Develop Reference

How to disable On Click Listener created in onCreate, in onPause? (In Android Studio)

In Android Studio, I am trying to open the second activity when corresponding button is pressed.However, I cannot reach that listener that I create in "onCreate" from onPause. I am following an approach like this:
public class MainActivity extends Activity {
private View.OnClickListener openSecondPage = new View.OnClickListener() {
#Override
public void onClick(View v) {
Button button_newPage = findViewById(R.id.button_newpage);
button_newPage.setText("Clicked");
Intent secondPage = new Intent(getApplicationContext(), SecondActivity.class );
startActivity(secondPage);
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button_newPage = findViewById(R.id.button_newpage);
button_newPage.setOnClickListener(openSecondPage);
}
public void onPause(){
super.onPause();
Button button_newPage = findViewById(R.id.button_newpage);
//Destroy the on click listener
button_newPage.setOnClickListener(null);
}
}
Also user will be able to come back to main activity and then go back to the second activity again. In that case I don't want to open a new activity. Instead I want to open previously created activity. For that case should I create a onResume() method and in that, call startActivity(secondPage). But in that case, since the secondPage is declared in onStart I won't be able to use in onResume. How can I handle that situation?
So there are actually 2 questions.. sorry about that, I didn't want to open 2 different questions for it.

Put Button button_newPage = findViewById(R.id.button_newpage); and button_newPage.setOnClickListener(openSecondPage); inside onResume instead of onCreate, like so:
#Override
protected void onResume() {
super.onResume();
Button button_newPage = findViewById(R.id.button_newpage);
button_newPage.setOnClickListener(openSecondPage);
}
That should solve at least part of your problem.

infinite while loop, while AsyncTask is not finish

I have a SplashScreen Activity which call Asynctask Class to get information in internet.
I want to wait while my Asynctask is not finish (time during on internet speed connection)
My activity:
public static boolean test = true;
[...]
final Liste en_ce_moment = new Liste("En ce moment au cinéma", nowMovie);
mesListes.add(en_ce_moment);
//call my Asynctask file
fetchNowMovie process = new fetchNowMovie();
process.execute();
while(test)
{
}
Intent i = new Intent(SplashScreenActivity.this, MainActivity.class);
startActivity(i);
My Asynctask:
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
SplashScreenActivity.test = false;
SplashScreenActivity.nowMovie.clear();
SplashScreenActivity.nowMovie.addAll(list);
}
Logically, the boolean became false in onPostExecute so the while loop stop and the intent have to start but the while loop never stop...

Let's do what you want to do in a safe way by using simple interface logic:
So we added our simple interface and we re-define your MyAsnycTask class's constructor like so:
public class MyAsnycTask extends AsyncTask
{
OnTaskFinished listener;
// Our simple interface
public interface OnTaskFinished {
void TimeToNextActivity();
}
// Your MyAsnycTask class constructor
public MyAsnycTask(OnTaskFinished l) {
listener = l;
}
. . .
As a last line of code in onPostExecute(), we're done whatever we're doing. So tell this via our listener:
listener.TimeToNextActivity();
To use our interface that we added earlier, your Activity must implements it. So we implements it. And in implemented method, we go to next Activity with Intent:
public class MyActivity extends Activity
implements MyAsnycTask.OnTaskFinished
{
#Override
public void TimeToNextActivity()
{
// Here go to next activity
Intent i = new Intent(this, MainActivity.class);
startActivity(i);
}
As we modified our MyAsnycTask class's constructor, we must initialize it like this:
MyAsnycTask process = new MyAsnycTask(this);
process.execute();

This looks like a problem hiding inside another problem, but to get through the first-level issue you could try using CountDownLatch instead of a static boolean:
CountDownLatch latch = new CountDownLatch(1);
fetchNowMovie process = new fetchNowMovie(latch);
process.execute();
latch.await();
Intent i = new Intent(SplashScreenActivity.this, MainActivity.class);
startActivity(i);
You'll have to accept the latch as part of your AsyncTask's constructor:
private final CountDownLatch latch;
public fetchNowMovie(CountDownLatch latch) {
this.latch = latch;
}
// ...
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
latch.countDown();
SplashScreenActivity.nowMovie.clear();
SplashScreenActivity.nowMovie.addAll(list);
}

