in my app in android, i need change background image in image view on 10 seconds once. so that i call a Async Task within a run method. when I execute the app it crashes.
It gives the Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() Exception to me.
I know I have to use Thread, but I do not know how to do so properly. Please help me.
This is my code sample:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
.................
new Thread()
{
public void run()
{
while(true){
try
{
Thread.sleep(5000);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
count = count + 1;
new ImageChange().execute();
}
}
}.start();
} // OnCreate End
class ImageChange extends AsyncTask<Void, Void, Void>
{
protected void onPreExecute() {
}
protected void onPostExecute(Void unused) {
iv1.setImageBitmap(b1);
iv2.setImageBitmap(b2);
}
protected Void doInBackground(Void... arg0) {
switch(count){
case 1:
b1 = BitmapFactory.decodeFile(f1.getAbsolutePath());
b2 = BitmapFactory.decodeFile(f2.getAbsolutePath());
break;
case 2:
b1 = BitmapFactory.decodeFile(f2.getAbsolutePath());
b2 = BitmapFactory.decodeFile(f1.getAbsolutePath());
break;
default :
count = 0;
b1 = BitmapFactory.decodeFile(f1.getAbsolutePath());
b2 = BitmapFactory.decodeFile(f2.getAbsolutePath());
break;
}
return null;
}
}
You're calling the AsyncTask from a worker Thread. This way it has no access to the UI thread. You probably should consider using a Handler.
Probably, the problem is that you must execute the ImageChange.doInBackground() method in the UI thread. Try to change your code like this:
class ImageChange extends AsyncTask<Void, Void, Void> {
Activity act;
public ImageChange(Activity act) {
this.act = act;
}
protected void onPostExecute(Void unused) {
iv1.setImageBitmap(b1);
iv2.setImageBitmap(b2);
}
protected Void doInBackground(Void... arg0) {
switch(count) {
case 1:
helperMethod(f1.getAbsolutePath(), f2.getAbsolutePath());
break;
case 2:
helperMethod(f2.getAbsolutePath(), f1.getAbsolutePath());
break;
default :
count = 0;
helperMethod(f1.getAbsolutePath(), f2.getAbsolutePath());
break;
}
return null;
}
private void helperMethod(String a, String b) {
act.runOnUIThread(new Runable() {
public void run() {
b1 = BitmapFactory.decodeFile(a);
b2 = BitmapFactory.decodeFile(b);
}
});
}
}
Note that you must pass an Activity to the ImageChange class constructor. It means that you have to call the asyncTask in this way:
new ImageChange(this).execute();
Also consider the possibility of using the class TimerTask
EDIT: Change the Activity part of your code with this:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
.................
new ImageChange().execute();
} // OnCreate End
And add the while(true) to the ImageChange class:
protected Void doInBackground(Void... arg0) {
while(true) {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
count = count + 1;
switch(count) {
...
}
}
return null;
}
EDIT2: You can solve the problem about onPostExecute inserting the code that must be execute after each iteration inside the while loop:
protected Void doInBackground(Void... arg0) {
while(true) {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
count = count + 1;
switch(count) {
...
}
act.runOnUIThread(new Runnable() {
public void run() {
iv1.setImageBitmap(b1);
iv2.setImageBitmap(b2);
}
});
}
return null;
}
The code you insert inside the while loop must run in the UI thread; in fact, every onPostExecute method of the AsyncTask class runs on UI thread.
i solved the problem by using Handler Thread.
Related
I'm facing a problem: I created two Activities.
One is the main Activity, which has a Button.
When I click this Button, the second Activity starts.
The second Activity uses an Asynctask in which a number is incremented from 1 to 10 and displays this number in a Textview
What I'm facing is that when I click the back Button while the Asynctask has not completed and then again go to the second Activity the Asynctask is not run from start immediately.
I know because in background when it completed the old task then it again starts a new task. Is there a way to fix this when destroying the Activity it also destroy the Asynctask?
Here is video sample for my problem.
