vb.net - Cannot update UI from other task in win forms? -

i have 4 complex tasks running parallel, want update rich textbox log file. approximate program structure follows:

sub buttonclick ()    complextask1 'code goes here    complextask2 'code goes here    complextask3 'code goes here    complextask4 'code goes here end sub 

the above 4 tasks updates log file, have display in richtextbox control. tried infinite while loop, , updating textbox, ui getting hanged.

you must run heavy task in separate thread or background worker first read , study threading here sample coding task import these form class

imports system.threading imports system.componentmodel 

create local variable in form

private synccontext synchronizationcontext 

create method task

private sub dotask()    complextask1 'code goes here    complextask2 'code goes here    complextask3 'code goes here    complextask4 'code goes here end sub  

on button click create new thread , execute heavy task

sub buttonclick ()     synccontext = asyncoperationmanager.synchronizationcontext()     dim newthread thread     newthread = new thread(addressof dotask)     newthread.start() end sub 

to update ui status create 1 method it

private sub updatestatus(byval state object)     dim mytext string = ctype(state, string) end sub 

now call ui method use following statement in dotask method

dim newstatus string = “this new status” synccontext.post(new sendorpostcallback(addressof updatestatus), newstatus) 

complete code this

imports system.threading imports system.componentmodel public class form1     private synccontext synchronizationcontext     private sub buttonclick ()         synccontext = asyncoperationmanager.synchronizationcontext()         dim newthread thread         newthread = new thread(addressof dotask)         newthread.start()     end sub      private sub dotask()         dim newstatus string         complextask1 'code goes here         newstatus=”new task done”         synccontext.post(new sendorpostcallback(addressof updatestatus), newstatus)         complextask2 'code goes here         newstatus=”new task done”         synccontext.post(new sendorpostcallback(addressof updatestatus), newstatus)         complextask3 'code goes here         newstatus=”new task done”         synccontext.post(new sendorpostcallback(addressof updatestatus), newstatus)         complextask4 'code goes here         newstatus=”new task done”         synccontext.post(new sendorpostcallback(addressof updatestatus), newstatus)     end sub      private sub updatestatus(byval state object)         dim mytext string = ctype(state, string)     end sub end class