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
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。
其他回答
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()
}
}
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。
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;
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。
在API 11之后,SharedPreferences Editor接受set。您可以将List转换为HashSet或类似的东西,并像这样存储它。当你把它读回来时,把它转换成一个数组列表,如果需要的话对它排序,你就可以开始了。
//Retrieve the values
Set<String> set = myScores.getStringSet("key", null);
//Set the values
Set<String> set = new HashSet<String>();
set.addAll(listOfExistingScores);
scoreEditor.putStringSet("key", set);
scoreEditor.commit();
你也可以序列化你的数组列表,然后将它保存/读取到SharedPreferences。解决方案如下:
编辑: 下面是将ArrayList作为一个序列化对象保存到SharedPreferences的解决方案,然后从SharedPreferences中读取它。
因为API只支持在SharedPreferences中存储和检索字符串(在API 11之后,它更简单),我们必须序列化和反序列化ArrayList对象,它将任务列表变成一个字符串。
在TaskManagerApplication类的addTask()方法中,我们必须获取共享首选项的实例,然后使用putString()方法存储序列化的ArrayList:
public void addTask(Task t) {
if (null == currentTasks) {
currentTasks = new ArrayList<task>();
}
currentTasks.add(t);
// save the task list to preference
SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
Editor editor = prefs.edit();
try {
editor.putString(TASKS, ObjectSerializer.serialize(currentTasks));
} catch (IOException e) {
e.printStackTrace();
}
editor.commit();
}
类似地,我们必须从onCreate()方法中的首选项中检索任务列表:
public void onCreate() {
super.onCreate();
if (null == currentTasks) {
currentTasks = new ArrayList<task>();
}
// load tasks from preference
SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
try {
currentTasks = (ArrayList<task>) ObjectSerializer.deserialize(prefs.getString(TASKS, ObjectSerializer.serialize(new ArrayList<task>())));
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
您可以从Apache Pig项目ObjectSerializer.java中获得ObjectSerializer类
推荐文章
- BottomSheetDialogFragment的圆角
- 在应用程序启动时出现“无法获得BatchedBridge,请确保您的bundle被正确打包”的错误
- 我如何改变默认对话框按钮的文本颜色在安卓5
- 更改单选按钮的圆圈颜色
- 如何在android中复制一个文件?
- adb找不到我的设备/手机(MacOS X)
- 如何在新的材质主题中改变背面箭头的颜色?
- androidviewpager与底部点
- 相同的导航抽屉在不同的活动
- 如何从视图中获得托管活动?
- 单一的TextView与多种颜色的文本
- 如何在非活动类(LocationManager)中使用getSystemService ?
- 检查ArrayList中是否存在值
- 在清单中注册应用程序类?
- Android:从数组中编程创建旋转器