Question

I have successfully bound a control to a property on my page. The property I am binding to returns a class. The binding works but if I set the property to be a new instance of the class the UI is not updated.

Could anyone point be in the right direction to solve this issue, I have tried implementing INotifyPropertyChanged but this doesn’t work.

The Code is as follows..

XAML – Very Basic just trying to bind a label to a property at the minute.

<Grid>
        <Label Content="{Binding StudentName}"></Label>
        <Button Width="100" Height="75" Click="Button_Click" ></Button>
</Grid>

C#

this.DataContext = parentWindow.SelectedStudent;

The parent Window C# note parent window implements INotifyPropertyChanged

public event PropertyChangedEventHandler PropertyChanged;

public UCStudent SelectedStudent
{
            get
            {
                if (_selectedStudent == null)
                {
                    _selectedStudent = new UCStudent();
                }

                return _selectedStudent;
            }

            set
            {
                if (_selectedStudent != value)
                {
                    _selectedStudent = value;
                    OnPropertyChanged("SelectedStudent");
                }
            }
 }

 protected void OnPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(name));
        }
    }

The issue is when I set the SelectedStudent property to be a new selected student the binding does not update.

Answer 1

While my approach uses generics and an expression, so I can strongly type my property changes, the concept is the same. Where I use an expression, you use a string. You’ll want to return if PropertyChanged is null. Otherwise, fire the event without declaring a new event handler first.

public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged<T>(Expression<Func<T>> expression)
    {
        if (this.PropertyChanged == null) { return; }

        string propertyName = GetPropertyName(expression);

        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

This approach allows the view model to strongly type the notification.

this.NotifyPropertyChanged(() => this.SelectedApplication);