As our product has gotten bigger, I have moved it from a standard Model-View-Controller design to a more strict Cairngorm-like Model-View-Dispatcher-Command design. But one particular aspect of it has left me a bit unsure as to the best practice. I'm hoping others can share their views on this.
There are various times when a Command needs to make a "non-data-related" update to the view such as: - disabling/enabling buttons while a server operation runs - updating the focus of controls - changing component states - hiding/showing components We've had some debate about the best method to accomplish this. The easy scenario is changing states because we can simply have a model variable that the view's currentState property is data-bound to. So we can modify that model variable from within the Command which indirect updates the view. But there are other situations that are more tricky. For example, we have a login view with a username and password. We have a command that loads the stored username. If the stored username is not found, we'd like to set the focus on the username textbox, whereas if the username is found, then we want to put the focus on the password textbox. I don't believe you can set up focus using data-binding (if you can let me know). So we have postulated several different solutions to this, all of which work but we are trying to figure out which one is the most "correct" based on the design pattern. 1. Set up a ChangeWatcher to watch the a model username variable, in the handler set the focus based on whether that variable is null or not. 2. Dispatch an event from the command that the view listens to. This is used to notify the view when the username variable has been populated and thus when it can run it's focus logic. 3. Have the view object store a reference to itself in the model somewhere so that the command can update it directly. I know this seems like a very granular point but I'm just looking for the general practice in these types of situations because there are lots of them. Any thoughts? Ryan