Code for Main Activity:
public class MainActivity extends AppCompatActivity {
Button bt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bt = (Button) findViewById(R.id.bt);
bt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent i = new Intent(MainActivity.this,SecondAcitivity.class);
startActivity(i);
}
});
}
}
Code of Second Activity:
public class SecondAcitivity extends AppCompatActivity {
TextView t1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second_acitivity);
t1 = (TextView) findViewById(R.id.t1);
OurWork obj = new OurWork();
obj.execute();
}
class OurWork extends AsyncTask<Void, Integer, String> {
#Override
protected String doInBackground(Void... params) {
int i = 0;
while (i < 11) {
try {
Thread.sleep(700);
publishProgress(i);
i++;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return "Successfully Completed";
}
#Override
protected void onProgressUpdate(Integer... values) {
t1.setText(values[0] + "%");
}
#Override
protected void onPostExecute(String result) {
t1.setText(result);
}
}
}
you need to cancel the task on back pressed, and you need to monitor if the task is canceled while executing the doInbackground().
1- override onbackpressed:
#Override
public void onBackPressed() {
obj.cancel(true); // where obj is the asyncTask refernce object name
super.onBackPressed();
}
2- monitor isCanceled()
#Override
protected String doInBackground(Void... params) {
int i = 0;
while (i < 11 && !isCancelled()) { // added !isCancelled()
try {
Thread.sleep(700);
publishProgress(i);
i++;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return "Successfully Completed";
}
on next iteration of the while loop, after cancel(true); is called,the loop will quit, and doInBackground() will return.
When you press back button , onBackPressed callback is called. so you can basically try this :
#Override
public void onBackPressed() {
if (asyncFetch.getStatus() == AsyncTask.Status.RUNNING) {
asyncFetch.cancel(true);
}
finish();
}
Try to use :
private OurWork task;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second_acitivity);
t1 = (TextView) findViewById(R.id.t1);
task = new OurWork();
task.execute();
}
#Override
public void onBackPressed() {
task.cancel(true);
super.onBackPressed();
}
AsyncTask runs in background of the activity where it was hosted. If OnPause or OnDestroy is called, AsyncTask is destroyed, so to solve this issue, Override OnResume and execute AsyncTask again.
To cancel the asyncTask even when it is running when back is pressed, add this to onBackPressed:
public class SecondAcitivity extends AppCompatActivity {
TextView t1;
static OurWork obj;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second_acitivity);
t1 = (TextView) findViewById(R.id.t1);
obj = new OurWork();
obj.execute();
}
class OurWork extends AsyncTask<Void, Integer, String> {
#Override
protected String doInBackground(Void... params) {
int i = 0;
while (i < 11) {
try {
Thread.sleep(700);
publishProgress(i);
i++;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return "Successfully Completed";
}
#Override
protected void onProgressUpdate(Integer... values) {
t1.setText(values[0] + "%");
}
#Override
protected void onPostExecute(String result) {
t1.setText(result);
}
}
//override onBackPressed and do this
#Override
public void onBackPressed() {
if (obj!=null && (obj.getStatus()== AsyncTask.Status.RUNNING ||
obj.getStatus()== AsyncTask.Status.PENDING ))
obj.cancel(true);
super.onBackPressed();
}
}
I'm having some trouble with an AsyncTask subclass.
I have a main activity as below that displays a button and a number that counts up on the screen. Clicking the button launches an Edit activity where a number can be entered.
The number displayed on the Main activity should update with the timer which it does but the trouble I'm having is that I can't stop the timer. It should stop when entering the Edit activity and returning from it as well, as well as restart with the a new value too but it doesn't, the timer is always running with the first entered value, it never stops, even when I leave the program and return to the home screen.
