Question

I am new to MVVM, and I am trying to implement a simple application, following the pattern.

For simplicity, I am breaking the problem down to it’s simplest form. If I manage to get this to work, I will have little trouble getting the application made.

The simple application consists of a tabcontrol. It is important that both tabs have their own ViewModel. However, they will get most of their data from the same source. The main issue is to get the second tab to know that the first have initiated a change on the datasource.

So, for simplicity, let’s just say that the model is holding a single integer. This integer needs initially to be set to 1.

The first tab is holding a textblock and a button. The text of the textblock is bound to the integer in the datamodel. Upon pressing the button, the integer in the moddel should be incremented with 1.

The second tab holds only a textblock, also bound to the integer in the datamodel. The challenge is to get this textblock to update along with the first textblock, but still being it’s own viewmodel.

I need somewhere central to store the values of the model, and in some way, let the viewmodels know that they have been updated, so their properties can be updated, and the Views therefore get’s updated accordingly.

Can someone explain in as much detail as possible how this is done? I have tried a billion different ways, but I am not getting it to work.

Answer 1

Let me see if I have your question down right:

• You have a data source (your model).
• You have 2 view models.
• View model 1 changes data in the model.
• View model 2 needs to update with changes in the model.

If that all sounds right, here’s one solution:

Have your model implement INotifyPropertyChanged. When the integer changes, raise the PropertyChanged event. In view model 2, listen for the model’s PropertyChanged event. When it occurs, raise view model 2’s property changed event, and its UI will get updated automatically.