Develop Reference

android - Starting an event with the completion of two threads running parallel

I have two or more network calls in separated threads on main activity start, I want to show all data after network threads done.
Thread firstNetworkCallThread=new Thread(new Runnable() {
#Override
public void run() {
// network calls and get data...
}
});
Thread secondNetworkCallThread =new Thread(new Runnable() {
#Override
public void run() {
// network calls and get data...
}
});
firstNetworkCallThread.start();
secondNetworkCallThread.start();
I want these threads work parallel, and when both of them are complete, call new event to show data.
How can I do this?

Guava has a good solution for this. If you convert your Threads to ListenableFutures (also a Guava object) you can create a list of ListenableFutures and add a callback to that list.
Futures.addCallback(
Futures.allAsList(/*future1*/, /*future2*/, /*future3*/),
new AbstractDisposableFutureCallback<List<Object>>() {
#Override
protected void onSuccessfulResult(List<Object> results) {
// whatever should happen on success
}
#Override
protected void onNonCancellationFailure(Throwable throwable) {
// whatever should happen on failure
}
});
Guava also has a bunch methods such as #successfulAsList which only contains successful results or #inCompletionOrder which orders them based on when they completed and a bunch of others.
I generally tend to use Guava as it provides a fairly clean solutions to problems like these.
An example of how to creates a ListenableFuture is as follows:
ListeningExecutorService service = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));
ListenableFuture<Object> explosion =
service.submit(
new Callable<Object>() {
public Object call() {
// get network data
return null; // return the data
}
});

Leak : Timer and TextWatcher

I'm working on an editText and a recyclerView.
My recyclerView is updated when I write letters in my EditText.
I put a Timer inside my textWatcher in order to avoid sending requests each time user write a letter.
searchDestinationEt.addTextChangedListener(new TextWatcher() {
#Override
public void beforeTextChanged(final CharSequence s, final int start, final int count, final int after) {
//There is nothing to do here
}
#Override
public void onTextChanged(final CharSequence s, final int start, final int before, final int count) {
if (timer != null) {
timer.cancel();
}
}
#Override
public void afterTextChanged(final Editable s) {
timer = new Timer();
//we schedule this in order to avoid sending useless request.
//We wait the user is finishing writing before sending requests
timer.schedule(new TimerTask() {
#Override
public void run() {
((Activity) context).runOnUiThread(new Runnable() {
#Override
public void run() {
actionsListener.onDestinationSearch(s.toString());
}
});
}
}, DELAY_SEND_REQUEST);
}
});
It works well but leakcanary says that I have a leak in this part of code.
Any idea ?

Sorry for being late with the response, but did you try separating textwatcher like this ?:
TextWatcher for more than one EditText

Why do you use Timer and TimerTask for delayed, not recurring action? The easiest and the common way is to use just a regular Handler with postDelayed():
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//do somthing here
}
}, DELAY_SEND_REQUEST);
The leak occurs because you're starting a thread which has a reference to your context (fragment or activity). And until your thread is done - it won't be garbage collected.
That means, for example, if a user types something and you're waiting for a time to start requesting and meanwhile the user turns the phone and orientation change occurs - your activity/fragment will be recreated - but the old one (which started a thread and should be used when thread is done) is not gone and still present in memory.
Why are doing a request on the UI Thread? It blocks the UI, you know that right? I assume an AsyncTask may fit better.
What should you do?
Replace Timer with Handler and do the requests in a worker thread. Regarding the leak you have 2 options:
a) do nothing since the time for which your activity/fragment will be preserved is very small and it will be GCed after the request is done. (not recommended)
b) Utilize the AsyncTask and in the constructor of the AsyncTask pass the context (your listener) and store it as a weak reference object, like this:
private static class SomeWorkTask extends AsyncTask<Void,Void,Void>{
private WeakReference<ActionsListenerWithContext> weakListener;
public SomeWorkTask(ActionsListenerWithContext listener){
this.weakListener = new WeakReference<>(listener);
}
#Override
protected Void doInBackground(Void... voids) {
//do some work here
return null;
}
#Override
protected void onPostExecute(Void aVoid) {
if(weakListener.get() != null){
weakListener.get().callYourCallbacks();
}
}
}
and then you call it
new SomeWorkTask(listener).execute();
Utilizing WeakReference wrapper is a common and recommended practice.

Incremental search in android using Volley library?

I have somehow implemented incremental search in android using AsyncTask. In incremental search an API is called for each character entered in edit text to get suggestions from server. For example,
User types a -> API is called.
User types ab -> API is called.
User types abc -> API is called.
This makes three API calls for a, ab and abc respectively. If a user is still typing then all the previous requests (e.g. requests of a and ab) will be cancelled and the last request (abc) will be served only to avoid delays.
Now I want to implement this using Volley library for better performance. Could anybody help me how can I achieve this functionality using volley specially the mechanism of cancelling all the previous request and serve the last request only to get suggestions from server.
NOTE: I couldn't find regarding this that's why posting it here. Please do guide me because I am new to android and really in need of answer.

