multithreading - How do I correctly pass information from a long-running thread to the UI thread in Android? -

my app has chat feature. when app first starts up, spawn listener thread listen incoming data:

public class mainactivity extends appcompatactivity {     public static linkedlist<message> chatlist;      protected void oncreate(bundle savedinstancestate){         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          chatlist = new linkedlist<message>();          handler listenerthreadhandler = new handler();          mylistener mylistener = new mylistener(listenerthreadhandler, mainactivity.this);         thread listenerthread = new thread(mylistener);         listenerthread.start();     } } 

my chat feature fragment/tab within main activity. has standard window viewing chat, plus edittext , button sending chats:

<linearlayout android:id="@+id/chat_window" android:orientation="vertical">     <listview         android:id="@+id/received_chats"         android:stackfrombottom="true"         android:transcriptmode="alwaysscroll">     </listview>     <linearlayout android:id="@+id/control_window" android orientation="horizontal">         <edittext android:id="@+id/chat_entry_window" />         <button android:id="@+id/send_chat_button" android:text="send" />     </linearlayout> </linearlayout> 

when send text, add main linkedlist.

    public class chat extends fragment {      private view rootview;      @override     public view oncreateview(layoutinflater inflater, viewgroup container, bundle savedinstancestate){         rootview = inflater.inflate(r.layout.chat, container, false);         return rootview;     }      @override     public void onviewcreated(view rootview, bundle, savedinstancestate){         super.onviewcreated(rootview, savedinstancestate);         displaychats();     }      @override     public void onresume(){         super.onresume();         displaychats();     }      @override     public view getview(){         button sendchatbutton = (button) rootview.findviewbyid(r.id.send_chat_button);         sendchatbutton.setonclicklistener(new view.onclicklistener(){             @override             public void onclick(view v){                 edittext chatentrywindow = (edittext) rootview.findviewbyid(r.id.chat_text_entry);                 // add chat linkedlist                 mainactivity.chatlist.add(chatentrywindow.gettext().tostring());             }         });     }      public void dispalychats(){         final arrayadapter adapter = new customarrayadapter(getactivity, r.layout.line_of_chat_text, mainactivity.chatlist);         final listview list = (listview) rootview.findviewbyid(r.id.received_chats);         list.smoothscrolltoposition(list.getcount() - 1);     } } 

i add incoming chats app in listener

public class mylistener implements runnable {     handler myhandler;     context mycontext;     public mylistener(handler myhandler, context mycontext){         this.myhandler = myhandler;         this.mycontext = mycontext;     }      @override     public void run(){         listenforchats();     }      public listenforchats(){         // here want add chats main list.         mainactivity.chatlist.add(received_chat);     } } 

what want able pass text received listenerthread ui thread inserted linkedlist. know need because error every in app:

java.lang.illegalstateexception

the content of adapter has changed listview did not receive notification.

make sure content of adapter not modified background thread, ui thread.

i have used handler before, don't know if using correctly here. in past, have passed in layout element (e.g., textview, imageview, etc.) , have updated handler.

in listener thread, changed

mainactivity.chatlist.add(received_chat); 

to

myhandler.post(new runnable(){     @override     public void run(){         mainactivity.chatlist.add(received_chat);     } }); 

my chats still getting added main linkedlist, don't know if different way did or not. how know if have passed data ui thread?

so, how correctly pass data listener thread ui thread adding linkedlist?