Is there any way to use AsyncTask.execute() multiple times?
Im using AsyncTask to check, if User exist in my Room Database.
My Login.class looks like this:
public class Login extends AsyncTask<String, Boolean, Boolean> {
public Login(Context context, LoginListener listener){
db = ApplicationDatabase.getDatabase(context); //i get Room here
this.context = context; //context of app
this.listener = listener; //my interfece for observe Boolean, works ok
}
#Override
protected Boolean doInBackground(String... body){
try {
user = db.userDao().getUser(body[0], body[1]);
if (user != null)
return Boolean.TRUE; //we find user with credentials
else {
return Boolean.FALSE; //we not find user with that credentials (from body)
}
}
catch(Exception e){
return null;
}
}
protected void onPostExecute(Boolean result) {
listener.onLoginPerformed(result); //Boolen to activity
selfRestart(); //i want to restart task here
}
private void selfRestart(){
//maybe something to do here? its my own method
}
private ApplicationDatabase db;
private User user;
private LoginListener listener;
private Context context;
I call Task in this way (my Activity.class):
login = new Login(getApplicationContext(), this);
//this is an interface that i implements in Activity definition
loginButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
//execute() here, i cuted some not necesery code from here
try {
// im using get because i want to get valu from AsyncTask
login.execute(email, password).get();
}
catch(Exception e){ }
}
I Read, that we can reset AsyncTask by making new AsyncTask (Task = new Login()) StackOverflow Thread but it dont work for me. When i try to make something like this in my Login class:
private void selfRestart(){
Login task = new Login(context, listener);
task.execute("");
//im calling it in onPostExecute()
}
My android app crashes. My question is, what is the best way to reset AsyncTask that is implemented in diffrent file then my Activity class? Or maybe there is better way to make Login activity than implemented whole logic for login in AsyncTask?
EDIT:
Logcat:
2019-01-24 15:45:31.407 1048-1048/com.example.admin.keystroke_dynamics E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.admin.keystroke_dynamics, PID: 1048
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference
at com.example.admin.keystroke_dynamics.Activities.LoginActivity.onLoginPerformed(LoginActivity.java:62)
at com.example.admin.keystroke_dynamics.Login.onPostExecute(Login.java:38)
at com.example.admin.keystroke_dynamics.Login.onPostExecute(Login.java:14)
at android.os.AsyncTask.finish(AsyncTask.java:692)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:709)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:156)
at android.app.ActivityThread.main(ActivityThread.java:6523)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
You say,
I call Task in this way (my Activity.class):
login = new Login(getApplicationContext(), this);
//this is an interface that i implements in Activity definition
loginButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
//execute() here, i cuted some not necesery code from here
try {
// im using get because i want to get valu from AsyncTask
login.execute(email, password).get();
}
catch(Exception e){ }
}
, but no, you are not "calling" your task that way. You are creating a single instance of the task, and setting up an event handler that executes that task -- that specific instance -- whenever the loginButton is clicked. Since each AsyncTask instance may be executed only once, that will fail the second time the login button is clicked (if not sooner, for some other reason).
You also say,
I Read, that we can reset AsyncTask by making new AsyncTask (Task = new Login())
, but no, that does not reset anything, and indeed AsyncTask objects cannot be reset. The advice you read was to replace the used AsyncTask with a fresh instance. Instantiating a new AsyncTask has no particular effect on others. If you want to pursue that approach then it might look something like this:
loginButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v){
Login myLoginTask = login; // keep a reference to the current task
login = new Login(... arguments ...); // create a new task for the next click
try {
// use the original task
myLoginTask.execute(email, password).get();
}
catch(Exception e){ }
}
That specific implementation requires login to be non-final, so probably an instance variable of the containing class, not a local variable of the method from which your code was excerpted.
HOWEVER, your best way forward might very well be to ditch AsyncTask altogether. When you use it like this:
login.execute(email, password).get();
... you defeat the entire purpose. You are making the thread in which that runs block until the task completes (that's what AsyncTask::get is for), so the task is effectively synchronous. If that's what you require then you should just do the wanted work more directly instead of wrapping it up in an AsyncTask.
Related
I am using ActivityScenarioRule for Espresso UI Testing and I wanted to get access to the method getStringArray(), calling which requires the Activity . So, is there any way to retrieve the Activity by the ActivityScenarioRule , maybe something similar to getActivity in ActivityTestRule.