I've looked at posts here such as Can't cancel Async task in android but they all just mention checking for isCancelled() which I'm doing. Can anyone see/explain why I can't stop this AsyncTask ?
public class MainActivity extends Activity {
#Override
UpdateTimer ut;
TextView tvn;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public void onResume() {
super.onResume();
tvn = (TextView) findViewById(R.id.numDisplay);
if(ut != null )//&& ut.getStatus() == AsyncTask.Status.RUNNING) {
ut.cancel(true);
ut.cancelled = true;
Log.d("-----M_r","called cancel: "+ut.isCancelled()+" "+cancelled);
}
if (updateRequired) {
ut = new UpdateTimer();
ut.execute(number);
updateRequired = false;
}
}
public void onEditButtonPressed(View caller) {
// kill any running timer
if(ut != null )
{
ut.cancel(true);
ut.cancelled = true;
}
// start the edit screen
Intent e_intent = new Intent(this, EditActivity.class);
startActivity(e_intent);
}
private void updateScreen(long number) {
// update screen with current values
tvn.setText("" + number);
}
private class UpdateTimer extends AsyncTask<Long, Long, Integer> {
long number;
public boolean cancelled;
#Override
protected Integer doInBackground(Long... params) {
number = params[0];
cancelled = false;
while(true) {
number += 1;
//sleep for 1 second
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// tell this AsyncTask to update the time on screen
publishProgress(number);
// check if timer needs to stop
if (isCancelled()) break;
if(cancelled) break;
}
return null;
}
protected void onProgressUpdate(Long... progress) {
Log.d("-----M_ut","updated: "+number+" "+this.isCancelled()+" "+cancelled);
updateScreen(progress[0]);
}
protected void onCancelled(Integer result) {
cancelled = true;
Log.d("-----M_ut","-- cancelled called: "+this.isCancelled());
}
}
protected void onStop()
{
super.onStop();
// kill any running timer
if(ut != null) {
ut.cancel(true);
}
}
}
Try this...
remove the variable..cancelled and change to this..
#Override
protected void onCancelled() {
super.onCancelled();
}
call the super.onCancelled instead..
And in the doInBackground check
if (isCancelled()) {
break;
}
Try calling from your activity ut.cancel(true);
Hope it works:)
private YourAsyncTask ut;
declare your asyncTask in your activity.
ut = new YourAsyncTask().execute();
instantiate it like this.
ut.cancel(true);
kill/cancel it like this.
i want to increment a progress dialog from a thread inside a service, i have really hard time doing that, this is my code please help me.
I tried many different ways including asyncTask (I had problem with context)
and tried with static functions but its not working properly,
I pretty new with android please explain me the problem here.
the activity
public class MainActivity extends Activity {
ProgressDialog progressBar;
private void showProgrssBar() {
progressBar.show();
}
private void dismissProgressBar() {
progressBar.dismiss();
}
private void increaseProgressBar(int total) {
progressBar.incrementProgressBy(total);
};
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
createProgressBarDialog();
Intent n = new Intent(this, myService.class);
startService(n);
}
private void createProgressBarDialog()
{
progressBar = new ProgressDialog(this);
progressBar.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressBar.setMax(200);
progressBar.setMessage("Recieving bluetooth data");
progressBar.setCanceledOnTouchOutside(false);
}
the service:
public class myService extends Service
{
private myThread myThread;
Handler handler = new Handler()
{
#Override
public void handleMessage(android.os.Message msg)
{
int total = msg.getData().getInt("total");
if (total == -1)
{
dismissProgressBar();
}
else if (total == 0)
{
showProgrssBar();
}
else
{
increaseProgressBar(total);
}
}
};
#Override
public int onStartCommand(Intent intent, int flags, int startId)
{
myThread = new myThread(handler);
myThread.start();
return START_STICKY;
}
the thread
class myThread extends Thread
{
Handler h;
int numOfLinesToRead = 220;
int line = 0;
public myThread(Handler h)
{
this.h = h;
}
private void increaseProgressBarOnActivity(int i_MsgType)
{
Message msg = h.obtainMessage();
Bundle b = new Bundle();
b.putInt("total", i_MsgType);
msg.setData(b);
h.sendMessage(msg);
}
#Override
public void run() {
super.run();
int increase;
try
{
Thread.sleep(1);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
for (; line < 220; line++)
{
increase = (line*100/numOfLinesToRead);
if (increase != 0)
{
increaseProgressBarOnActivity(increase);
try
{
Thread.sleep(90);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
}
}
}
Despite you having already tried AsyncTask, I still would strongly recommend to use it.
