c# - DispatcherTimer and Show Modal Window -

let's see if can explain me behaviour , maybe how can solve this. have wpf app, , in viewmodel have dispatchertimer. in viewmodel have command show modal window, this:

private void showwindowcommandexecuted() {      wnnewwindow window = new wnnewwindow();      window.showdialog(); } 

when call command button, new window shown , dispatchertimer keeps running in background. far good. problem when try show window dispatchertimer this:

dispatchertimer timerinstrucciones; timerinstrucciones = new dispatchertimer(); timerinstrucciones.interval = timespan.frommilliseconds(1000); timerinstrucciones.tick += (s, e) => {      wnnewwindow window = new wnnewwindow();      window.showdialog();      }; timerinstrucciones.start(); 

in case, new window shown, long visible, dispatchertimer stops "ticking". understand dispatchertimer runs in ui thread, why behaves in different way in case?

generally, showdialog modal dialog block calling thread, , show dialog. block interaction parent/owning window too.

as long close modal dialog, ui-thread blocked. because dispatchertimer, belongs window's dispatcher , runs in same thread. if thread blocked, dispatchertimer stops running.

update based on comments:

i haven't went through documentation on this, basic difference dispatchertimer run synchronously , not in asynchronous way.

won't block dispatcher:

 timerinstrucciones.tick += (s, e) =>         {             this.dispatcher.begininvoke(new action(() =>            {                wnnewwindow mn = new wnnewwindow();                mn.showdialog();            }));         }; 

will block dispatcher:

timerinstrucciones.tick += (s, e) =>         {             this.dispatcher.invoke(new action(() =>            {                wnnewwindow mn = new wnnewwindow();                mn.showdialog();            }));         }; 

since, dispatcher invoke event on every n seconds, event cannot called anymore, if thread got blocked operation inside calling event .