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JSON字符串,并将字符串存储在SharedPreferences中。
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();
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。
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());
}
}
public void saveUserName(Context con,String username)
{
try
{
usernameSharedPreferences= PreferenceManager.getDefaultSharedPreferences(con);
usernameEditor = usernameSharedPreferences.edit();
usernameEditor.putInt(PREFS_KEY_SIZE,(USERNAME.size()+1));
int size=USERNAME.size();//USERNAME is arrayList
usernameEditor.putString(PREFS_KEY_USERNAME+size,username);
usernameEditor.commit();
}
catch(Exception e)
{
e.printStackTrace();
}
}
public void loadUserName(Context con)
{
try
{
usernameSharedPreferences= PreferenceManager.getDefaultSharedPreferences(con);
size=usernameSharedPreferences.getInt(PREFS_KEY_SIZE,size);
USERNAME.clear();
for(int i=0;i<size;i++)
{
String username1="";
username1=usernameSharedPreferences.getString(PREFS_KEY_USERNAME+i,username1);
USERNAME.add(username1);
}
usernameArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, USERNAME);
username.setAdapter(usernameArrayAdapter);
username.setThreshold(0);
}
catch(Exception e)
{
e.printStackTrace();
}
}
使用这个对象——> TinyDB——Android-Shared-Preferences-Turbo非常简单。
TinyDB tinydb = new TinyDB(context);
把
tinydb.putList("MyUsers", mUsersArray);
得到
tinydb.getList("MyUsers");
更新
一些有用的例子和故障排除可以在这里找到:Android共享偏好TinyDB putListObject函数
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