Executing relaycommand in a viewmodel from a service class

Question

I build up a custom TreeView class, with settings for each node such as "name/background" etc. I also have a ICommand property that can be set so that each node can have a custom method executed if necessary.

I build all of this in a "treeview service class", which then sends the menu to the usercontrol via MVVMLight Messenger. This all works just fine, but my problem is that if i dont specify a custom command for the node, i want it to execute a "default action", which should be located in the viewmodel that recieves the message from the Messenger service.

Basically my question is: How do i expose a RelayCommand in the MainViewModel , so that i can reference it from another viewmodel (or my service class), when building my tree.

score 0 · Answer 1 · answered Mar 20 '13 at 19:29

0

I believe RelayCommand is an ICommand. You can just expose it as a property on the viewmodel:

public ICommand MyCommand { get; set;}

answered Mar 20 '13 at 19:29

Jras

518
3
12

Yes im with you on that, but how do i access it, if it´s not static. Im guessing i need to use the ViewModelLocator that MVVMLight offers, but im not sure on how to go about doing that. Basically my command looks like this in ViewModel B, i need to reference a RelayCommand in ViewModel A: var node = new TreeViewMenuNode() { Name = treeViewMenuNode.Name ?? "default nodename", Command = treeViewMenuNode.Command ?? new RelayCommand(() => **MainViewModel.MyPublicRelayCommand** ,() => true) }; – Swift Mar 20 '13 at 19:52

score 0 · Accepted Answer · answered Mar 20 '13 at 22:45

To reference ViewModel A in ViewModel B you can use MVVMLight´s ViewModelLocator like in the Template samples:

Your ViewModelLocator class:

 public class ViewModelLocator
 {
    static ViewModelLocator()
    {
        ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);
        // Register your services
        //...
        // Register your ViewModels
        SimpleIoc.Default.Register<MainViewModel>();
    }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance",
        "CA1822:MarkMembersAsStatic",
        Justification = "This non-static member is needed for data binding purposes.")]
    public MainViewModel Main
    {
        get
        {
            return ServiceLocator.Current.GetInstance<MainViewModel>();
        }
    }
}

and in your NodeViewModel you could access your default command for example like this:

  public class NodeViewModel : ViewModelBase
  {
    private ViewModelLocator locator = new ViewModelLocator();

    public RelayCommand NodeCommand
    {
        get
        {
            return locator.Main.DefaultCommand;
        }
    }
}

You can find a full small sample when you create a MVVM Light project by using the MVVM Light visual studio templates.

hope this helps!

Many thanks, exactly what i was looking for. Was at it for too long doing all kinds of crazy stuff, was under the impression that i was shouldnt init the locator like that, but you set me on the correct path! Thanks again! — Swift, Mar 20 '13 at 23:28

Executing relaycommand in a viewmodel from a service class

2 Answers2