#Rule
public ActivityScenarioRule activityScenarioRule = new ActivityScenarioRule<>(MainActivity.class);
I am not using ActivityTestRule, because it is deprecated!
Since it appears you're using Java, here's how you'd do it:
#Rule
ActivityScenarioRule<MainActivity> activityScenarioRule = new ActivityScenarioRule<>(MainActivity.class);
#Test
public void test() {
activityScenarioRule.getScenario().onActivity(activity -> {
// use 'activity'.
});
}
Please read the documentation for more info on these new ways of interacting with the activity under test.
For anyone who wants Activity, but that without need to re-write all tests to run on UI-thread, a fairly straightforward Java way to get it:
Waiting for UI
Assume you want to test if a dialog is shown after some delay, the onActivity(...) hook runs on UI-thread, which means waiting in there would cause the dialog to be nerver shown.
In such cases you need to keep a strong-reference to ActivityScenario (as that prevents Activity close).
Test should wait for onActivity(...) hook to be called, then keep passed Activity's reference.
Finally, move test logic out of onActivity(...) hook.
Example
private ActivityScenario mActivityScenario;
#After
public void tearDown() throws Exception {
if (mActivityScenario != null) {
mActivityScenario.close();
}
mActivityScenario = null;
}
#Override
public Activity getActivity() {
if (mActivityScenario == null) {
mActivityScenario = ActivityScenario.launch(getActivityClassForScenario());
}
return tryAcquireScenarioActivity(mActivityScenario);
}
protected static Activity tryAcquireScenarioActivity(ActivityScenario activityScenario) {
Semaphore activityResource = new Semaphore(0);
Activity[] scenarioActivity = new Activity[1];
activityScenario.onActivity(activity -> {
scenarioActivity[0] = activity;
activityResource.release();
});
try {
activityResource.tryAcquire(15000, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
Assert.fail("Failed to acquire activity scenario semaphore");
}
Assert.assertNotNull("Scenario Activity should be non-null", scenarioActivity[0]);
return scenarioActivity[0];
}
Espresso states the following:
At the same time, the framework prevents direct access to activities
and views of the application because holding on to these objects and
operating on them off the UI thread is a major source of test
flakiness.
When there is no other way I use the following method to get an arbitrary activity from an ActivityScenarioRule. It uses onActivity mentioned in the accepted answer:
private <T extends Activity> T getActivity(ActivityScenarioRule<T> activityScenarioRule) {
AtomicReference<T> activityRef = new AtomicReference<>();
activityScenarioRule.getScenario().onActivity(activityRef::set);
return activityRef.get();
}
Any onView(...) code inside onActivity led to a timeout in my testcases. So, I extracted the activity and used it with success outside the onActivity. Beware tho! See the statement above.
#Test
fun checkForUpdate() {
val scenario = ActivityScenario.launch(MainActivity::class.java)
scenario.onActivity {
UpdateTool.checkForUpdate(it)
}
}
Im trying to implement MVVM architecture using ViewModel and LiveData. These two methods are inside a Activity:
private void handleResult(BoardViewModel vm) {
vm.getLiveDataSingleObj("Result").observe(this, new Observer<Object>() {
#Override
public void onChanged(#Nullable Object resultObj) {
Result result = (Result) resultObj;
if (!result.isCompleted()) return;
gotoResult();
}
});
}
And
private void gotoResult() {
Log.w(LOG_TAG, "Result: Moving to next activity");
Intent intent = new Intent(boardActivity, ResultActivity.class);
intent.putExtra("LEVEL", levelIndex);
intent.putExtra("MAP", mapIndex);
startActivity(intent);
}
The handleResult method is setup to listen for result objects that indicate that the game has ended and it is time to move on to the next activity ("gotoResult"). However, this completely breaks the navigation of the app, when i go back and then say attempt to start a new game session i instead instantly go to the next activity telling me I've already won.
Any ideas as to why it fires multiple times and eventually stops, letting me start a new session. To clarify, if I remove the gotoResult the logic works every single time no errors with indexes out of bounds or what have you, it's only when I add the goto that everything breaks.