Just take a look at the onProgressUpdate() method. It is made to update the UI from AsyncTask.
Here is an example of how it could look like:
private class DownloadFilesTask extends AsyncTask<String, Integer, Long> {
private ProgressDialog progressBar;
#Override
protected void onPreExecute(){
super.onPreExecute();
progressBar= new ProgressDialog(getApplicationContext());
progressBar.setMessage("Loading...");
progressBar.show();
}
protected Long doInBackground(String... params) {
long someLong;
// do something here with params
// the Integer variable is used for progress
publishProgress(i);
// call it for example while downloading a file
return someLong;
}
// this is called whenever you call puhlishProgress(Integer)
protected void onProgressUpdate(Integer... progress) {
progressBar.incrementProgressBy(progress[0]);
}
// the onPostexecute method receives the return type of doInBackGround()
protected void onPostExecute(Long result) {
// do something with the result
progressBar.dismiss();
}
}
You said your problem was getting the Context. Well: Service is a Context
So you could simply make the AsyncTask an inner class of your Service and then use its Context.
I write a Splash Screeen to run at the boot time of application
public class SplashScreen extends Activity {
ImageView imgView;
int[] imgID = new int[]{R.drawable.frame0, R.drawable.frame1, R.drawable.frame2, R.drawable.frame3,
R.drawable.frame4, R.drawable.frame5, R.drawable.frame6};
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.splash);
imgView = (ImageView) findViewById(R.id.imgSplash);
new Thread(new WelcomeScreen()).start();
}
private class WelcomeScreen implements Runnable {
#Override
public void run() {
try {
for (int i = 0; i < imgID.length; i++)
{
imgView.setImageResource(imgID[i]);
sleep(500);
}
} catch (InterruptedException e) {
}finally {
Intent intent = new Intent(SplashScreen.this,LoginActivity.class);
startActivity(intent);
finish();
}
}
}
}
It getting error "Sorry the application has stopped unexpectedly" . I don't know why . Somebody can help me ????
you can not set the resource for yuor ImageView inside a thread different from the UI Thread.
you can use runOnUiThread. It takes as paramter a runnable, and post it in the UI Thread queue. There, the UI thead takes it and update your ImageView. All in all your runnable will become:
private class WelcomeScreen implements Runnable {
#Override
public void run() {
try {
for (int i = 0; i < imgID.length; i++)
{
final int resuorceId = imgID[i];
runOnUiThread(new Runnable() {
#Override
public void run() {
imgView.setImageResource(resuorceId);
}
});
sleep(500);
}
} catch (InterruptedException e) {
}finally {
Intent intent = new Intent(SplashScreen.this,LoginActivity.class);
startActivity(intent);
finish();
}
}
You can not access your views from Thread.
You will need to put your code imgView.setImageResource(imgID[i]); in runOnUiThread
use like:
runOnUiThread(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
imgView.setImageResource(imgID[i]);
}
});
Thanks
You can not change something in UI from non-UI thread so replace this you code:
imgView.setImageResource(imgID[i]);
to:
runOnUiThread(new Runnable() {
#Override
public void run() {
imgView.setImageResource(imgID[i]);
}
});
//try code this way...
