WPF OpenFileDialog with the MVVM pattern? -

i started learning mvvm pattern wpf. hit wall: what do when need show openfiledialog?

here's example ui i'm trying use on:

when browse button clicked, openfiledialog should shown. when user selects file openfiledialog, file path should displayed in textbox.

how can mvvm?

update: how can mvvm , make unit test-able? solution below doesn't work unit testing.

what create interface application service performs function. in examples i'll assume using mvvm toolkit or similar thing (so can base viewmodel , relaycommand).

here's example of extremely simple interface doing basic io operations openfiledialog , openfile. i'm showing them both here don't think i'm suggesting create 1 interface 1 method around problem.

public interface ioservice {      string openfiledialog(string defaultpath);       //other similar untestable io operations      stream openfile(string path); } 

in application, provide default implementation of service. here how consume it.

public myviewmodel : viewmodel {      private string _selectedpath;      public string selectedpath      {           { return _selectedpath; }           set { _selectedpath = value; onpropertychanged("selectedpath"); }      }       private relaycommand _opencommand;      public relaycommand opencommand      {           //you know drill.           ...      }       private ioservice _ioservice;      public myviewmodel(ioservice ioservice)      {           _ioservice = ioservice;           opencommand = new relaycommand(openfile);      }       private void openfile()      {           selectedpath = _ioservice.openfiledialog(@"c:\where\my\file\usually\is.txt");           if(selectedpath == null)           {                selectedpath = string.empty;           }      } } 

so that's pretty simple. last part: testability. 1 should obvious, i'll show how make simple test this. use moq stubbing, can use whatever you'd of course.

[test] public void openfilecommand_userselectsinvalidpath_selectedpathsettoempty() {      mock<ioservice> ioservicestub = new mock<ioservice>();       //we use null indicate invalid path in our implementation      ioservicestub.setup(ioserv => ioserv.openfiledialog(it.isany<string>()))                   .returns(null);       //setup target , test      myviewmodel target = new myviewmodel(ioservicestub.object);      target.opencommand.execute();       assert.isequal(string.empty, target.selectedpath); } 

this work you.

there library out on codeplex called "systemwrapper" (http://systemwrapper.codeplex.com) might save having lot of kind of thing. looks filedialog not supported yet, you'll have write interface one.

hope helps.

edit:

i seem remember favoring typemock isolator faking framework. here's same test using isolator:

[test] [isolated] public void openfilecommand_userselectsinvalidpath_selectedpathsettoempty() {     ioservice ioservicestub = isolate.fake.instance<ioservice>();      //setup stub arrangements     isolate.whencalled(() => ioservicestub.openfiledialog("blah"))            .wascalledwithanyarguments()            .willreturn(null);       //setup target , test      myviewmodel target = new myviewmodel(ioservicestub);      target.opencommand.execute();       assert.isequal(string.empty, target.selectedpath); } 

hope helpful well.