Updating ViewModel content in MVVM

Question

I have a list on my XAML page bind to my ViewModel. The list Show only the entries - there is no Feature to edit or update them (they are read from Server api).

In the application bar I have a button for reloading the list (sending again the request to the Server).

What must I do for this "reload Feature"?

I think about following:

• removing the existing collection of my entries
• firering the LoadData again

Are there any snippets for my question? What is about Memory issues because of my previous existing collection?

Answer 1

Something like this would work if you think your callback will be pretty light. If you think it may be heavy with a lot of items coming back then this may not be the most efficient way but would still work:

 public class YourViewModel
 {
     public ObservableCollection<YourDataType> YourCollection { get; set; } 

     public ICommand ReloadDataCommand { get; set; }

     public YourViewModel()
     {
         YourCollection = new ObservableCollection<YourDataType>();
         ReloadDataCommand = new DelegateCommand(ReloadData);
     }

     private void ReloadData()
     {
         //Get your new data;
         YourCollection = new ObservableCollection(someService.GetData());
         RaisePropertyChange("YourCollection");
         //Depending on how many items your bringing in will depend on whether its a good idea to recreate the whole collection like this. If its too big then you may be better off removing/adding these items as needed.
     }
 }

In XAML:

     <Button Content="Reload" Command="{Binding ReloadDataCommand}" />
     <List ItemsSource="{Binding YourCollection}">
       <!-- All your other list stuff -->
     </List>

Hope this helps