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.
Related
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.
In my app I have to send a big dataset back to our server for processing. I am using ksoap for all my requests to pull stuff from the server with your normal xml properties and attributes but in the one call I have to use a dataset to send information.
Is there anything in the ksoap library for android that makes this whole process easier?
basically right now I am just constructing this huge string with all these header,tags and a shcema
example:
String header = "<mmAps diffgr:id=\"mmApps"+String.valueOf(count)+"\" msdata:rowOrder=\"0\" diffgr:hasChanges=\"inserted\">\n";
String ecmmaID = "<ECMMAID>"+c.getString(c.getColumnIndex(Apparatus.APP_ECMMAID))+"</ECMMAID>\n";
etc..
String datasetToSend = header+ecmmaID+....;
and then I would make the request passing in the big string
Please tell me there is some sot of easier way to do this.
Also changing away from data sets is not a possibility since its out of my control
JSON is the best option that you can use easily with KSOAP. This would be structured and far more better than your generated string.
1. Make identical Model class in android and your server (C#.Net, Java, etc.)
// In Android
class MyData {
String someThing;
public getSomeThing() {}
//...
}
2. Encode that dataset to JSONArray in android using model class
// Create JSON Objects in loop for entire dataset
JsonObject jo = new JsonObject();
jo.add(myData.getSomthing());
// Add all JSON Objects in JSONArray
JSONArray jArray = new JSONArray();
jArray.add(jo);
3. Send this JSON as string using KSOAP
String toSendViaKsoap = jArray.toString();
4. Decode that string from json to list of model class on server.
Depending on your server language, decode that string and create objects of similar class of step 1 in native language here, and do whatever you want.
If you have .NET server application, there are lots of free libraries to dacode json inclulding builting json support as well. but I will prefer this one.
Hope this helps..:)
I have to submit data from 30 pages into the server.These datas from 30 pages are to be made into a single string and that i have to upload that single string into the server using json.
Each page may contain many answers tht may be either in plain text(value we receive from edit text),from check boxes(yes or no) and so on.....please suggest me a way to add all these data into a single string and upload it using json.
Based on the comment I suspect that you believe that you need to treat these "pages" as strings that you concat. However, what I think you're overlooking is that JSON is pretty versatile in how you add objects to it.
So, let's say you have the thing that you want to ship to your server and you call it
JSONObject myEntireFile = new JSONObject();
you can now add stuff to it at any time like this...
JSONObject page1 = new JSONObject();
myEntireFile.put("page1", page1);
meanwhile you can put whatever you want IN page 1 (cause that's just another serialized container).
You can keep doing this until you're ready to send it, at which time you just call
myEntireFile.toString();
which will convert your object into one long, well formatted, JSON string, that you can then open store for later use.
Heres my situation:
I have a RESTful WCF service running on my server, the service is meant to get various types of data about people from a database and makes that data available as a single JSON object. It works great!
[EDIT]There is another service that maintains an image cache in the file system on the server. When a request is sent to the RESTful service, that service then requests an image from the image service. If the image is already in the cache (same width, height and person as the request), it returns that (as a byte array). We MUST use this service to retrieve images.
Now what I want is the image of that person. In our database, the image is a long raw (ew). However, I have dealt with that issue already (previous paragraph). The image is now a Byte array. I am pretty new to android and I am not sure what the best way to retrieve this image is. What I thought I could do was add the byte array to the JSON object and then use the base64 decoder to convert it into a drawable image. However, everytime I try, it times out and tells me it expected ',' or ']' at some arbitrary index of the char buffer for the JSON object.
I have been able to pull the small bits of data out of the JSON object without an issue, but now that there is a huge byte array in it, the JSONObject hates me. What would be a better way to get this image from my service?
Base64 encode the byte array to get a string.
Add the string to JSON object and send it.
When JSON is received, get out the string.
Base64 decode it to get back the byte array.
Use byte array to create Image.
See this question on storing images, it's always better to store this sort of data on file system. If possible deprecate that field, and create a script to move existing images to file system.
You should then store the images on a file system (or some sort of content management system) which can be retrieved by a URL.
Then store the URL in the database. you can then send this in your json object.
{
...
image_url:<url from database>
...
}
When the client receives this it will make a call to that URL and download the image.
Your client will have to make a separate call to retrieve the image but it's generally better than filling your database with binary data. This can also work to your advantage if you want to display data fast while allowing the image to be downloaded in the background.
Better than using Base64 encoding is this way of returning Stream (from WCF RAW programming)
[OperationContract, WebGet]
public Stream GetTestImage(Image image)
{
MemoryStream stream = new MemoryStream();
image.Save(stream, System.Drawing.Imaging.ImageFormat.Jpeg);
stream.Position = 0;
WebOperationContext.Current.OutgoingResponse.ContentType = "image/jpeg";
return stream;
}
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