currently trying to create the front-end for my Convolutional neural network image classifier.
what i'm trying to build is an app which sends a continuous stream of images to my server for classification, the total stream classification will be averaged and viewed for the user.
the reason i want this specific trait is because classifying many images of the same 3D object could improve accuracy.
building the app on camera2 demo from github, i wasn't able to google a solution.
i have tried creating a Asynctask which will rerun the takePhoto() method at onPostExecute but canceling the task is close to impossible, without talking about rerunning the task which doesnt allow me to cancel because i'm not saving the task as a variable.
also, each time i take a picture the device stutters a bit, is this unavoidable using camera2?
i have thought about moving to the older camera api, camera2 is a complete pain in the a**.
any new idea would be lovely at this point.
would apreciate if anyone who was able to stream images easily using camera2 or the older ap could post an example or help me with the issue.
this is my asynctask if this actualy could work and im just doing it wrong:
public class AsyncTakePicture extends AsyncTask<Void, Void, Void> {
private boolean running = true;
#Override
protected void onCancelled() {
running = false;
}
#Override
protected Void doInBackground(Void... params) {
while (running) {
takePicture();
try {
// no need for alot of images, so one image per 2 seconds is good
Thread.sleep(2000);
} catch (Exception e) {
running = false;
}
}
return null;
}
protected void onPostExecute(Void result) {
if (running){
myAsyncTask.execute();
} else {
Log.i("AsyncTask:"," done");
}
}
}
the idea is that once the task is called, it will rerun and take more photos until cancelled. Async is called because i don't want the UI to lag. thing is, to repeat the task i cannot initiate it as a variable, and if i cannot initiate then i cannot use cancel(boolean).
Related
I am trying to make an android app that captures photos after every 5 seconds. Currently the technique i'm using, uses the phone's camera app to capture the photo. It requires the user to capture the photo and then to press ok and only after that the control returns back to the android app. I found some codes to do the same without human interaction, but since i'm new to android, i'm not able to understand codes them because most of them are incomplete and divided into multiple activities. Can this be done using just one activity?
EDIT :
The codes mentioned above can be found here
I suggest to you to use this library (here documentation) instead the official Camera Api of Android that could be really tricky to use for beginners
Then your code could be like this
private final Handler handler = new Handler(); //This should be declared before OnCreate
private Runnable photoRunnable; //This also
CameraView camera = findViewById(R.id.camera);
camera.addCameraListener(new CameraListener() {
public void onPictureTaken(PictureResult result) {
//Handle result here!
}
});
photoRunnable = new Runnable() {
#Override
public void run() {
try {
camera.takePicture(); //The result will be in onPictureTaken
}
catch (Exception e) {
e.printStackTrace();
//Handle Exception!
}
finally{
//also call the same runnable to call it at regular interval
handler.postDelayed(this, 10*1000); //10*1000 is your interval (in this case 10 seconds)
}
}
};
//runnable must be execute once
handler.post(photoRunnable);
Remember to manage the lifecycle of handler
I have created an AsyncTsak class in my project which downloads some information from web server. I am sure that it works well because when it is called by onCreate() , I can see the result . But unfortunately when I call it again via a button it doesn't work.
I am not sure but i think i have read somewhere about this problem . It said , we are permitted to use AsyncTask class only once.
AsyncTask class
class DownloadAdvertismentLevel2 extends AsyncTask<String,String,String>{
String [] ImageInformation=null;
protected void onPreExecute(){
// do nothing !