public class SplashScreen extends Activity {
private Intent launchIntent;
private Thread splashThread; //used for perform splash screen operation
private int splashTime = 10000, sleepTime = 50; //used for threading operation
private boolean active = true; //used for touch event
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.splashscreen); //Set splashscreen.xml here
try {
splashThread = new Thread() { // Creating Thread for splash the screen
#Override
public void run() { // run method implemented to perform threading operation
try {
int waitTime = 0; //counter for threading
do {
sleep(sleepTime); //delay for specific time
if (active)
waitTime += 100;
//write your image code here that display your no. of images
} while (active && (waitTime < splashTime)); //Check touch condition and counter
} catch (Exception e) {
// to handle runtime error of run method
Validation.displayToastMessage(SplashScreen.this, e.toString()); //Call static method of class ToastMessage
}
finish(); //finish current activity
startJustCoupleActivityScreen(); //Call below defined function
}
};
splashThread.start(); //start thread here
} catch (Exception e) {
message("SplashScreen : "+ e.toString()); //Call static method of class ToastMessage
}
}
public void startJustCoupleActivityScreen() {
launchIntent=new Intent(SplashScreen.this,JustCoupleActivity.class); //call Next Screen
startActivity(launchIntent); //start new activity
}
#Override
public boolean onTouchEvent(MotionEvent event) { //onTouch Event
//on touch it immediate skip splash screen
if(event.getAction()==MotionEvent.ACTION_DOWN) active=false; //Check Touch happened or not
return true;
}
public void message(String msg)
{
Validation.displayToastMessage(SplashScreen.this, msg); //display Error Message
}
}
Ok this is a very weird problem I am having, and I'm pretty sure that I am messing up somewhere, but I can't quite figure out where.
What I am trying is -
Schedule a Timer to execute a TimerTask every five seconds
The TimerTask in turn executes an AsyncTask (which in this case simple sleeps for a second before returning the static count of the number of AsyncTasks).
Finally, the aforementioned count is updated in the UI.
And of course, the appropriate Handlers and Runnables have been used to post asynchronous messages from other threads to the UI.
This code executes only once. I expect it to fire every 5 seconds. Here's the code.
Note: I had no idea what to do with the Looper. I put it there after trial and error!
public class TimerAsyncMixActivity extends Activity {
public static final String TAG = "TimerAsyncMix";
static int executionCount = 0;
Handler mHandler = new Handler();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new Timer().schedule(new MyTimerTask(this), 0, 5000);
}
class MyAsyncTask extends AsyncTask<String, Void, Integer>{
#Override
protected Integer doInBackground(String... params) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return ++executionCount;
}
#Override
protected void onPostExecute(Integer result) {
mHandler.post(new UpdateUiThread(TimerAsyncMixActivity.this, result));
super.onPostExecute(result);
}
}
}
class MyTimerTask extends TimerTask{
private TimerAsyncMixActivity tma;
public MyTimerTask(TimerAsyncMixActivity tma) {
this.tma = tma;
}
#Override
public void run() {
Looper.prepare();
Log.d(TimerAsyncMixActivity.TAG, "Timer task fired");
tma.new MyAsyncTask().execute();
Looper.loop();
Looper.myLooper().quit();
}
}
class UpdateUiThread implements Runnable{
int displayCount;
TimerAsyncMixActivity tma;
public UpdateUiThread(TimerAsyncMixActivity tma, int i) {
this.displayCount = i;
this.tma = tma;
}
#Override
public void run() {
TextView tv = (TextView) tma.findViewById(R.id.tvDisplay);
tv.setText("Execution count is : "+displayCount);
}
Can anyone point me to what I'm doing wrong?
techie, this is how I implemented similar things. I'm won't claim that this is the best way, but it has worked for me and doesn't look too bad.
I have the following code in my activity. I create an async task when the activity starts and I stop it onPause. The AsyncTask does whatever it needs to do, and updates the UI on onProgressUpdate() (which is run on the UI thread, so there's no need to use a Handler).
private Task task;
#Override
protected void onPause() {
task.stop();
task = null;
}
#Override
protected void onResume() {
task = new Task();
task.execute();
}
private class Task extends AsyncTask<Void, String, Void> {
private boolean running = true;
#Override
protected Void doInBackground(Void... params) {
while( running ) {
//fetch data from server;
this.publishProgress("updated json");
Thread.sleep(5000); // removed try/catch for readability
}
return null;
}
#Override
protected void onProgressUpdate(String... values) {
if( ! running ) {
return;
}
String json = values[0];
//update views directly, as this is run on the UI thread.
//textView.setText(json);
}
public void stop() {
running = false;
}
}
Do not use a timer. If your phone goes to sleep, the timer is suspended too. Use AlarmManager.