ViewModel:
private void setupHashTypes() {
hashLiveData.put(KEY_BOARD, liveDataBoardQuery);
hashLiveData.put(KEY_STEPS_COUNTER, game.getStepsTakenLiveData());
hashLiveData.put(KEY_PATH_CHANGE, game.getPathChangedLiveData());
hashLiveData.put(KEY_VALUE_CHANGE, game.getValueChangeLiveData());
hashLiveData.put(KEY_TIMER, game.getTimerLiveData());
hashLiveData.put(KEY_SELECTED, game.getSelectedLiveData());
hashLiveData.put(KEY_DESELECTED, game.getDeselectedLiveData());
hashLiveData.put(KEY_HOLD, game.getHoldLiveData());
hashLiveData.put(KEY_UNHOLD, game.getUnholdLiveData());
hashLiveData.put(KEY_RESULT, game.getResultLiveData());
}
public LiveData<Object> getLiveDataSingleObj(String type) {
if (hashLiveData.containsKey(type)) {
return (LiveData<Object>) hashLiveData.get(type);
}
throw new IllegalArgumentException("Invalid: key was not found: " + type);
}
And the Model has getters, example:
private final SingleLiveEvent<Result> resultLiveData = new SingleLiveEvent<>();
public LiveData<Result> getResultLiveData() {
return resultLiveData;
}
you should remove the observer in onDestroy() method
Changing from MutableLiveData which always resends the previous set values to new subscribers, to SingleLiveEvent which doesn't have this behaviour, solved the problem.
The class can be found here: https://github.com/googlesamples/android-architecture/tree/dev-todo-mvvm-live/todoapp/app/src/main/java/com/example/android/architecture/blueprints/todoapp
I have this piece of code that runs alright when I put it in Eclipse, but for some reason it does not want to execute when I put it in an activity's onCreate method in Android studio.
Here is the code:
public class ItemListView extends AppCompatActivity{
String itemURL;
int listSize;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_item_list_view);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
Bundle itemData = getIntent().getExtras();
if(itemData==null){
return;
}
//Gets URL from search bar
itemURL = itemData.getString("itemURL");
try {
Document doc = Jsoup.connect("https://www.amazon.com/s/ref=nb_sb_ss_c_1_6?url=search-alias%3Daps&field-keywords=rx+390&sprefix=rx+390%2Caps%2C166&crid=2MTUBA4KGNY06").get();
String link = doc.select("h2#s-result-count").first().text();
System.out.println(link);
System.out.println(link.substring(1));
if (link.substring(1, 2).equals("-")) {
System.out.println("run1");
listSize = Integer.parseInt(link.substring(2, 3));
System.out.println(listSize);
try {
listSize = Integer.parseInt(link.substring(2, 4));
System.out.println(listSize);
} catch (Exception e) {
}
} else {
System.out.println("run2");
listSize = Integer.parseInt(link.substring(0, 1));
System.out.println(listSize);
try {
listSize = Integer.parseInt(link.substring(0, 2));
System.out.println(listSize);
} catch (Exception e) {
}
}
} catch (Exception e) {
}
System.out.println("listSize: " +listSize);
...
}
}
I need listSize to create a variable array depending on the URL, but when I print the value to make sure it's working it always gives me 0. I have tried running the code in a separate Java Class with AsyncTask and it works, but by the time the code executes in onPostExecute, it's too late since the class above has already tried to initialize the array.
Any advice would be appreciated, thanks!
What you need is a callback to allow you to initialize variable onPostExecute:
interface OnCallCompleteCallBack {
void onCallComplete(int listSize);
}
In your AsyncTask do this:
public class MyTask extends AsyncTask < ... > {
// Maintain a ref to callback
OnCallCompleteCallBack callback;
MyTask(OnCallCompleteCallBack callback) {
this.callback = callback;
}
...
#Override
protected void onPostExecute(Void aVoid) {
if (callback != null) {
callback.onCallComplete(listSize);
}
}
}
Make your Activity implement OnCallCompleteCallBack and start the AsyncTask like this:
new MyTask(this).execute();
You can then use the value inside your activity's implementation of onCallComplete()
Before I answer, just a few observations:
Naming your activity ItemListView seems wrong (an Activity is not a View).
You should never perform networks calls on the UI thread.
If you want to log, you should use Log instead of System.out.println().
And now to the answer. You should execute the code that fetches the data in an AsyncTask (as you mentions it works). Once the data is fetched, you should update array and at that point update the UI in onPostExecute().
