Calling the set method of a property when changing elements within that property

Question

I have a class 'cropping' that contains 4 parameters:

public class Cropping
{
   public float Top { get; set; }
   public float Bottom { get; set; }
   public float Left { get; set; }
   public float Right { get; set; }
}

Within my UI class, I have an instance of the cropping class, that has a method call within the set block, to update the UI.

private Cropping croppingFactors;
/// <summary>Stores details on how to crop the image</summary>
public Cropping CroppingFactors
{
  get { return croppingFactors; }
  set 
  {
    croppingFactors = value;
    UpdateUIControls();
  }
}

The aim here is obviously to update the UI controls, everytime a change is made to one of the cropping factors, however, if I change an element within the Cropping class, ie a call to

CroppingFactors.Top = 5;

The set method of the CroppingFactors property is not being run.

How can I update the UI when I change an element within a class like this?

edit

I realise that the set property will not run because I have not set a new value to the cropping class. My question is: How do I invoke the 'UpdateUIControls()' method when I change any element within the Cropping class?

edit 2

Thanks to the answer given by Aran Mulholland - Here is my implementation for completeness:

I modified the Cropping class to implement the INotifyPropertyChanged class

public class Cropping : INotifyPropertyChanged
{
   private float top;
   public float Top
   {
     get { return top; }
     set
     {
       top = value;
       NotifyPropertyChanged();
     }
   }       

   //Same for bottom, left and right

   public event PropertyChangedEventHandler PropertyChanged;

   private void NotifyPropertyChanged()
   {
     if(PropertyChanged != null)
       PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
   }
}

And then in the UI class, I subscribed to the event:

public ImgHost()
{
  InitializeComponent();
  CroppingFactors.PropertyChanged += CroppingFactors_PropertyChanged;
}

private void CroppingFactors_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
  UpdateUIControls();
}

So that's my implementation, just for completeness. Thanks for all the answers!

Answer 1

Implement the INotifyPropertyChanged interface on the Cropping class. Subscribe to the property changed event from the UI class that is using the Cropping class as a property so that every time the property is set on any of the members of the Cropping class you can call the desired function.

Answer 2

You can always call the UpdateUIControls() whenever anything changes, but it depends what needs to trigger the change. Another alternative is add an event:

public event EventHandler PropertyUpdated;

And then whatever needs to update the control list, can call the method on the control in the event handler.