We're working on a new WPF app, using MVVM Light. We've got a customized ObservableCollection which starts as being bound to a datagrid. According to the project's specification we have to start on a form showing the datagrid and then when a user selects a row we show the user a detail view in another form. At this point we're getting the selected row and assigning that to an object which we assign to a MVVM Light message so that the detail view will be able to display the record's details.
Now that we're getting into this we've encountered a complication. The specs require that the detail view be able to navigate through the collection, even though at this point it doesn't have the collection. We had through we could accomplish this through an interface we defined that we called IRecordService, implementing it for each type of record we work with. However the problem is that the record has no idea if its the first record in the collection, the last one, etc. And that's necessary because of buttons on the detail form where people can navigate through the collection. We've been trying to do this with, for example CustomerRecordService, but so far that hasn't worked out. Perhaps it will if we keep at it.
But I've been wondering, what if instead of creating an object that has the selected record in it which gets passed into a message, we instead pass the whole collection and the key to the selected record into the message which then is caught by the detail viewmodel? My co-workers primary concern is how is the ObservableCollection passed, under these circumstances? Is a copy of the ObservableCollection passed or a reference to theObservableCollection that's in the listing viewmodel? I would think its a reference, but wanted to ask to make sure I'm right, or not.
It has to be just a reference. Otherwise messenger would have to know how to clone every single object. But you can easilly check it. After you get an object in your details viewmodel, change it. Add something, remove something and change some parameter of some objects in the collection. Then check if it has been changed in the main form with the grid.