C＃数据绑定标签不会刷新

Question

I am databinding an object value to a label and it wont refresh.

lblTime.DataBindings.Add(new Binding("Text", AppSettings.Instance.SelectedAuction, "EndDate", false, DataSourceUpdateMode.OnPropertyChanged));

The bind works and using a messagebox, I know the value is changing. I am correctly using the INotifyChanged but it wont work. Changing individual values works, say:

AppSettings.Instance.SelectedAuction.EndDate = ((Auction)lbAuctions.SelectedItem).EndDate;

But I want to replace the whole object, and it wont update:

AppSettings.Instance.SelectedAuction = (Auction)lbAuctions.SelectedItem;

Why is this? I can make individual values refresh but not the object itself...

public Auction SelectedAuction
    {
        get { return this.selectedAuction; }
        set
        {
            this.CheckPropertyChanged<Auction>
            ("SelectedAuction", ref this.selectedAuction, ref value);
        }
    }

Is it that there is another method to use when replacing the object itself or something additional i need to ref?

Answer 1

The data binding that is setup on lblTime is set on the object reference by AppSettings.Instance.SelectedAuction at the time of the call to AddBinding . The databinding subscribes to the PropertyChanged event on that object. Changing the SelectedAuction on your Instance doesn't change that. The data binding is still subscribed on the original object. (This also means you have a memory lead, since the data binding references the original CurrentAuction , that instance will not be garbage collected)

You need to instead setup the data binding so that it can listed for events on the Instance object. You would have to set the binding to "CurrentAuction.EndDate" . This will not work directly (* see note below), but there is a helper object, BindingSource , that can be put in the middle that will support that binding. Below is an example:

BindingSource bs = new BindingSource();
bs.DataSource = AppSettings.Instance;
lblTime.DataBindings.Add("Text", bs, "CurrentAuction.EndDate", false, 
      DataSourceUpdateMode.OnPropertyChanged);

Note: It will work without a BindingSource in 3.5, but not in 4.0, see Does data binding support nested properties in Windows Forms?