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
您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。
我的utils类保存列表到SharedPreferences
public class SharedPrefApi {
private SharedPreferences sharedPreferences;
private Gson gson;
public SharedPrefApi(Context context, Gson gson) {
this.sharedPreferences = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
this.gson = gson;
}
...
public <T> void putList(String key, List<T> list) {
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(key, gson.toJson(list));
editor.apply();
}
public <T> List<T> getList(String key, Class<T> clazz) {
Type typeOfT = TypeToken.getParameterized(List.class, clazz).getType();
return gson.fromJson(getString(key, null), typeOfT);
}
}
使用
// for save
sharedPrefApi.putList(SharedPrefApi.Key.USER_LIST, userList);
// for retrieve
List<User> userList = sharedPrefApi.getList(SharedPrefApi.Key.USER_LIST, User.class);
. 我的utils的完整代码//检查使用实例的活动代码
public static void WriteSharePrefrence1(Context context, String key,
ArrayList<HashMap<String, String>> value)
{
final SharedPreferences preferences =
PreferenceManager.getDefaultSharedPreferences(context);
SharedPreferences.Editor editor = preferences.edit();
Gson gson = new Gson();
String json = gson.toJson(value);
editor.putString(key, json);
editor.commit();
}
public static ArrayList<HashMap<String, String>> ReadSharePrefrence1(Context context,
String key)
{
String data;
Gson gson = new Gson();
ArrayList<HashMap<String, String>> items = new ArrayList<>();
final SharedPreferences preferences =
PreferenceManager.getDefaultSharedPreferences(context);
final SharedPreferences.Editor editor = preferences.edit();
data = preferences.getString(key, "");
Type type = new TypeToken<ArrayList<HashMap<String, String>>>() {}.getType();
items = gson.fromJson(data, type);
return items;
}
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。
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 !!:)
推荐文章
- 警告:API ' variable . getjavacompile()'已过时,已被' variable . getjavacompileprovider()'取代
- 安装APK时出现错误
- 碎片中的onCreateOptionsMenu
- TextView粗体通过XML文件?
- 如何使线性布局的孩子之间的空间?
- DSL元素android.dataBinding。enabled'已过时,已被'android.buildFeatures.dataBinding'取代
- ConstraintLayout:以编程方式更改约束
- PANIC: AVD系统路径损坏。检查ANDROID_SDK_ROOT值
- 如何生成字符串类型的buildConfigField
- Recyclerview不调用onCreateViewHolder
- Android API 21工具栏填充
- Android L中不支持操作栏导航模式
- 如何分裂()一个分隔字符串到一个列表<字符串>
- 如何在TextView中添加一个子弹符号?
- PreferenceManager getDefaultSharedPreferences在Android Q中已弃用