Develop Reference

use stored JSON instead of Core Data

There are lots of tutorials out there describing how to fetch JSON objects from the web and map them to Core Data.
I'm currently working on an iOS (later: Android as well) app which loads json objects from web and displays them to the user. In my opinion all this mapping from and to Core Data is an overhead in this case, it would be much easier to save the JSON objects directly and use them as "cache" in the app. Are there libraries/documented ways how to achieve fetching json objects, save them locally and fetch them with a predefined identifier?
I would love to fetch e.g. 10 objects, show them to the user and save the data locally. The next time the user is on that list the local data is shown and in the background the json-file is fetched again to be up-to-date. I guess this is a common use case but I didn't find any tutorials/frameworks enabling exactly this.

You can simply use NSURLCache to cache http responses instead saving JSONs
http://nshipster.com/nsurlcache/

There are many ways to implement this. You can implement cache using either file storage or database depending on the complexity as well as quantity of your data. If you're using files, you just need to store JSON response and load it whenever activity/fragment is crated. What I have done sometimes is store the JSON response in the form of string in a file, and then retrieve it on activity/fragment load. Here's an example of reading and writing string files:
Writing files:
FileOutputStream outputStream = context.openFileOutput("myfilename",Context.MODE_PRIVATE);
String stringToBeSaved = myJSONObject.toString();
outputStream.write(stringToBeSaved.getBytes());
Reading from files
FileInputStream inputStream= context.openFileInput("myfilename");
int c;
String temp="";
while( (c = inputStream.read()) != -1){
temp = temp + Character.toString((char)c);
You can convert this string to JSONObject using :
JSONObject jsonObject = new JSONObject(temp);
Or you can use the string according to your needs.

What is the best way to store parsed json data

i would like to ask, how to store json data. I have a JSON file, which i parse using JSON Library. Now i got the data from a file. But i want to store them and show them later again.
The question is, whats the best way to store data? And is it even worth to store them?
I'm thinking about sql database, because its simple and most used.
Official android docs have few examples, so far i searched but if u have better guide, let me know.
Thank you! :)
EDIT1:
Ok, i have json file with data, which i can add to my app using RAW resources. Those data wont change, its a list of recipes, i dont have to download it. I can read the data like this:
InputStream is = mContext.getResources().openRawResource(R.raw.package_01);
Writer writer = new StringWriter();
char[] buffer = new char[1024];
try {
Reader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
int n;
while ((n = reader.read(buffer)) != -1) {
writer.write(buffer, 0, n);
}
is.close();
//catchblock
.....
}
and then i can parse the data trought JSONLibrary like this:
try {
//representing []JSON
JSONArray jsonArray = new JSONArray(writer.toString());
if(jsonArray != null){...}
...}
Im sending a HashMap to ListView, which includes name and id. And if the user clicks the ListView/GridView item, there is new Activity started, which shows all parsed data. I need to get match those parsed data with the id.
There are about 200 recipes in the file. The data are parsed on start of the Activity, while Splashscreen is displayed. I´m not sure, if its good idea to parse the data everytime when app starts.
So, is it effitient to parse data everytime the app starts? And if yes, how to keep the parsed data "together"? Should i use HashMap?
I hope i clarified my question :) Thanks for help.
EDIT2:
So after i knew what to do, i tried the suggested solution to use HashMap. Problem was there i got Failed Binder Exception. I have images encoded in Base64, that means i have a very long String, example here. That is a lot of data, there is limit:
The Binder transaction buffer has a limited fixed size, currently 1Mb, which is shared by all transactions in progress for the process.
I´ve tried to save it to
Set<String> titles = new HashSet<String>();
and then to SharedPreferences but the data for each recipe gets mixed.
**So, here it comes again, should i save the data to SQLite database or is there another effective option i can use? **
Thank you!

It really depends on a number of things like: How much data do you have now, how much will you have later, how complicated is the data. You could use something as simple as an array or hashmap; or something as complex as a database. You need to consider what you are trying to do , and find the simplest solution. If you are trying to persist data, you could use shared preferences, database, and internal/external storage (options outlined here).
Without more information it's hard to say what exactly to do. Keep it simple though. If you are getting JSON from a web service, I'd use an ArrayList or HashMap to store the data, rather than persisting it. It is simpler to implement and does the job.
EDIT:
To answer your question: Yes, using a HashMap and parsing each time is fine. You only have 200 fields, and you don't have images, so the time it will take to parse is minimal. Regardless of how you store the data, there is going to some level of "parsing" done. For example, if you store the data in a database, you are going to have to still pull the data, and put it into a HashMap.

Importing data at initial start of application in Android?

I need some text data (street names of a 2 million town) to get into my android application. I think the best way to do this is to store it into a sqlite database read-only when it starts the first time. As I read, doing this with a pre-defined database is pretty tedious and not clean but you have to copy it from external storage or something and have the data twice then. So I thought about using a CSV file from raw resources and delete it after import, but this is not possible too because this data will be built into the sdk file and can't be deleted any more.
My target is it to make some kind of initial data transfer from local and delete this data source. Any ideas how to achieve that properly? I'd like to go without downloading the data from a server because this would mean that the only reason my application needs an internet connection is because of downloading the initial data. Otherwise it wouldn't need an internet connection.

What about putting the .csv file in you asset folder and read it.
String next[] = {};
List<String[]> list = new ArrayList<String[]>();
try {
CSVReader reader = new CSVReader(new InputStreamReader(getAssets().open("test.csv")));
for(;;) {
next = reader.readNext();
if(next != null) {
list.add(next);
} else {
break;
}
}
} catch (IOException e) {
e.printStackTrace();
}

I'm thinking I'd compress the data in the initial installation resource and expand it on install. This answer sees to reference a 7zip open source java api.
Data compression on Android (other than java.util.zip ?)

