Question

I’m building a Windows Store App and I have a TextBox binded (two-way mode) to a string “title” property of my TaskItem object.

I need to do some processing after changes in the UI are made to this TextBox and propagated back to the source.

I’d like to know if there’s a way to detect when the target (TextBox’s Text property) has changed. I know I can catch this event by handling the TextBox’s LostFocus event, but this event is triggered before the source is updated.

Update:

Binding:

<ScrollViewer
            x:Name="itemDetail"
            DataContext="{Binding SelectedItem, ElementName=itemListView}">
    <TextBox x:Name="itemTitle" Text="{Binding Title, Mode=TwoWay}"/>
</ScrollViewer>

Class and property:

class TaskItem
{
    public string Title { get; set; }
}

I didn’t implement the INotifyPropertyChanged because I actually don’t need changes to be propagated from the source to the target.

I can think of two solutions:

• Is there a way to use [CallerMemberName] on a property’s setter? If there is, I may be able to determine whether the “title” was changed by my own code or because of the binding.
• Ditch the two-way binding and update the source manually during the LostFocus event.

Answer 1

class TaskItem, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    internal void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }

    private string title;
    public string Title 
    { 
       get { return title; } 
       set 
       { 
           if (title == value) return;
           title = value;
           NotifyPropertyChanged("Title");
       }
    }
    public TaskItem (string -title) 
    { title = _title; }  
    // does not fire setter title lower case 
    // but the UI will have this value as ctor fires before render 
    // so get will reference the assigned value of title 
}

Constructor Design