}
protected String doInBackground(String...Urls){
String Data="";
HttpURLConnection urlConnection = null;
try{
URL myUrl=new URL("http://10.0.2.2:80/Urgence/ads.aspx?Action=DownloadIds&TB="+TopBoundry+"&LB="+LowBoundry);
urlConnection = (HttpURLConnection)myUrl.openConnection();
BufferedReader in = new BufferedReader (new InputStreamReader(urlConnection.getInputStream()));
String temp="";
// Data is used to store Server's Response
while((temp=in.readLine())!=null)
{
Data=Data+temp;
}
}
catch(Exception ex){
Log.d("Er>doInBackground", ex.toString());
urlConnection.disconnect();
}
finally{
urlConnection.disconnect();
}
return Data;// it sends Result to onPostExcute
}
protected void onPostExecute(String Data){
createPhotoAlbum();
pb.closedProg();
}
}
onCreate
Here I don't have any problem . It works fine
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.ads);
new DownloadAdvertismentLevel2().execute();
}
Via Button
ButtonSeeMore.setOnClickListener(new View.OnClickListener(){
public void onClick(View view) {
Counting();
}});
Counting
public void Counting(){
if(TotalRows-6>0){
TopBoundry=TotalRows;
LowBoundry=TotalRows-6;
TotalRows=LowBoundry;
}
new DownloadAdvertismentLevel2().execute();
}
Please consider that I need to use this class till it shows the information. What would you suggest ?
To expand on what JVN said about AsyncTask
Each instance of Async task can only be executed once.
The task can be executed only once (an exception will be thrown if a second execution is attempted.)
http://developer.android.com/reference/android/os/AsyncTask.html (Under 'Threading Rules')
This doesn't stop you making a new instance -
public void Counting(){
if(TotalRows-6>0){
TopBoundry=TotalRows;
LowBoundry=TotalRows-6;
TotalRows=LowBoundry;
}
new DownloadAdvertismentLevel2().execute();
new DownloadAdvertismentLevel2().execute();
}
^ The code above will run your task twice.
Your code looks fine.
I would guess that the problem is (in order of likelihood)
1) On click isn't working
2) Post Execute isn't working as expected
3) The server response isn't being read correctly
4) Your Server isn't handling the request properly
But this would be obvious if you run your debugger or add some extra log outputs
1) I think you might be able to use the Async task only once in the class. But definitely it can be called multiple times.
2) please check if your button onclicklistener() function is really getting called on button click. try some logs in that.
because the code seems to be fine.
To allow multiple asycnh tasks run at the same time you need to use the 'executeOnExceuter mechanism:
See this note from the Android doucmentation:
When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. Starting with HONEYCOMB, tasks are executed on a single thread to avoid common application errors caused by parallel execution.
If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.
An example invocation would look like (this particular example is from a video manipulation app - the 'distributionTask' is an instance of a class that extends AsynchTask):
//Now execute synch task - to allow multiple AsynchTasks execute in parallel the
//'executeOnExecutor' call is required. It needs to be used with caution to avoid the usual synchronization issues and also
//to avoid too many threads being created
distributionTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, Environment.getExternalStorageDirectory() + "/videoChunk_"+i+".mp4");
I have a download activity which downloads some zip files for my application.
I want my activity have this features :
capable of pause/resume download
shows download progress in my activity's UI by a progress bar ( not with
dialogProgress)
shows notification with download progress and when user clicks on the
notification it opens my activity even when the app is closed and my UI keeps updated during download
I have searched a lot and saw lots of methods that can be used to download files (like using AsyncTask/Downloadmanager/Groundy ... ) but I don't know which one of them has the features I want
what do you think is the best way to achieve this features all together ??
I don't want the full code from you, just some tips and methods or references to help me implement each of these features and find the best way.
Thanks for your time.
Fundamentally you can use AsyncTask through which you would be able to achieve the above, if the download is strictly tied to the activity. However AsyncTask needs to be properly cancelled once user cancel or back out from activity. Also it provide basic mechanism to do the progress thing.
