Develop Reference

Handling Volley when no key exists

I have implemented Volley and Recycler view to parse and display a list of few items from a simple JSON file.
There are at times when a key doesnot exists in an object but may appear in other object. That key is already defined using object.getInt("someKey").
As soon as Volley starts parsing the object with the missing key, it breaks out of the for loop (objects are stored in array) and catches the JSONException e, which is exactly what the app is supposed to do in case of a missing key.
However, I would like to prevent this behavior and use a placeholder value for that missing key of that particular object, so that the array list gets successfully buildup and recyclerview gets filled thereby application starts working normally.
What logic can I use in order to achieve this behavior?
Thank you!
private void parseJSON() {
String url = "https://example.com/index.json";
JsonArrayRequest request = new JsonArrayRequest(Request.Method.GET, url, null,
new Response.Listener<JSONArray>() {
#Override
public void onResponse(JSONArray response) {
try {
for (int i = 0; i < response.length(); i++) {
JSONObject object = response.getJSONObject(i);
String title = object.getString("subject");
String description = object.getString("message");
String imageUrl = object.getString("thumb");
Integer threadId = object.getInt("threadId");
mList.add(new Item( title, description, threadId));
}
mItemAdapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
}
});
In the above code, threadId is the key, which may or maynot appear in many objects of the JSON.

You can check firstly if your key exists on object
try {
for (int i = 0; i < response.length(); i++) {
JSONObject object = response.getJSONObject(i);
String title = object.getString("subject");
String description = object.getString("message");
String imageUrl = object.getString("thumb");
Integer threadId;
if(object.toString().contain("threadId"){
threadId = object.getInt("threadId");
}else{
threadId = 0;
}
mList.add(new Item( title, description, threadId));
}
mItemAdapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}

If i understood well your Question , here what you need to do , if you are not sure if this key exists use the following
jsonObject.optBoolean("yourKey");
jsonObject.optInt("yourKey");
jsonObject.optString("yourKey");
jsonObject.optLong("yourKey");
jsonObject.optDouble("yourKey");
jsonObject.optJSONArray("yourKey");
this will make sure jsonObject will ignore that key if it doesn't exist.

object.getInt("someKey") is to get value from "somekey".if somekey is not appeared it shows JSONException. Instead of this object.optInt("someKey"). It will get value from "somekey" if it appears, otherwise it skipped. This is simple solution. Thanks

Hashmap to JSON Array

I would like to ask if someone here knows how to convert a HashMap to JSON Array to be used on a Adapter. The logic is when you logged in, it will fetch data on a web server using Volley, store it on SQLite database and at the same time it will show the retrieve data on a custom listview. The thing is, if you will move to another fragment on the application and then go back, it will request again on the volley which it will take time. I wanted that if you will go back the data stored on the SQLite database will be retrieved and if the user wanted to update the data using SwipeRefresh, that's the time to update for new data.
Here is my code.
public void LoadMarkets()
{
Map<String,String>tmpRate = new HashMap<String,String>();
RateDb db = new RateDb(getActivity().getApplicationContext());
Cursor rs = db.getData();
if(rs!=null && rs.getCount()>0)
{
if(rs.moveToFirst())
{
while(rs.moveToNext())
{
tmpRate.put("rateID",rs.getString(rs.getColumnIndex(RateDb.rateID)));
tmpRate.put("Name",rs.getString(rs.getColumnIndex(RateDb.rateName)));
tmpRate.put("Rate",rs.getString(rs.getColumnIndex(RateDb.rateRate)));
tmpRate.put("Date",rs.getString(rs.getColumnIndex(RateDb.rateDate)));
tmpRate.put("Time",rs.getString(rs.getColumnIndex(RateDb.rateTime)));
tmpRate.put("Ask",rs.getString(rs.getColumnIndex(RateDb.rateAsk)));
tmpRate.put("Bid",rs.getString(rs.getColumnIndex(RateDb.rateBid)));
tmpRate.put("Balance",rs.getString(rs.getColumnIndex(RateDb.rateBalance)));
//Log.d("MyDebug",rs.getString(rs.getColumnIndex(RateDb.rateName)));
}
}
}
rs.close();
db.close();
JSONObject jsonObject = new JSONObject(tmpRate);
JSONArray jsonArray = new JSONArray();
jsonArray.put(jsonObject);
RowAAdapter rowAAdapter = new RowAAdapter(getActivity(),jsonArray);
lvMarkets.setAdapter(rowAAdapter);
swipeRefreshLayout.setRefreshing(false);
}
The problem is that when i load this function, it only shows the last data.
I hope you can help me with my problem.
Thank you very much.