Try to use very simple library:
https://github.com/Arasthel/AsyncJobLibrary
Just start your Splash activity:
Intent i = new Intent(context, SplashScreenActivity.class);
startActivity(i);
In "onCreate" method of Splash activity do, what you need in background and after mission complete, do on main thread (update list):
AsyncJob.doInBackground(new AsyncJob.OnBackgroundJob() {
#Override
public void doOnBackground() {
//load from local DB or http-request:
List<Movie> movieList = fetchNowMovie();
//You can convert movieList to Json string, for example and save in SharedPreferences. Or you can use local DB for saving new movies.
// Send the result to the UI thread and show it
AsyncJob.doOnMainThread(new AsyncJob.OnMainThreadJob() {
#Override
public void doInUIThread() {
Intent i = new Intent(splashScreenContext, MainActivity.class);
startActivity(i);
//load movies from shared preferences or local Database in MainActivity (onCreate)
}
});
}
});
Connect library (build.gradle in app-project directory):
dependencies {
...
implementation 'com.arasthel:asyncjob-library:1.0.3'
...
}

Android exit whole program syntax

currently I'm working on Android development, now I'm facing a problem to exit the whole application that had launched.
I'v tried .finish(), but it doesn't show what I want.
I have 2 Activities, A and B. Activity A will forward to Activity B when button click. In activity B, when I click button "Exit" (that I created) with the listener to trigger .finish(), it just back to Activity A but not to close whole application (what I want is back to home screen directly and kill the background process as well).
How can I exit whole application wherever in the application? Thank you.
button.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v) {
//here to exit whole application not just backwards to previous activity
}
});

You write in Activity A after
startActivity(new Intent(A.this, B.class))
finish()
then you also write in Activity B finish() on button click listener. It should works.
public class A extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(A.this, B.class));
finish(); // you must write this also in A activity to close whole application
}
});
}
public class B extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_1);
Button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
finish();
}
});
}

EDIT: I assumed there are cases when the underlying activity either should or shouldn't be terminated on return. This will allow you to handle both cases.
Case A)
Activity A starts activity B, which starts activity C. You want to close all of them from activity C. If they're all in the same task (i.e. probably your case) you can close the whole task by calling
finishAffinity();
According to docs this is what happens:
Finish this activity as well as all activities immediately below it in the current task that have the same affinity. This is typically used when an application can be launched on to another task (such as from an ACTION_VIEW of a content type it understands) and the user has used the up navigation to switch out of the current task and in to its own task. In this case, if the user has navigated down into any other activities of the second application, all of those should be removed from the original task as part of the task switch.
Note that this finish does not allow you to deliver results to the previous activity, and an exception will be thrown if you are trying to do so.
See Activity.finishAffinity().
Case B)
Activity A starts activity B, which starts activity C. You want to close activities B and C from activity C.
This is how you start activity C from B expecting and handling a result:
public class ActivityB extends Activity {
private static final int RC_ACTIVITY_C = 1;
public static final int RESULT_FINISH = 1;
...
public void startActivityC() {
Intent intent = new Intent(this, ActivityC.class);
startActivityForResult(intent, RC_ACTIVITY_C);
}
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == RC_ACTIVITY_C && resultCode == RESULT_FINISH) {
finish();
}
}
}
This is how you let activity B it has to finish from activity C. At any point before finishing activity C call:
setResult(ActivityB.RESULT_FINISH);
See Activity.startActivityForResult(Intent, int) and Activity.setResult(int).

