I have my own Objects which I need to store for later use. The User saves this object, it is turned into a JSON String, then when the User is connected to a network, the JSON String is turned back into the object operations are performed on it.
My problem is that, at run time, how do I know how to store the object?
i.e
Gson gson= new Gson();
String pointOfInterest = gson.toJson(point);
SharedPreferences.Editor sharedprefEditor = application_shared_preferences.edit();
sharedprefEditor.putString(?KEY?,pointOfInterest);
What can I use for the value of KEY? If I use an index, it will get reset every time I open or close the app, and this will replace my Objects.
Edit
Sorry I didn't make this clear enough, the method that the above code is in can be run an arbitrary number of times and there could be several pointsOfInterest to store.
First of all, if you use an index, the Preference will stay forever:
For instance:
sharedprefEditor.putString("JSON569",pointOfInterest);
You can also save the index in an other preference; for instance separated by a column:
sharedprefEditor.putString("indexes","569;789;852");
You can, easily check if an instance exists:
myPreference.getString("JSON789","").contentEquals("");
Or get all your instances:
for (int anIndex:indexes)
Log.i("TAG","Current value: "+myPreference.getString("JSON"+anIndex,""));
Please xplain a little bit more your question, I see no difficulties there/
You can name the key whatever you want, just make it consistent. One way to do it is make a constant in your class for it:
public class MyClass {
private static final String OBJECT_KEY = "myObjectKey";
...
Then when you save your object:
Gson gson= new Gson();
String pointOfInterest = gson.toJson(point);
SharedPreferences.Editor sharedprefEditor = application_shared_preferences.edit();
sharedprefEditor.putString(OBJECT_KEY,pointOfInterest);
When you load it, just use OBJECT_KEY to get a string out of the shared preferences:
String objectString = sharedPrefs.getString( OBJECT_KEY, "" );
Related
I have a shopping cart where I want to remove a product there, but I'm facing an issue. I can add product to the shopping cart and I save to shared preferences, but when I want to remove it but doesn't work. Here what I did:
holder.removeProduct.setOnClickListener(v -> {
SharedPreferences preferences = mContext.getSharedPreferences(ITEMS_PREF, Context.MODE_PRIVATE);
SharedPreferences.Editor mEditor = preferences.edit();
Gson gson = new Gson();
String json = preferences.getString("artikujtShporta", "");
ArrayList<Artikujt> artikullObject = gson
.fromJson(json, new TypeToken<ArrayList<Artikujt>>(){}.getType());
if (artikullObject != null) {
artikullObject.remove(artikulli);
String jsonString = gson.toJson(artikullObject);
mEditor.putString("artikujtShporta", jsonString);
mEditor.apply();
} else {
ArrayList<Artikujt> arrayArtikuj = new ArrayList<>();
arrayArtikuj.remove(artikulli);
Type listOfTestObject = new TypeToken<ArrayList<Artikujt>>(){}.getType();
String s = gson.toJson(arrayArtikuj, listOfTestObject);
mEditor.putString("artikujtShporta", s);
mEditor.apply();
}
});
The same thing I did for adding the product, with the difference that here I call
artikullObject.remove(artikulli);
What i'm missing?
What is the problem?
The problem here will be that the instance of your class Artikujt which you want to delete from the Array is not the same as you have read out of the Preferences.
As soon as you use Gson to make your String to a new Array it will generate completely new instances of your class and obviously these will not be the same as you had before. Maybe they are equal, but they are not the same instances.
What can you do to solve this?
I am assuming that you want to have each Artikujt only once. What means you could also use a HashSet. The advantage of this is it would would use the hashCode() function to determine which instance in the set you want to remove. So you just need to override this hashCode() function in your model class and use all of its properties to calculate the hashcode. You can find a example here: https://www.sitepoint.com/how-to-implement-javas-hashcode-correctly/
Sidenote
Your else block is unnecessary. It doesn't make a lot of sense. You are creating a empty ArrayList, then you remove sth from this empty list and then you save this empty List into the shared preferences. The logic of your code wouldn't change if you would just remove this else block.
I have a probleme here.
I don't know how to read all values of a SharedPreferences for one particular key.
Actually I'm trying to write an Arraylist in preferences , then read it.
Let me explain with some code, Here is my methods for write in preferences :
fun writeArrayOnPreferences(key: String?, array: ArrayList<String>, c:Context) {
val preferences = c.getSharedPreferences(
c.getString(key), Context.MODE_PRIVATE)
with(preferences.edit()) {
for (value in array) {
putString(key, value)
}
commit()
}
}
My writing code works , it's persistent , but I don't really understand how to READ this Arraylist from preferences.