First you need to implement a TextWatcher to listen to change in edit text.
Depending on the requirement of the changed text, you cancel and add a request to queue.
private RequestQueue queue = VolleyUtils.getRequestQueue();
private static final String VOLLEY_TAG = "VT";
private EditText editText;
...
TextWatcher textChangedListener = new TextWatcher() {
#Override
public void afterTextChanged(Editable s) {}
#Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
#Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
if (s.length() != 0) {
// first cancel the current request with that tag
queue.cancelAll(VOLLEY_TAG);
// and then add a new one to queue
StringRequest stringRequest =
new StringRequest("http://blabla/servlet?param=" + s,
new Listener<String>() {
// request callbacks
};
stringRequest.setTag(VOLLEY_TAG);
queue.add(stringRequest);
}
}
};
editText.addTextChangedListener(textChangedListener);
Just remember that this design will gobble up bandwidth. A better way is to use Handler.post() to wait for several seconds before firing a request.

How can I make network calls very frequently

I have an auto complete feature which means every time the user types a letter, there is a network call to the server, the user can type very quickly and a lot
I usually use thirdparty libraries for network calls but this time they wouldn't work, I need to use AsyncTask by the looks of it.
I read that you can only execute an AsyncTask once. My question is, do I need to create an object of my AsyncTask everytime the user types a letter? is this the best approach?
I am aware of implementing Filterable in my adapter but I need to know about this without Filterable.

Instead of making network call when user type you can make a network call when user stops typing.
I was implement it for same case as yours.I have a AutocompleteextView and when user type i have to show him list of suggestions, but I call webservice when user stops typing.Below is my example -
private final static int DELAY_BEFOR_SEARCH = 2000;
Here is Autocomplete TextView Listener -
myAutocompleteTV.addTextChangedListener(new SearchListener ());
and here is Listener Class -
public class SearchListener implements TextWatcher{
#Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
}
#Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {
}
#Override
public void afterTextChanged(Editable s) {
try{
mMessageHandler.removeCallbacks(mSearchRunnable);
if(s.length()>0){
if(Utility.isNetworkAvailable(mContext)){
mMessageHandler.postDelayed(mSearchRunnable, DELAY_BEFOR_SEARCH);
}
else{
Toast.makeText(mContext, getResources().getString(R.string.no_network_message),Toast.LENGTH_SHORT).show();
}
}
}
catch (Exception e) {
e.printStackTrace();
}
}
}
and here is Runnable -
Runnable mSearchRunnable = new Runnable() {
public void run() {
//TODO call your webservice here
}
}
for example if user type want to search 'Android' and he types 'Andr' ans stops typing for 2000 ms then my network call execute.

App crashing after adding final modifier to Edit Text

I have an edit text i need to hook to textchanged event to to do a task.I had defined the overrdiimg for edittext first but after adding the text extraction code in the text chnaged event the IDE Flagged an error and auto corrected it by adding a final modifier in the line
like this
final EditText et1=(EditText)findViewById(R.id.editText1);
After chnaging the text the app crahses so i tried to retrive the edittext 2 times first for hooking to the event then for fetching the text,then also the app crashes.
The IDE had prompted me to add the final modifier in similar cases before but it had crashed the app so i had added the fetchbyID at the point where the object was needed
EditText et1=(EditText)findViewById(R.id.editText1);
et1.addTextChangedListener(new TextWatcher() {
#Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
new Thread(new Runnable() {
public void run() {
ImageView img=(ImageView)findViewById(R.id.imageView1);
EditText et=(EditText)findViewById(R.id.editText1);
img.setImageBitmap(thumbnail);
Bitmap b = workwithtext(thumbnail,et.getText().toString(),10);
img.setImageBitmap(b);
}
}).start();
}
#Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
#Override
public void afterTextChanged(Editable s) {
}
});
Please help me solve this issue

It crashes because you are trying to modify a UI component from a non UI thread.
new Thread(new Runnable() {
public void run() {
ImageView img=(ImageView)findViewById(R.id.imageView1);
//...
img.setImageBitmap(thumbnail);
//...
}
}).start();

Have the EditText et1 as a field in your class rather than a local variable.

You are updating ui from a background therad which is not possible. Also move your view intialization to onCreate.
img.setImageBitmap(b); // updating ui from thread not possible
Use runOnUiThread to update ui
runOnUiThread(new Runnable() {
public void run() {
// update ui here
}
});
Note you are starting a new thread everytime your onTextChanged is called which is not good. Also you initialize imageview and editext everytime in the threads run method which is not required.