Android works pretty well using the MVC (Model-View–Controller) pattern and your problem is a classic case where you need to update the model using data from the server and update the views accordingly. The activity represents controller in this case.
Please go through the topic in android developer site Android Developer, Read the section "Introducing Network Operations on a Separate Thread" - To avoid creating an unresponsive UI, don't perform network operations on the UI thread. By default, Android 3.0 (API level 11) and higher requires you to perform network operations on a thread other than the main UI thread; if you don't, a NetworkOnMainThreadException is thrown.
Thanks Ashish
I have three java files in my Android project. Two are activities (MainActivity and GeoActivity) and one is a plain java file (PostHttp -> sends data to server via the HTTP POST)
I switch over to GeoActivity via a simple button on-click method. GeoActivity returns the co-ordinates of the current location in a TextView AND sends them to a remote server via the HTTP POST.
I have a Handler.class which executes sends the Post Message after a delay of 50s. Something like this below. The problem i have is that when i click the back button and switch over to MainActivity i can still see in LogCat the echoes receiving from the server that the data is still being sent. How can i stop that?
GeoActivity.class
public class GeoActivity extends Activity {
Location location;
private Handler mHandler = new Handler();
protected void onCreate(Bundle savedInstanceState) {
....
if(location != null){
mHandler.postDelayed(updateTask,0);
}
...
}
...
public Runnable updateTask = new Runnable(){
public void run(){
mlocListener.onLocationChanged(location);
//send coordinates with a delay of 50s
new PostHttp(getUDID(),latitude,longitude).execute();
mHandler.postDelayed(updateTask, 50000);
}
Try acting on the activity's life cycle.
For example:
#Override
protected void onStop() {
super.onStop(); // Always call the superclass method first
// Save the note's current draft, because the activity is stopping
// and we want to be sure the current note progress isn't lost.
ContentValues values = new ContentValues();
values.put(NotePad.Notes.COLUMN_NAME_NOTE, getCurrentNoteText());
values.put(NotePad.Notes.COLUMN_NAME_TITLE, getCurrentNoteTitle());
getContentResolver().update(
mUri, // The URI for the note to update.
values, // The map of column names and new values to apply to them.
null, // No SELECT criteria are used.
null // No WHERE columns are used.
);
}
This doesn't destroy the activity, it will reside in memory. However, you can always resume when needed.
Source:
Stopping and Restarting Android Activities
my goal is to insert to a certain db 2 values, id and pass.
I have a registeration page which asks for that data and a button to complete the action.
So on the button listener what should I do?many told me to use AsyncTask (which I don't know to use) instead of Thread.
Remember that this class needs to get 2 parameters id and pass .. and as far as I know threads starts after using the start() method which invoke the run method, and the run method has no parameters.. so how can I pass those 2 parameters?
Anyway I'm very confused.
Another thing is that if I get any kind of error on the catch block I will put the error on a certain string something like : String error = exceptionInstance.toString(); and then I can take see that string from the registeration page and print the error.
myThreadInstance.start();
textViewInstance.setText(myThreadInstance.getError());
It's some kind of a marathon.. I'M CONFUSED!!!!!!!
According to me use AsyncTask instead of an Thread because it's easy to use and you have better control on Background thread without doing extra code for creating separate logic for updating Ui when Thread execution complete, calculate progress units to so user how much time take by an operation to done etc
Your First question how you send username and password to AsyncTask on button click .for this use AsyncTask Constructor as:
LoginOperation loginopertion=new LoginOperation(strusername, strpassword);
loginopertion.execute("");
Your Second answer how we receive username and password in AsyncTask and update Ui when Task complete for this use onPostExecute of AsyncTask to update Ui when doInBackground execution complete for example :
public class LoginOperation extends AsyncTask<String, Void, String> {
String strusername,strpassword;
public LoginOperation(String strusername, String strpassword){
this.strusername=strusername;
this.strpassword=strpassword;
}
#Override
protected void onPreExecute() {
//show progressbar here
}
#Override
protected String doInBackground(String... params) {
string result="";
try
{
result=="success or fail";
//do your network opertion here
}
catch(SQLException e)
{
result="ERROR";
}
return result;
}
#Override
protected void onPostExecute(String resultmsg) {
// show error here and update UI
//or other opertion if login success
textViewInstance.setText(resultmsg);
}
}
For more information about AsyncTask method's see
http://developer.android.com/reference/android/os/AsyncTask.html