I tried a lot of things to read this but it show me only the last element wrote in preferences
I really want you to understand that I want multiple values for a specific key
This is a quick example based on Nabin Bhandari's answer
fun writeArrayOnPreferences(key: String, array: ArrayList<String>, c:Context) {
val jsonString = Gson().toJson(array)
pref.edit().putString(key, jsonString).commit()
}
fun readArrayFromPreferences(key: String, c: Context): ArrayList<String> {
val jsonString = pref.getString(key)
val array = Gson().fromJson(jsonString, ArrayList<String>()::class.java)
return array
}
ok here how it is! If you want multiple data against one key in share pref editor then SET is your solution as After API 11 the SharedPreferences Editor accept Sets. You could convert your List into a HashSet or something similar and store it like that When your read it back, convert it into an ArrayList, sort it if needed and you're good to go.
//Set the values
val yourSet = HashSet<String>()
set.addAll(listOfExistingScores)
yourPrefEditor.putStringSet("key", yourSet)
yourPrefEditor.commit()
//Retrieve the values
val yourSet = yourPref.getStringSet("key", null)
SOLUTION NUMBER 2
would be like serializing the ArrayList and passing it! but there can be a catch if any value in your array does posses any rule that can't be Parced it will crash!
For More check this Thread this is in java but it will help tell you more!
You cannot simply loop values in an ArrayList put them in the preferences using same key for all values and expect to retrieve the ArrayList back.
You can convert the 'ArrayList' in JSON format and store it in SharedPreferences. Then to parse the JSON string to get the ArrayList.
You can make this process easier with the help of a library called Gson.
Try this:
with(preferences.edit()) {
var s = ""
for (value in array) {
s = s + value + ","
}
putString(key, value)
commit()
}
your array will be saved like comma separated values which when read back in a string, by using the split function will become an array.
In my app, I need some data that I do not want to request every time from the server.
This dat includes the userId and some array string.
I think I can store the user id in the SharedPreferences,
but what about the array?
Is it OK to use static variables?
You also can serialize your array to save a array as string in preferences, but keep in mind that if it was big, use Sqllite...
Or you can use the firebase with offline function.
You can use Gson parse Array to String and save to shared preferences.
When you read String from shared preferences you can use Gson to convert String to Array.
Gson library
ArrayList<String> yourArrayStr = convertArrayToString(yourArray);
SharedPreferences prefs = context.getSharedPreferences("PREFERENCE_NAME",
Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putString("array_key_name", yourArrayStr);
editor.apply();
function: convertArrayToString
private String convertArrayToString(ArrayList<String> yourArray){
Gson gson = new Gson();
return gson.toJson(yourArray);
}
function convertStringToArray when you read String from shared preferences
private ArrayList<String> convertStringToArray(String yourArrayStr){
Gson gson = new Gson();
return gson.fromJson(yourArrayStr , new TypeToken<ArrayList<String>>(){}.getType());
}
Good luck!
First of all create a class model. like this
public class User implements Serializable {
#SerializedName("id")
private int id;
#SerializedName("array")
private ArrayList<String> array;
//your get/set are here too
}
I use gson to make my life easier.
Than on your server response save the Json on your SharedPreference
SharedPreferencesUtils.write(Constants.Preferences.Keys.USER_DATA, userJson);
And finally everytime you need to read this information you use
String json = SharedPreferencesUtils.read(Constants.Preferences.Keys.USER_DATA, null);
User user = new Gson().fromJson(json, User.class);
I would load this information on your singleton to use everywhere i need it in the application :)
If you need to update it.. just get the response and save again on your SharedPreference.
I want to store an ArrayList<class> in shared preference. But the error showed up in editor3.putString("Array", nama);. I guess the error caused by putString. What sould i do?
Should I used another method to storing arraylist ?
ArrayList<Class> nama = new ArrayList<Class>(9);
nama.add(dragsandal.class);nama.add(Terimakasih.class);
nama.add(Ludah.class);
nama.add(Permisi.class);
nama.add(Tolong.class);
nama.add(Maaf.class);
SharedPreferences pref3 = getApplicationContext().getSharedPreferences("Array", MODE_PRIVATE);
SharedPreferences.Editor editor3 = pref3.edit();
editor3.putString("Array", nama);
editor3.apply();
You should use putStringSet(Set<String>) to store sets (Lists with unique elements). SharedPreferences do not provide a method to store lists directly.
You can easily convert your list to a set using e.g. new HashSet<String>(yourList);
If you need to store a list, you can serialize your list to a String, e.g. by using Gson and storing the json value. Then putString(json) would be correct.
First I don't think there is a way to store lists in Shared preferences. Second it is not a good idea. In your case,I would consider using Sqlite database. It would make things easier.
You can't store a Class type object in SharedPreferences. Also you can't store Lists. If you really need to, you can store the full name of the class object as a String. Then when you read the value back you, you can use Class.forName() to convert that string back to a class. It seems weird, but you can do it.
