Question

I’ve recently taken over a MVVM project started by someone who’s now left the company; It’s my first time using WPF, but by the looks of it, it was his first time using both WPF and OOP…

Anyway, I’ve got a ListView in the XAML, and I’ve got a collection class which doesn’t currently contain a “SelectedItem” property.

Can someone tell me what code I need to put in to link the SelectedItem of the ListView to the as-yet-unwritten SelectedItem property of my collection, and then what code I need to put in so that the SelectedItem of the collection links back to the ListView?

Apologies for the homework-level question, but the code I’m working with is such a nightmare that I can’t yet wrap my head around “how to write WPF?” at the same time as “how do I rewrite this coding horror as OOP?” so if someone can supply me with some example code, I can work on inserting it into the nightmare…

Answer 1

You could use WPF binding to perform your task. Excuse me the code will be in C#, but it shouldn’t be hard to understand and to adapt in VB.NET 😉 :

In Xaml, Your binding must use the TwoWay Mode because you want that any UI update is reflected on the viewmodel.

<ListView SelectedItem="{Binding SelectedItem, Mode=TwoWay}" ItemsSource="{Binding MyObjects}"/>

Your ViewModel need to implement INotifyPropertyChanged in order for the WPF Binding system to be notified of property changes on the ViewModel.

public class MyViewModel: INotifyPropertyChanged
{
  private MyObj selectedItem;
  public MyObj SelectedItem
  {
    get{return this.selectedItem;}
    set
    {
      if(value!=selectedItem)
      {
        selectedItem = value;
        RaisePropertyChanged("SelectedItem");
      }

    [... your collection....]
    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged(string propertyName)
    {
      var propertyChanged = this.PropertyChanged;
      if(propertyChanged!=null) 
        propertyChanged(new PropertyChangedEventArgs(propertyName));
    }