C# properties issue

The other day I bumped into a little problem regarding C#'s properties.

Let's say I have this setup:

public class Point
{
 public float X;
 public float Y;
}

public class Control
{
 protected Point m_Position = new Point();

 public Point Position
 {
  get { return m_Position; }
  set 
  { 
    m_Position = value; }
    // reorganize internal structure..
    reorganize();
  }

  protected reorganize()
  {
   // do some stuff
  }
}

This is all fine, but when it comes to usage, I coul开发者_StackOverflow中文版d write something like:

Control myControl = new Control();
myControl.Position.X = 1.0f;

The thing is, my Control class won't recognize that the Position has been changed because set() hasn't been called.

Is there a way to make Control aware of any Position changes?

There are a number of options in this case:

1. Make the X and Y properties of your Point class immutable. That is, require the user to create a new Point whenever X or Y changes.
2. Setup an event on the Point class and subscribe to it on the Position class. Whenever the Point's X or Y changes, fire the event. The Position class can handle side-effects in the event handler.

In this case, I would suggest option #1

The statement myControl.Position.X = 1.0f; actually calls the getter and not the setter of your Position property. A way to do what you want to do could be by exposing the X and Y values directly on your class, like so:

public class Control  
{  
 protected Point m_Position = new Point();  

 public float PositionX
 {  
  get { return m_Position.X; }  
  set   
  {   
    m_Position.X = value; }  
    // reorganize internal structure..  
    reorganize();  
  }  

  ... Same thing for PositionY

  protected reorganize()  
  {  
   // do some stuff  
  }  
}

Another way would be to implement some event on the Position class that is raised every time X or Y change. This would entail making X and Y into properties on the Point object, and raising an event each time they are changed. Your control would then have to subscribe to that event.

1) Make Point.X and Point.Y private. 2) Add properties for X and Y to Point. 3) Add an event to Point that is raised when either X or Y are modified. 4) Register Control as a listener for the events that are raised by Point.

You could make public class Point a public struct Point. This way, the compiler will force you to write

myControl.Position = new Point() { X = 1.0f, Y = myControl.Position.Y; }

and the property setter is called.

This should fix it! I have added a line into your getter that tests to see if the point is null and if it is instantiate it before returning.

public class Point
{
 public float X;
 public float Y;
}

public class Control
{
 protected Point m_Position = new Point();

 public Point Position
 {
  get 
  { 
      if (m_Position == null) m_Position = new Point();
      return m_Position; 
  }
  set 
  { 
    m_Position = value; 
    // reorganize internal structure..
    reorganize();
  }

  }

  protected reorganize()
  {
   // do some stuff
  }
}

HTH