You can try System.exit(0). That should do the job.
EDIT: Take a look at this post for the difference between finish() and System.exit(). Difference between finish() and System.exit(0)

Go to an activity from anywhere

I am implementing a login system. The user needs to be redirected to the login activity from any previous activity if the token is no longer valid. I can go to the login activity with this
new Intent(CurrentActivity.this, NextActivity.class);
But this needs the current activity. I just want to go to the login activity no matter where I am. I cannot know where I am because this is inside an entirely different package.

you should probably register in the Application class to ActivityLifecycleCallbacks and if the user is not registered send them to the correct Activity.
just be sure to not endlessly send them from the login page to itself
EDIT:
adding some code and explanation.
In order to figure out if an Activity that shouldn't be alive is going through lifecycle events you'll need to implement some sort of a gate keeper. Previously it used to be some sort of static state that is kept in the Application class and holds the current activity and sometime even the stack of current activities.
This was far from a complete solution and had issues due to different tasks and even isolated procesies.
In API 14 Android introduced the Activity lifecycle callbacks which can be passed into the method registerActivityLifecycleCallbacks int the Application class.
What you want to do basically is the following:
class ThepooshApplication extends Application {
private static sIsRegistered = false;
public static setIsRegistered(boolean isRegistered) { sIsRegistered = isRegistered; }
public void onCreate() {
registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks(){
#Override
void onActivityCreated(Activity activity, Bundle savedInstanceState){
if (!sIsRegistered && !(activity instanceof LoginActivity)) {
Intent loginIntent = new Intent(this, LoginActivity.class);
loginIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(loginIntent);
}
}
#Override
void onActivityStarted(Activity activity) { /*empty method*/ }
#Override
void onActivityResumed(Activity activity) { /*empty method*/ }
#Override
void onActivityPaused(Activity activity) { /*empty method*/ }
#Override
void onActivityStopped(Activity activity) { /*empty method*/ }
#Override
void onActivitySaveInstanceState(Activity activity, Bundle outState) { /*empty method*/ }
#Override
void onActivityDestroyed(Activity activity) { /*empty method*/ }
});
}
}

You must add FLAG_ACTIVITY_NEW_TASK flag to your intent
myIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
Try some like this
Intent i = new Intent();
i.setClass(this,TestActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);
Replace TestActivity.class for your target activity

How can I access a method from an activity and use it into another activity in Android?

I have the first class named iHave
public class iHave extends ActionBarActivity
{
//below is the instance for calling the method from the other activity.
(The name of the other activity is **iThank**)
**iThank thankYou = new iThank();**
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_i_have);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
**//this is the method I want to access from iThank class** **strong text**
thankYou.display();
}
});
}
//The Next class is "iThank"
public class iThank extends ActionBarActivity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_i_thank);
txtThank = (TextView) findViewById(R.id.textView3);
//this is the method I want to access/use from iHave Activity
public void display()
{
txtThank.setText ("Shine");
}
}
How can I use the method "public void display()" of iThank activity to the "iHave" activity? It always gives me an error of NullPointerException. Please help. Thank you very much!

How can I access a method from an activity and use it into another
activity in Android?
By creating object for other to access method from Activity is right way.
Use LocalBroadcastManager for communicating between application components.
1. Send broadcast from iHave on Button click:
#Override
public void onClick(View v)
{
Intent intent = new Intent("DISPLAY_EVENT");
LocalBroadcastManager.getInstance(v.getContext()).sendBroadcast(intent);
}
2. Register LocalBroadcastManager in iThank Activity:
#Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
LocalBroadcastManager.getInstance(this).registerReceiver(ReceiveMessage,
new IntentFilter("DISPLAY_EVENT"));
}
3. Create BroadcastReceiver object and call display() method in iThank Activity:
private BroadcastReceiver ReceiveMessage = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
display();
}
};
Also add null check in display method for TextView:
public void display()
{
if(txtThank !=null)
txtThank.setText ("Shine");
}

Please don't to this, it is not how activities are intended to work. You might want to have a look over the Activities Developer Guide to get started. If you want to launch a new activity (e.g. iThank) from the current foreground activity (e.g. iHave), you never instantiate the class yourself directly and always launch it using an intent. If you have data to pass along (such as a message to display), it needs to be bundled along with the intent as an extra (see same link).
Activities should never call methods on each other directly, because this requires them to have references to each other. The framework manages the life cycle of each activity independently, and those references can lead to leaks.