WPF Binding - ListBox Selected Item Update is not reflected in the textblock that binds to it

Question

I have a combobox and its datacontext property is assigned to ObservableCollection.

<ComboBox 
    Name="CB" 
    ItemsSource="{Binding}" 
    DisplayMemberPath="Name" 
    IsSynchronizedWithCurrentItem="True">
</ComboBox>
<TextBlock 
    Name="TB" 
    Text="{Binding ElementName=CB,Path=SelectedItem.Name,UpdateSourceTrigger=PropertyChanged}"
    ></TextBlock>

C#

class Person
{
    public string Name { get; set; }
}

ObservableCollection<Person> people = new ObservableCollection<Person>( new List<Person>()
{
    new Person(){Name="A"},
    new Person(){Name="B"},
    new Person(){Name="C"},
    new Person(){Name="D"},
});

people[0].Name = "Z"; // When button clicked, i execute this

I also have a button when clicked updates the first employee's Name to something else.

When the first employee is the selected one, and I clicked the button even though underlying name changes, it's not reflected in the UI until I change the selected item and re-select the first one.

What should I do to achieve what I want? I thought when ObservableCollection that combobox is bound to changes, it would have been reflected in the ui.

ObservableCollection obviously doesn't have any magic ability to monitor property changes in the items it contains. The items need to implement `INotifyPropertyChanged` and raise the `PropertyChanged` event when their own properties change. — 15ee8f99-57ff-4f92-890c-b56153, Apr 24 '18 at 15:33
I'm referring to the class contained in the ObservableCollection. The items in the ObservableCollection are instances of some class. That class needs to implement INotifyPropertyChanged. — 15ee8f99-57ff-4f92-890c-b56153, Apr 24 '18 at 15:35
How to implement INotifyPropertyChanged: https://stackoverflow.com/questions/1315621/implementing-inotifypropertychanged-does-a-better-way-exist — AidanH, Apr 24 '18 at 15:37
@EdPlunkett So PropertyChanged will indicate to ObservableCollection somethingchanged and in return would trigger CollectionChanged so that combobox would know there is an update, right? — neo, Apr 24 '18 at 15:39
@neo Not even close. What about objects that aren't contained in an ObservableCollection? Are you suggesting that they can't notify the UI of changes? — 15ee8f99-57ff-4f92-890c-b56153, Apr 24 '18 at 15:40
`PropertyChanged` is handled by the `Binding` that binds the viewmodel property to a property of a control in the UI. `CollectionChanged` is unrelated. It's a notification a collection raises when the collection has changed: Add/remove/swap. This is all documented. — 15ee8f99-57ff-4f92-890c-b56153, Apr 24 '18 at 15:42

score 0 · Answer 1 · answered Apr 24 '18 at 19:45

The underlying object (i.e. Person) of the ObservableCollection needs to implement INotifyPropertyChanged interface.

    class Person : INotifyPropertyChanged
    {
        private string name;
        public string Name 
        { 
          get
          {
             return name;
          } 
          set
          {
              if(value != name)
              {
                  name = value;
                  RaisePropertyChange("Name");
              }
          }
        }

          public event PropertyChangedEventHandler PropertyChanged;

          public void RaisePropertyChange(string propertyname) 
          {  
             if (PropertyChanged != null) 
             {  
                PropertyChanged(this, new PropertyChangedEventArgs(propertyname));  
             }  
          }
    }

You can modify the generated code, I guess. If not, then you can create a wrapper class around the model class created by EF. — tushardevsharma, Apr 25 '18 at 09:38

WPF Binding - ListBox Selected Item Update is not reflected in the textblock that binds to it

1 Answers1