Meanwhile I know that the data I will use in my app is too complex to populate the data by hand. Moreover the app needs internet access at any rate, so I will use a Json string to get the data.

Read JSON from /assets folder into an ArrayList in Android?

First, I have researched this question a lot. I learned how to read from my text file in the assets folder. The problem is that I don't want to end up with a string because the file is actually an arraylist written using json and inside that arraylist are objects. I need to access one object only. Here's what I mean:
I have a Book class, which has an int called chapter, an int called title, and an int called pageNum. I created several Book objects and added them to an ArrayList. Then I used the following code to write my ArrayList to a text file (in a regular java project):
ArrayList<Book> aList = new ArrayList<Book>();
aList.add(book1);
//etc...add more Book objects here...
File aFile = new File("books.txt");
FileOutputStream aFileStream = new FileOutputStream(aFile);
JSONOutputStream jsonOut = new JSONOutputStream(aFileStream);
jsonOut.writeObject(aList);
jsonOut.close();
That code creates a text file which I then put into the /assets folder in my Android project because I want it included with the app. In a non-Android java project I could simply use the following code to repopulate an ArrayList so that I could parse Book obects from specific indexes:
File bFile = new File("books.txt");
FileInputStream bFileStream = new FileInputStream(bFile);
JSONInputStream jsonIn = new JSONInputStream(bFileStream);
Arraylist<Book> bList = (ArrayList<Book>) jsonIn.readObject();
Book aBook = bList.get(253); //some arbitrary index
The json code I'm using comes from quickconnectfamily.org. You have to add a file called qc_json.jar to the build path of your project. http://www.quickconnectfamily.org/qcjson/more.html
The problem in Android is when I read the file using InputStream, I can only get the entire file into a string, the code above doesn't work in Android. I can't wrap JSONInputStreams around an InputStream, only around a FileInputStream. But it seems I am unable to use
FileInputStream.
So what I need is a way to create an ArrayList rather than a string in my Android app.
Without giving away too much about my app, the app basically generates a random number and creates a Book object from that index in the ArrayList. Then the user is quizzed with info from that specific book. Sounds silly, but the real app is much cooler.
I'm open to solutions, alternative methods of storing objects in a text file, etc. Please don't simply post criticism about my grammar, syntax, or application idea. I'm pretty new to app development and I couldn't care less about personal opinions. If anyone wants to see
more code I can upload it, but it doesn't seem necessary at this point. Thanks.

I figured out the solution. I connected my Evo 4G and tested the app and it worked. Here's what I did:
I used the following method to read from the file, which is what I was doing before:
InputStream is = appContext.getAssets().open("books.txt");
int size = is.available();
buffer = new byte[size];
is.read(buffer);
is.close();
String bufferString = new String(buffer);
When you do this, you end up with a String of the entire file. This is what I was able to do before, but what I wanted was a way to convert the String to an ArrayList of Book objects. Here's how I accomplished this:
//convert string to JSONArray
jsonArray = new JSONArray(bufferString);
//parse an Object from a random index in the JSONArray
JSONObject anObject = jsonArray.getJSONObject(randomNum);
Book aBook = new Book();
aBook.setTitle((String) anObject.get("title"));
//you can continue to set the different attributes of the Book object using key/value pairs from the Book class (e.g. setPageNum, setChapter, etc).
I don't know, maybe that was obvious to some people, but I really couldn't find any examples that did this. In a different question someone mentioned using the json library native to Android org.json and so I tried that and it worked.

Create list in android app

I want to know a good way to create a list in my android app. I have all info in my DB and want to load data from it each time I start the app and make a list from it (id and title).
What is the best approach?
Should I make a PHP-script that responds with a JSON encoded array with all list items or should I make an XML-file that generates each time the data in the DB changes that I import to the app each time it starts? or any other good way to do it?
Since all stuff are made by XML-files in android it feels like importing a XML would be a good thing, is it? And how do I import an XML-file from a web server into the app?
// Daniel

You can use either JSON or XML.
You can use the web service approach or you can include your db with your application.
In fact, I most often choose to create a sqlite3 database of my data and include it in the assets folder, which can be copied to the app's data folder on startup.
As for copying your sqlite3 database from assets/ to the db data directory, I found these instructions helpful.

In your situation I would pick JSON over XML for all the reason's stated in the following post: http://ajaxian.com/archives/json-vs-xml-the-debate
Plus, in android, there are JSON Array's built in by default so you don't have to do any extra passing of the code.
return new JSONArray("my json string goes here...");
Since we are talking about a mobile device, I would always generate changes in your php script rather than have a full sync as this will be a lot smaller in size that a full sync. However, you will need to give your user a option to do a full re-sync if this is applicable to your app. I would use a SQLite database to store the data and only update the changes in that.
To also make the stream smaller, you can gzip compress your output from php as this can be natively read by the android device. In my app, I compress 500kb down to ~110kb before transmitting, a huge saving on performance. Here a partial example of how to read the stream:
InputStream in = null;
HttpURLConnection httpConn = null; // you will have to write your on code for this bit.
if (httpConn.getContentEncoding() != null)
{
String contentEncoding = httpConn.getContentEncoding().toString();
if (contentEncoding.contains("gzip"))
{
in = new GZIPInputStream(httpConn.getInputStream());
}
}
else
{
in = httpConn.getInputStream();
}
I hope that this all makes sense, it's been a long day programming :)
Stu