You can put the values directly into the jsonObject instead of adding it to the hashmap like this :
public void LoadMarkets()
{
RateDb db = new RateDb(getActivity().getApplicationContext());
Cursor rs = db.getData();
if(rs!=null && rs.getCount()>0)
{
if(rs.moveToFirst())
{
while(rs.moveToNext())
{
JSONObject jsonObject = new JSONObject();
jsonObject.put("rateID",rs.getString(rs.getColumnIndex(RateDb.rateID)));
jsonObject.put("Name",rs.getString(rs.getColumnIndex(RateDb.rateName)));
jsonObject.put("Rate",rs.getString(rs.getColumnIndex(RateDb.rateRate)));
jsonObject.put("Date",rs.getString(rs.getColumnIndex(RateDb.rateDate)));
jsonObject.put("Time",rs.getString(rs.getColumnIndex(RateDb.rateTime)));
jsonObject.put("Ask",rs.getString(rs.getColumnIndex(RateDb.rateAsk)));
jsonObject.put("Bid",rs.getString(rs.getColumnIndex(RateDb.rateBid)));
jsonObject.put("Balance",rs.getString(rs.getColumnIndex(RateDb.rateBalance)));
jsonArray.put(jsonObject);
//Log.d("MyDebug",rs.getString(rs.getColumnIndex(RateDb.rateName)));
}
}
}
rs.close();
db.close();
RowAAdapter rowAAdapter = new RowAAdapter(getActivity(),jsonArray);
lvMarkets.setAdapter(rowAAdapter);
swipeRefreshLayout.setRefreshing(false);
}
The problem with your code is that :
You're putting the values with keys "rateID", "Name"... etc. in the while loop again and again, so the previous values are being replaced with the new values and finally you've just one set of data in your hashmap. That's why you're getting only the last set of data.
Try the above code. It should work as expected.
This will work as it creates a new JsonObject in the loop and adds it to the jsonArray when the data is successfully added to it.

Returns zero for all values retrieved from the parse database

I'm using parse backend to store and retrieve the datas for my android app, the storing gets done properly but i have problem in retrieving it. I just went through the parse documentation to retrieve the result but what i get is just 0 for all the retrieved values..im suret that the class exists in the parse cloud with valid values but still i get 0 for all the queries.. this is my code to save:
Toast.makeText(getApplicationContext(),"writing to parse",Toast.LENGTH_SHORT).show();
ParseObject dataObject = new ParseObject("Score");
dataObject.put("correct",correctAnswers);
dataObject.put("wrong",wrongAnswers);
dataObject.put("percent", percentage);
dataObject.saveInBackground();
this is how i get back the saved data
ParseQuery<Score> query = ParseQuery.getQuery("Score");
try {
List<Score> scoreList = query.find();
} catch (ParseException e) {
e.printStackTrace();
}
query = ParseQuery.getQuery("Score");
final Activity ctx = this;
query.findInBackground( new FindCallback<Score>() {
#Override public void done(List<Score> scoreList, ParseException e) {
if ( e == null ) {
ParseObject dataObject = ParseObject.create("Score");
int p = dataObject.getInt("correct");
int q = dataObject.getInt("wrong");
int r = dataObject.getInt("percent");
Toast.makeText(ExamRecordActivity.this,String.valueOf(p),Toast.LENGTH_SHORT).show();
Toast.makeText(ExamRecordActivity.this,String.valueOf(q),Toast.LENGTH_SHORT).show();
Toast.makeText(ExamRecordActivity.this,String.valueOf(r),Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(ctx,
"Error updating questions - please make sure you have internet connection",
Toast.LENGTH_LONG).show();
}
}
});

Inside the done method you are creating a new by calling ParseObject dataObject = ParseObject.create("Score"); and then trying to read values from it without putting any in.
I don't know what the structure of your class is but you need to be iterating through List<Score> scoreList in order to get the queried data.

Android Hashmap issue

I have a piece of code which basically synchronises data between an online database. However I am getting an error on one particular line of code (map.put("id", obj.get(mydb.WEB_ID).toString());) where an integer value is obtained from the android sqlite databasse and submitted to the online database. The full cose is as displayed below :
public void updateSQLite(String response){
ArrayList<HashMap<String, String>> syncL;
syncL = new ArrayList<HashMap<String, String>>();
// Create GSON object
Gson gson = new GsonBuilder().create();
try {
// Extract JSON array from the response
JSONArray arr = new JSONArray(response);
System.out.println(arr.length());
// If no of array elements is not zero
if(arr.length() != 0){
// Loop through each array element, get JSON object which has userid and username
for (int i = 0; i < arr.length(); i++) {
// Get JSON object
JSONObject obj = (JSONObject) arr.get(i);
System.out.println(obj.get("web_id"));
System.out.println(obj.get("phone_id"));
System.out.println(obj.get("msg_id"));
mydb.updateWebSync(obj.get(obj.get("phone_id").toString(), obj.get("msg_id").toString(), obj.get("web_id").toString());
HashMap<String, String> map = new HashMap<String, String>();
map.put("id", obj.get(mydb.WEB_ID).toString());
map.put("p_id", obj.get(mydb.COLUMN_ID).toString());
map.put("s", "1");
syncL.add(map);
}
updateMySQLSyncSts(gson.toJson(syncL), "syncsts");
Toast.makeText(getApplicationContext(), "Download Messages success!", Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
Toast.makeText(getApplicationContext(), "Download Messages error!", Toast.LENGTH_SHORT).show();
e.printStackTrace();
}
}
In my android sqlite database, the value of mydb.WEB_ID is stored as an integer. Any assistance is appreciated.

