How to remove all callbacks from a Handler

Question

I have a Handler from my sub-Activity that was called by the main Activity  This Handler is used by sub-classes to postDelay some Runnables  and I can t manage them  Now  in the onStop event  I need to remove them before finishing the Activity  somehow I called finish    but it still call again and again   Is there anyway to remove all callbacks from a Handler

User · Answer

If you don t have the Runnable references  on the first callback  get the obj of the message  and use removeCallbacksAndMessages   to remove all related callbacks

User · Answer

In my experience calling this worked great   handler removeCallbacksAndMessages null     In the docs for removeCallbacksAndMessages it says        Remove any pending posts of callbacks and sent messages whose obj is token  If token is null  all callbacks and messages will be removed

User · Answer

For any specific Runnable instance  call Handler removeCallbacks     Note that it uses the Runnable instance itself to determine which callbacks to unregister  so if you are creating a new instance each time a post is made  you need to make sure you have references to the exact Runnable to cancel   Example   Handler myHandler   new Handler    Runnable myRunnable   new Runnable         public void run               Some interesting task            You can call myHandler postDelayed myRunnable  x  to post another callback to the message queue at other places in your code  and remove all pending callbacks with myHandler removeCallbacks myRunnable   Unfortunately  you cannot simply  clear  the entire MessageQueue for a Handler  even if you make a request for the MessageQueue object associated with it because the methods for adding and removing items are package protected  only classes within the android os package can call them    You may have to create a thin Handler subclass to manage a list of Runnables as they are posted executed   or look at another paradigm for passing your messages between each Activity  Hope that Helps

User · Answer

As josh527 said  handler removeCallbacksAndMessages null   can work  But why  If you have a look at the source code  you can understand it more clearly  There are 3 type of method to remove callbacks messages from handler the MessageQueue     remove by callback  and token  remove by message what  and token  remove by token   Handler java  leave some overload method          Remove any pending posts of Runnable  lt var gt r lt  var gt  with Object     lt var gt token lt  var gt  that are in the message queue   If  lt var gt token lt  var gt  is null     all callbacks will be removed      public final void removeCallbacks Runnable r  Object token        mQueue removeMessages this  r  token             Remove any pending posts of messages with code  what  and whose obj is     object  that are in the message queue   If  lt var gt object lt  var gt  is null     all messages will be removed      public final void removeMessages int what  Object object        mQueue removeMessages this  what  object             Remove any pending posts of callbacks and sent messages whose     lt var gt obj lt  var gt  is  lt var gt token lt  var gt    If  lt var gt token lt  var gt  is null     all callbacks and messages will be removed      public final void removeCallbacksAndMessages Object token        mQueue removeCallbacksAndMessages this  token       MessageQueue java do the real work   void removeMessages Handler h  int what  Object object        if  h    null            return             synchronized  this            Message p   mMessages              Remove all messages at front          while  p    null  amp  amp  p target    h  amp  amp  p what    what                 amp  amp   object    null    p obj    object                 Message n   p next              mMessages   n              p recycleUnchecked                p   n                        Remove all messages after front          while  p    null                Message n   p next              if  n    null                    if  n target    h  amp  amp  n what    what                      amp  amp   object    null    n obj    object                         Message nn   n next                      n recycleUnchecked                        p next   nn                      continue                                              p   n                     void removeMessages Handler h  Runnable r  Object object        if  h    null    r    null            return             synchronized  this            Message p   mMessages              Remove all messages at front          while  p    null  amp  amp  p target    h  amp  amp  p callback    r                 amp  amp   object    null    p obj    object                 Message n   p next              mMessages   n              p recycleUnchecked                p   n                        Remove all messages after front          while  p    null                Message n   p next              if  n    null                    if  n target    h  amp  amp  n callback    r                      amp  amp   object    null    n obj    object                         Message nn   n next                      n recycleUnchecked                        p next   nn                      continue                                              p   n                     void removeCallbacksAndMessages Handler h  Object object        if  h    null            return             synchronized  this            Message p   mMessages              Remove all messages at front          while  p    null  amp  amp  p target    h                  amp  amp   object    null    p obj    object                 Message n   p next              mMessages   n              p recycleUnchecked                p   n                        Remove all messages after front          while  p    null                Message n   p next              if  n    null                    if  n target    h  amp  amp   object    null    n obj    object                         Message nn   n next                      n recycleUnchecked                        p next   nn                      continue                                              p   n

User · Answer

Please note that one should define a Handler and a Runnable in class scope  so that it is created once removeCallbacks Runnable  works correctly unless one defines them multiple times  Please look at following examples for better understanding    Incorrect way        public class FooActivity extends Activity              private void handleSomething                    Handler handler   new Handler                    Runnable runnable   new Runnable                         Override                    public void run                           doIt                                                        if shouldIDoIt                       doIt   works after 3 seconds                    handler postDelayed runnable  3000                   else                     handler removeCallbacks runnable                                           public void onClick View v                 handleSomething                         If you call onClick     method  you never stop doIt   method calling before it call  Because each time creates new Handler and new Runnable instances  In this way  you lost necessary references which belong to handler and runnable instances       Correct way     public class FooActivity extends Activity           Handler handler   new Handler            Runnable runnable   new Runnable                  Override             public void run                     doIt                                     private void handleSomething                if shouldIDoIt                     doIt   works after 3 seconds                  handler postDelayed runnable  3000                 else                   handler removeCallbacks runnable                                  public void onClick View v              handleSomething                   In this way  you don t lost actual references and removeCallbacks runnable  works successfully   Key sentence is that  define them as global in your Activity or Fragment what you use

User · Answer

Define a new handler and runnable   private Handler handler   new Handler Looper getMainLooper     private Runnable runnable   new Runnable              Override         public void run                    Do what ever you want                    Call post delayed   handler postDelayed runnable  sleep time     Remove your callback from your handler   handler removeCallbacks runnable

[java] How to remove all callbacks from a Handler?

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