添加到视图模型的属性不会在组合框中生成项目

Question

My view model class is very simple.

class Presenter
{
  public IEnumerable<String> JustFake => new List<String> { "aaa", "bbb" };

  public Presenter() { }
}

IN XAML I've added a combo box bound to the property as follows.

<Window.DataContext>
  <local:Presenter/>
</Window.DataContext>
...
<ComboBox x:Name="comboBox"
          ItemsSource="{Binding JustFake}"/>

However, although intellisense found JustFake , the values don't appear in the combo box. It's empty. I've tried implementing INotify... etc. but nothing gave me any difference. I can't really tell what I can be missing. Should I inherit something else (I saw a blog where they mentioned BindableBase , whatever that class might be)? Should I introduce the Presenter in another way?

Answer 1

public IEnumerable<String> JustFake = new List<String> { "aaa", "bbb" };

Declares a public field , which cannot be bound against. You need a property :

public IEnumerable<String> JustFake { get; set;}

public Presenter()
{
    JustFake = new List<String> { "aaa", "bbb" };
}

If you want to set the property after the constructor, you would need to utilize INotifyPropertyChanged , and if you want to modify the collection, make sure to use an ObservableCollection instead of List , as it implements INotifyCollectionChanged .

Update : You were apparently using a C# 6 expression member, so you may be OK on that front.

Update 2 : From the exception you reported, it appears that your DataContext is either not set, or being set later to this . Check and make sure nothing is overriding it.

Answer 2

Binding to ItemSource on an ItemsControl , such as a ListBox , or a DataGrid requires a public property:

class Presenter
{
  public List<string> JustFake { get; set; }

  public Presenter() 
  {
     JustFake = new List<string> { "aaa", "bbb" };
  }
}

To support notifications back to the UI, the collection requires an INotifyPropertyChanged implementation, it is often easier to use or derive from a collection class that already implements it. The ObservableCollection<T> :

class Presenter
{
  public ObservableCollection<string> JustFake { get; set; }

  public Presenter() 
  {
     JustFake = new ObservableCollection<string> { "aaa", "bbb" };
  }
}