For example, imagine a simple async task (not the best implementation) but something like below
class SearchAsyncTask extends AsyncTask<String, Void, Void> {
SearchHttpClient searchHttpClient = null;
public SearchAsyncTask(SearchHttpClient client) {
searchHttpClient = client;
}
#Override
protected void onProgressUpdate(Void... values) {
// You can update the progress on dialog here
super.onProgressUpdate(values);
}
#Override
protected void onCancelled() {
// Cancel the http downloading here
super.onCancelled();
}
protected Void doInBackground(String... params) {
try {
// Perform http operation here
// publish progress using method publishProgress(values)
return null;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute() {
// If not cancelled then do UI work
}
}
Now in your activity's onDestroy method
#Override
protected void onDestroy() {
Log.d(TAG, "ResultListActivity onDestory called");
if (mSearchTask != null && mSearchTask.getStatus() != AsyncTask.Status.FINISHED) {
// This would not cancel downloading from httpClient
// we have do handle that manually in onCancelled event inside AsyncTask
mSearchTask.cancel(true);
mSearchTask = null;
}
super.onDestroy();
}
However if you allow user to Download file even independent of activity (like it continues downloading even if user got away from Activity), I would suggest to use a Service which can do the stuff in background.
UPDATE: Just noticed there is a similar answer on Stackoverflow which explains my thoughts in further detail Download a file with Android, and showing the progress in a ProgressDialog
I am developing an Android application and when it launches :
1) I make an HTTP Request to my server to send a small JSON file.
2) Open a webView to show a URL.
When the server is running properly there is absolutely no problem and everything goes smoothly.
HOWEVER , if for any reason the server is down , the HTTP request literally hangs and i need to wait till there is an HTTP timeOut which is around 30seconds till i actually see the webView with the URL loading.
I read that i shouldn't make any networking inside the UI thread and i should use another thread for that.
In BlackBerry , that i have already developed the application for , this is as simple as that :
new Thread(){
public void run(){
HttpConnection hc =
(HttpConnection)Connector.open("http://www.stackoverflow.com");
}
}.start();
I just start a new thread and inside i make the requests and all the necessary networking. That way , even when my server is not reachable the webView is loaded immediately without making the user wait and sense that the app is actually hanging.
How could i do exactly the same in Android , easiest way possible ?
Why not to use the same method as you use it for BlackBerry?
new Thread() {
public void run() {
new URL("http://www.stackoverflow.com").getContent();
}
}.start();
Use AsyncTask, it's the simplest way to do that. For more details:
http://developer.android.com/reference/android/os/AsyncTask.html
In icecream sandwich and above you are not allowed to use any web cal in UI thread. However you may use threads, but best way proposed by android is to use Async task. A very simple example is as follow.
"AsyncTask < Parameters Type, Progress Value Type, Return Type >"
class MyAsyncTask extends AsyncTask<String, String, String> {
#Override
protected void onPreExecute() {
// Runs on UI thread- Any code you wants
// to execute before web service call. Put it here.
// Eg show progress dialog
}
#Override
protected String doInBackground(String... params) {
// Runs in background thread
String result = //your web service request;
return result;
}
#Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);
}
#Override
protected void onPostExecute(String resp) {
// runs in UI thread - You may do what you want with response
// Eg Cancel progress dialog - Use result
}
}
I think this is a quite common problem, but still I didn't find a satisfactory answer so I'm going to ask myself.
This is a piece of code:
// this is insine OnClickView
TextView status = (TextView) findViewById(R.id.status);
status.setText("Trying to connect to the server...");
try {
// this opens a socket and send a login request to the server.
int result = CommunicationManager.login(String email, String password);
switch (result) {
case CommunicationManager.SUCCESS:
// login ok, go on with next screen
break;
case CommunicationManager.WRONG_EMAIL:
status.setTextColor(Color.RED);
status.setText("Wrong Email!");
break;
case CommunicationManager.WRONG_PASSWORD:
status.setTextColor(Color.RED);
status.setText("Wrong Password!");
break;
}
} catch (CommunicationException e) {
status.setTextColor(Color.RED);
status.setText("Unable to estabilish a connection!");
} catch (ProtocolException e) {
status.setTextColor(Color.RED);
status.setText("Protocol error!");
}
This is what I would like to achieve:
User click Send button;
status textview shows "Trying to connect to the server...";
UI "waits" for communications to be over;
status textview shows result accordingly.