You could try this to save and restore a set of class names:
Set<String> set = new HashSet<String>();
set.put(Terimakasih.class.getName());
set.put(Ludah.class.getName());
set.put(Permisi.class.getName());
set.put(Tolong.class.getName());
set.put(Maaf.class.getName());
SharedPreferences pref3 = getApplicationContext().getSharedPreferences("set", MODE_PRIVATE);
SharedPreferences.Editor editor3 = pref3.edit();
editor3.putStringSet("set", set);
editor3.apply();
Set<String> strings = pref3.getStringSet("set", Collections.emptySet());
Set<Class> classes = new HashSet<Class>();
for (String s : strings) {
classes.put(Class.forName(s));
}
EDIT:
OK It turns out this code was working (more or less) I'd left in a line that reset the booleans I was trying to change. Thanks everyone for the help though.
Having trouble using SharedPreferences to read in saved array data when my app starts.
My _dPad Boolean and my _FreePlay Integer loads, saves and passes to and from my _renderer without any problems.
The trouble starts when I try and use some arrays
easteregg[] only has 2 entries right now so obviously I could just just turn them into separate variables but I wish to add more arras of longer length so this makes a convenient test example.
I've noted on the code what appears to happen (the easteregg[] settings just doesn't appear to have changed)
to read data:
// Read saved preferences
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
_renderer._dPad = prefs.getBoolean("_dPad", false); // * works ok *
_renderer._FreePlay = prefs.getInt("_FreePlay", 1); // * works ok *
_renderer.easteregg[0] = prefs.getBoolean("easteregg[0]", false ); // * not working
_renderer.easteregg[1] = true; // * even this is not working
setRenderer(_renderer);
to write data:
public void onDetachedFromWindow() {
super.onDetachedFromWindow();
// As good a time as any to save current config
save = false ; // don't commit if nothing changed.
SharedPreferences prefs =
PreferenceManager.getDefaultSharedPreferences(getContext());
SharedPreferences.Editor editor = prefs.edit();
if (_renderer._dPad != prefs.getBoolean("_dPad",false)){ save = true ;
editor.putBoolean("_dPad", _renderer._dPad);}
if (_renderer._FreePlay != prefs.getInt("_FreePlay",1)){ save = true ;
editor.putInt("_FreePlay", _renderer._FreePlay);}
editor.putBoolean("easteregg[0]", _renderer.easteregg[0]);
editor.putBoolean("easteregg[1]", _renderer.easteregg[1]);
if (save == true){editor.commit();}
}
And in the .renderer class
// START SAVE DATA
public boolean _dPad ; // false no Virtual Pad *Works Fine*
public int _FreePlay ; // 1 = no free play *Works Fine*
public boolean[] easteregg = new boolean[2]; *Values don't load or save*
//public boolean easteregg[]; // tried this first *CAUSES CRASH*
// END SAVE DATA
Do I have to convert the arrays to strings? I don't get how to change them.
I put your code into a quick activity, creating just the shell of the renderer class as you have above and found that your save boolean is false, so it never commits the preferences.
I forced the save to true, and played around with it and everything worked fine from there.
I'd recommend adding checks to the easter eggs the same as you have for any other preference; test to see if the current value is the same as the saved value, and if not, set the save flag.
I would suggest saving the array as a string in a single variable. It appears you have an array of booleans. So loop through it to make it a series of either ints (0, 1) or the string "true" or "false" then save it to an int or string.
I suspect the probelm might be that your setting name contains square brackets. I think that in key value names, the key name must be a valid variable name. And square brackets are not allowed in variable names.
However i would also expect this to throw an error. Does the code work if you name you settings "easteregg_01" and "easteregg_02"?
The best solutions would be to convert your array into JSON string and store it as preference value. If you have small amount of data, you can as well stick with org.json classes provided by android. If you have more data, GSON pull parser would be better, as it utlizes pull parser. And if you are really lazy, you grab my small databinding library and do:
String jsonState = preferences.getString(GAME_STATE, null);
StateStorage storage = JSONUnmarshaller.unmarshall(new JsonReader(new
StringReader(jsonState)), StateStorage.class);
and it will instantiate java class for you and fill in the data. And to save:
SharedPreferences.Editor editor = getPreferences(MODE_PRIVATE).edit();
StringWriter writer = new StringWriter();
JsonWriter jsonWriter = new JsonWriter(writer);
JSONMarshaller.marshall(jsonWriter, ss);
editor.putString(GAME_STATE, writer.toString());
editor.commit();
Databinding library is available on github, or from maven central:
https://github.com/ko5tik/jsonserializer
PS: at the moment I work on injection of preference values ( at the moment primitives only):
https://github.com/ko5tik/andject