMember> onlineMembers = data.getParcelableArrayListExtra("key");

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();

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);
}

您还可以将数组列表转换为String并优先保存

private String convertToString(ArrayList<String> list) {

            StringBuilder sb = new StringBuilder();
            String delim = "";
            for (String s : list)
            {
                sb.append(delim);
                sb.append(s);;
                delim = ",";
            }
            return sb.toString();
        }

private ArrayList<String> convertToArray(String string) {

            ArrayList<String> list = new ArrayList<String>(Arrays.asList(string.split(",")));
            return list;
        }

您可以使用convertToString方法将数组列表转换为字符串后保存它,并使用convertToArray方法检索字符串并将其转换为数组

在API 11之后,你可以直接保存设置到SharedPreferences !!:)