Hashmap<String,String>
it only contains String values. So you have to convert it to String.
with using
toString()
function it ll give you error.
Try with
String.ValueOf(obj.get("web_id"))
it ll convert the interger value to String and your problem gets resolved.
Happy coding. :P

I figured out my mistake...I was calling the database column name in the HashMap which is different from the json variable. Thanks all for your assistance.

How to edit an item in a json file?

I have this structure that is generated by my application and I read in a listView:
[{
"phone": "202020",
"name": "Jhon",
"id": 10,
"age": 20
},
{
"phone": "303030",
"name": "Rose",
"id": 11,
"age": 22
}]
When I select an item in the listview, I open a screen form passing the values ​​of the clicked item.
lv.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
String age = ((TextView) view.findViewById(R.id.age)).getText().toString();
String phone = ((TextView) view.findViewById(R.id.phone)).getText().toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_AGGE, age);
in.putExtra(TAG_PHONE, phone);
startActivity(in);
}
});
This screen opens when you click on the item is a form where I put the values ​​passed from the previous screen fields.
My question is: When you click save in this form, I have to get the new values ​​and update the json file. How to do this?
Ex: I want to change the record ID 22, which is the user Rose.
ADD MORE INFORMATION:
I already use the Gson to generate items.
Code to generate:
btnSalvar.setOnClickListener( new View.OnClickListener() {
public void onClick(View v) {
gson = new GsonBuilder().setPrettyPrinting().create();
final File file = new File(Environment.getExternalStorageDirectory() + "/download/ibbca/auditar.json");
// to check if file exists before before it maybe will be created
if (file.exists())
fileExists = true;
try{
// create file or get access to file
raf = new RandomAccessFile(file, "rw");
if (fileExists) // start new file as an array
raf.seek(file.length() - 1);
else { // start writing inside the bracket
raf.writeBytes("[");
raf.seek(file.length());
}
UserTestJson obj1 = new UserTestJson();
obj1.setId(10);
obj1.setName("Jhon");
obj1.setAge(20);
obj1.setPhone("202020");
toJson(obj1);
// end file
raf.writeBytes("]");
raf.close();
}catch(FileNotFoundException f){
f.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
And the Class UserTestJson, i created with get and seters for each variable.

The Simplest way is, Just go to that json Object and set the desired value for the key.
JSONArray arr = new JSONArray(str);
for(int i = 0; i < arr.length(); i++){
JSONObject jsonObj = (JSONObject)arr.get(i); // get the josn object
if(jsonObj.getString("name").equals("Rose")){ // compare for the key-value
((JSONObject)arr.get(i)).put("id", 22); // put the new value for the key
}
textview.setText(arr.toString());// display and verify your Json with updated value
}

It's perhaps a good time to switch to an ArrayAdapter.
I recommend to transfer the JSON into a custom model bean first:
class Person {
long id;
String phone, name, age;
}
Then you can use an JSON parser library like gson to parse the array into a List<Person> and use this array to drive your list. (See Gson help with parse array - works without array but won't with array) for an example on the parsing.
Finally, when you are ready to write back the data, simply re-generate the JSON from the array. This question got an example for that: Trouble with Gson serializing an ArrayList of POJO's
Pros:
Once your JSON data model changes, only a small change in your model is needed to read the new format.
You can use standard Java tools like ArrayList and POJOs
Cons:
You will need to import GSON or equivalent into your project.
Also check this question: How to parse JSON in Android

I cant find a direct way to do so.
But you can use this function to solve the problem first. See if there is other solution
private JSONObject setJSONVal(JSONObject jsonObject, String index, String value) throws JSONException{
String jsonString = jsonObject.toString().trim();
jsonString = jsonString.replace("\"" + index + "\":\"" + jsonObject.getString(index) + "\"", "\"" + index + "\":\"" + value + "\"");
return new JSONObject(jsonString);
}