How to stop timer when Activity is closed?

Question

Java

In onCreate , a timer is created that starts an AsyncTask thread every 15 seconds, after the activity or the entire application closes, the timer still continues to start this thread. If the timer.cancel(); command is executed in onDestroy or on a button click, the activity throws an error.
here is the timer code
in onCreate

Timer timer = new Timer();
          MyTimerTask task = new MyTimerTask();
          
          timer.schedule(task,0, 15 * 1000);
          }

TimerTask

class MyTimerTask extends TimerTask {
    	
        public void run() {
        	
        	 String streamUrl = "ссылка";
        	metadataTask =new MetadataTask();
          try {
              metadataTask.execute(new URL(streamUrl));
          } catch (MalformedURLException e) {
              e.printStackTrace();
          }
                           	
             String title_artist;
      try {
        streamMeta.refreshMeta();
        title_artist = streamMeta.getStreamTitle();
        Log.i("ARTIST TITLE", title_artist);
      } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }
        
                       
        }
    }

in onDestroy I do timer.cancel();
and at closing

12-31 19:09:04.220: E/AndroidRuntime(1816): FATAL EXCEPTION: main
12-31 19:09:04.220: E/AndroidRuntime(1816): java.lang.RuntimeException: Unable to destroy activity {com.example .kgw/com.example.kgw.TimerActivity}: java.lang.NullPointerException
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3499)
12- 31 19:09:04.220: E/AndroidRuntime(1816): at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3517)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.app. ActivityThread.access$1200(ActivityThread.java:141)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1309)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.os.Handler.dispatchMessage(Handler.java:99)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android. os.Looper.loop(Looper.java:137)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.app.ActivityThread.main(ActivityThread.java:5103)
12-31 19:09: 04.220: E/AndroidRuntime(1816): at java.lang.reflect.Method.invokeNative(Native Method)
12-31 19:09:04.220: E/AndroidRuntime(1816): at java.lang.reflect.Method.invoke( Method.java:525)
12-31 19:09:04.220: E/AndroidRuntime(1816): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
12-31 19:09: 04.220: E/AndroidRuntime(1816): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-31 19:09:04.220: E/AndroidRuntime(1816): at dalvik.system.NativeStart.main(Native Method)
12-31 19:09:04.220: E/AndroidRuntime(1816): Caused by: java.lang .NullPointerException
12-31 19:09:04.220: E/AndroidRuntime(1816): at com.example.kgw.TimerActivity.onDestroy(TimerActivity.java:313)
12-31 19:09:04.220: E/AndroidRuntime(1816) : at android.app.Activity.performDestroy(Activity.java:5302)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1117)
12-31 19:09:04.220: E/AndroidRuntime(1816): at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3486)
12-31 19:09:04.220: E/AndroidRuntime(1816): ... 11 more

Answer 1

You most likely have the variable timer == null at the time of window destruction. Are you sure you set it globally? Because here in onCreate you seem to have a local variable.

Answer 2

look here