But instead when user clicks Send button, UI freezes (oddly before status text appears) until communication is done (I tried to connect to an unknown host).
A quick fix is to set a socket timeout, but I don't like this kind of solution: UI still freezes and which timeout should be set?
My first thought were Thread obviously, but as you can see I need to return a value, thing that in threading environment doesn't make much sense since threads run independently and asynchronously.
So what I need is definitely that UI waits for the service to be executed but without freezing.
By the way it seems to me that waiting for a return value means that UI has to wait for the task to be over, I just would not let it freeze.
I came across AsyncTask but I see two major disadvantages:
it seems to me that is too tightly coupled with UI;
what if I want to execute service with Integer, String and Boolean parameters? Should I extend AsyncTask<Object, Void, Void>?
Both leads to inextensibility.
What can I do to achieve my goal?
Please note that another request to the service will be a request for something that could not be ready yet, so I should automatically repeat request every few time (let's say ten minutes). So probably I'll need something I can use with TimerTask, but I'll still need to return a value to UI every time I execute that service (so I can update the status text and let the user know what's going on).
This is typical use case while dealing through external communication i.e. HTTP calls.
Best way is to use AsyncTask. To give you answers for your concerns for AsyncTask.
it seems to me that is too tightly coupled with UI;
Here good code design will play a role. You can write you own call back mechanism to get rid of tight coupling. Example can be below.
Create your version for request and response you need for WS call. It can be very simple primitive type or complex type parameters.
class Result{
//Define more para.
}
class Request{
//Deinf more para.
}
Write below callback interface.
public interface MyCallBack {
public void onComplete(Result result);}
Create AsyncTask and get above Interface object in constructor, same object can return Result object.
class LongRunningTask extends AsyncTask<Request, Integer, Long>{
private MyCallBack callback;
public LongRunningTask(MyCallBack callback) {
super();
this.callback = callback;
}
#Override
protected Long doInBackground(Request... params) {
// Perform your back ground task.
return null;
}
#Override
protected void onPostExecute(Long result) {
super.onPostExecute(result);
callback.onComplete(new Result()); //Here result is dummy but in real it should be contructred from doInBackground() method
}
}
Now last and important part to implement the interface and call asynctask. I am trying to reuse your code to have better clarity.
public class MainActivity extends Activity implements MyCallBack{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView status = (TextView) findViewById(R.id.status);
status.setText("Trying to connect to the server...");
}
private void onClick(){
//Similer to CommunicationManager.login(String email, String password); in your code.
LongRunningTask longRunningTask = new LongRunningTask(this);
longRunningTask.execute(new Request());
}
#Override
public void onComplete(Result result) {
try {
int result = result.getStatus
switch (result) {
case CommunicationManager.SUCCESS:
// login ok, go on with next screen
break;
case CommunicationManager.WRONG_EMAIL:
status.setTextColor(Color.RED);
status.setText("Wrong Email!");
break;
case CommunicationManager.WRONG_PASSWORD:
status.setTextColor(Color.RED);
status.setText("Wrong Password!");
break;
}
} catch (CommunicationException e) {
status.setTextColor(Color.RED);
status.setText("Unable to estabilish a connection!");
} catch (ProtocolException e) {
status.setTextColor(Color.RED);
status.setText("Protocol error!");
}
}
what if I want to execute service with Integer, String and Boolean parameters? Should I extend AsyncTask?
First Parameter is any user defined para. In case you need to pass multiple parameters then put them in to form of entity (i.e. - Class). Also, you can pass initial configuration parameter in constructor of AsyncTask i.e. - Communication URL.
Hope it will help.
Use multi threading, do all the communication in a different thread
Use worker thread, or AsyncTask for doing long-running operations.
Moreover, from Android Honeycomb, system throws exception, if you perform network operations on UI thread.