c# - Timer in View Model -

i have service class in external assembly, inject class in view model class mef. need call service method every 3-4 seconds view model.

i service new data dictionary. dictionary bind listbox in view. , need refresh data listbox in view.

in solution use dispatchertimer, absolute begginer in calibur.micto mvvm , wpf. don’t know suitable solution in case. if have advance gratefull.

my solution here:

[export("mainscreen", typeof(imainviewmodel))]     public class mainviewmodel : screen, imainviewmodel     {          [import]         private service _service;//import mef external assembly         [import]         private connection _conn;//import mef external assembly          //this dictionary bind listbox in view         private myobservabledictionary<string, user> _users = null;          //temp dictionry         private myobservabledictionary<string, user> _freshusers = null;          private int _selecteduserindex;          private dispatchertimer _dispatchertimer;           public account account{ get; set;}          public int selectedusersindex         {             { return _selecteduserindex; }             set             {                 _selecteduserindex = value;                 notifyofpropertychange("selectedusersindex");             }         }            public mainviewmodel()         {             _dispatchertimer = new dispatchertimer();             _dispatchertimer.tick += dispatchertimer_tick;             _dispatchertimer.interval = timespan.fromseconds(3);             _dispatchertimer.start();         }           //i every 3-4 sec server new json data , need update  data listbox in view        private void dispatchertimer_tick(object sender, eventargs eventargs)         {             //server ping, call service method             account.ping = _service.ping(account);              //refresh data in dictionary             _freshusers = _service.loadusers(account);             _users.clear();             selectedusersindex = 1;              foreach (var freshuser in _freshusers)             {                 _users.add(freshuser);             }              //check if have new messanges             if (account.ping.rp > 0)             {                 //load new messanges                 (int = 0; < account.ping.rp; i++)                 {                     #region load rp                     try                     {                         rp message = _service.loadrp(account);                          if (message != null)                         {                             //show messages                         }                     }                     catch (exception exception)                     {                         if (exception.message == "you haven&#8217;t messanged")                         {                          }                         throw exception;// how handle show exception in view?                     }                     #endregion                 }             }         }     } 

the dispatchertimer running on ui thread while running check ui freeze while dispatchertimer_tick message runs. if dispatchertimer_tick takes 2 seconds run every 3 seconds freeze ui 2 seconds. users won't that.

all service calls should done on non-ui thread don't lock ui i'd suggest using timer , doing this:

public mainviewmodel()  {     _sttimer = new system.threading.timer(timer_tick,null,3000,3000);     _dispatcher = dispatcher.currentdispatcher; }   private void timer_tick(object sender) {    account.ping = _service.ping(account);     //refresh data in dictionary     _freshusers = _service.loadusers(account);     _users.clear();     selectedusersindex = 1;      foreach (var freshuser in _freshusers)     {        _users.add(freshuser);     }      for(int i=0;i<account.ping.rp; i++)    {        //check if have new messanges         if (account.ping.rp > 0)         {             rp message = _service.loadrp(account);             _messages.add(message);        }      }      _dispatcher.begininvoke((action)(()=>{onpropertychanged("messages");})); } 

here we're using system timer check changes on different thread, ui unaffected processing. when want notify ui change has occured can use _dispatcher (the ui dispatcher create in constructor) "begininvoke" method on ui thread.

this make app appear faster. rule of thumb keep off dispatcher thread as possible; use when you're doing ui. other processing should on background thread.

hope helps