Question

i am working on MVVM and using commanding in silverlight(DelegateEvent and ICommand)

I want something like this ,(say) i have 2 usercontrols , parent and child .

Parent is hosting the child , both have thier own viewmodels .

On parent i have a button and it executes a simple command , on execute of that command i want to update text in the child control’s textbox . also we should be able to change something in child which can propagate to the parent .

Is events the best answer for this or i can have commands to update child/notify parent in some way.

Answer 1

There are several ways to go about this.

First, it is completely appropriate to have ViewModels that are composed of other ViewModels, as long as you are OK with them being coupled in that way. When you do that, they can just talk to each other using regular method calls.

Next, you can decouple a bit and use events. Nothing wrong with that. There is still an Observer -> Observable coupling, but they are less dependent upon each other.

Next, you can completely decouple and use something like an EventAggregator (Prism has a good one you can use). Shoot a Publish a message. The other subscribes. They don’t know about each other at all.

I have used commands for this as well… but for ViewModel to ViewModel communication, I find this to be a bit awkward.