So this question bothered me for a while because i can't seem to find out an easy, convenient and natural way to update ui while fetching data from external locations (Webserver).
I will sketch my scenario :
I got a webserver, which serves JSONArray's and JSONObject's. It always returns this because i don't like nullpointers. I tried to write a class which extends AsyncTask. I succeeded in doing this and it looks like this :
public class Server extends AsyncTask<String, Integer, Object>{
private String fetch_url;
private String return_type;
private Activity ct;
public Server() {
}
public Server(Activity ct) {
this.ct = ct;
}
@Override
protected void onPreExecute()
{
}
@Override
protected Object doInBackground(String... url) {
this.fetch_url = url[0];
this.return_type = url[1];
if(return_type.equals("json_object")) {
return urlToJsonObject(this.fetch_url);
} else {
return urlToJsonArray(this.fetch_url);
}
}
private String convertStreamToString(InputStream is) {
/*
* To convert the InputStream to String we use the BufferedReader.readLine()
* method. We iterate until the BufferedReader return null which means
* there's no more data to read. Each line will appended to a StringBuilder
* and returned as String.
*/
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return sb.toString();
}
protected JSONObject urlToJsonObject(String url) {
JSONObject arr = null;
HttpClient httpclient = new DefaultHttpClient();
// Prepare a request object
HttpGet httpget = new HttpGet(url);
// Execute the request
HttpResponse response;
try {
response = httpclient.execute(httpget);
// Get hold of the response entity
HttpEntity entity = response.getEntity();
if (entity != null) {
// A Simple JSON Response Read
InputStream instream = entity.getContent();
String result= convertStreamToString(instream);
// A Simple JSONArray Creation
arr = new JSONObject(result);
// Closing the input stream will trigger connection release
instream.close();
}
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return arr;
}
protected JSONArray urlToJsonArray(String url) {
JSONArray arr = null;
HttpClient httpclient = new DefaultHttpClient();
// Prepare a request object
HttpGet httpget = new HttpGet(url);
// Execute the request
HttpResponse response;
try {
response = httpclient.execute(httpget);
// Get hold of the response entity
HttpEntity entity = response.getEntity();
if (entity != null) {
// A Simple JSON Response Read
InputStream instream = entity.getContent();
String result= convertStreamToString(instream);
// A Simple JSONArray Creation
arr = new JSONArray(result);
// Closing the input stream will trigger connection release
instream.close();
}
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return arr;
}
}
After the data came in, i transform it to my own models with getters and setters. Then i want to update my ui with these results, but for some reason i always receive nullpointers.
For example :
- I got an GridLayout which i want to fill with multiple PhotoAlbums.
- First i am fetching those records from my webserver.
- Then processing each album.
- Then if an individual Album gets added to the GridLayout it needs to update. And not all at once while blocking ui.
What is a nice central way of getting data from external sources and updating ui while it is loading? Can somebody point me to techniques, tutorials, methods, insights, etc. I am very curious about this.
