WPF MVVM update collections so that UI updates -

i want update ui. should use backgroundworker? put backgroundworker in mainwindowviewmodel , instantiate repositories again, or put in ordersqueueviewmodel , properties?

the ui displays contents of lists created linq. lists observablecollection , properties of ordersqueueviewmodel. have viewmodel mainwindowviewmodel creates collection viewmodels, can bind collection mainwindow.xaml (view).

mainwindowviewmodel.cs:

public mainwindowviewmodel() {     _printqueuerepos = new ordersprintqueuerepository();     _holdqueuerepos = new ordersholdqueuerepository();                 _linestopickrepos = new linestopickrepository();     _linesperhourrepos = new linesperhourrepository();      //create instance of viewmodel , add collection                 ordersqueueviewmodel viewmodel = new ordersqueueviewmodel(_printqueuerepos, _holdqueuerepos, _linestopickrepos, _linesperhourrepos);     this.viewmodels.add(viewmodel);               } 

mainwindow.xaml:

<window.resources>     <datatemplate datatype="{x:type vm:ordersqueueviewmodel}">         <vw:ordersqueueview></vw:ordersqueueview>     </datatemplate> </window.resources> 

example of property in orderqueueviewmodel uses repository:

public observablecollection<linestopick> linestopick {         {         return new observablecollection<linestopick>(_linestopickrepos.getlinestopick());     } } 

so havelinestopick bound in ordersqueueview, , database updates lists should change in ui. i'v spent time reading backgroundworker, i'm not quite sure update lists. i'm hoping because observablecollections can "refresh" them , use inotifypropertychanged , update ui automatically. new this, trying head around it, in advance help.

edit: using james's suggestion have ended in ordersqueueviewmodel. getting error "this type of collectionview not support changes sourcecollection thread different dispatcher thread", when code gets .clear() on 2 lists, thought dispatcher used for. suggestions?

action workaction = delegate {     _worker = new backgroundworker();     _worker.dowork += delegate     {         linesthroughput.clear();         linestopick.clear();          //refresh linestopick         foreach (var item in _linestopickrepos.getlinestopick())         {             linestopick.add(item);         }         //refresh linesthroughput        list<linesthroughput> lines = new list<linesthroughput>    (_linesperhourrepos.getlinesthroughput());         foreach (var item in getlinesthroughput(lines))        {            linesthroughput.add(item);        }    };    _worker.runworkerasync(); }; dispatcher.currentdispatcher.begininvoke(dispatcherpriority.normal, workaction); 

you can either way - in mainwindowviewmodel or 1 of child view models. choose based on way produces lower coupling , higher cohesion between components. (lower coupling - fewer dependencies. higher cohesion - things go belong logically together.)

and backgroundworker reasonable technique. remember dispatch ui thread update collection. observablecollection code... needs work. don't reinstantiate observablecollection. this:

public observablecollection<linestopick> linestopick { get; private set; }  // don't forget nstantiate in ctor  public void refresh() {     linestopick.clear();     foreach(var item in _linestopickrepos.getlinestopick())     {         linestopick.add(item);     } } 

by keeping same observablecollection databound, ui automatically pick changes collection. if replace collection, lose binding , ui won't update until notify property containing collection changed. easier keep same collection.