C# Getting value from delegate methods inside a class --- ref with lambda operator?

Question

I want to encapsulate delegate methods, which will be invoked later on. This delegate method, when invoked, will calculate some arguments at that instance of time and assign/return the value to a variable outside of the class.

For example, I have a class Tool

This tool should generate, let's say Point, when the delegate method is called...

public delegate void Action();

class Tool
{
public Action Select;
public Action Cancel;
public Point position;
public Tool(ref Point outPoint) //Cannot use ref with lambda...
{
Select = () => outPoint = position;
}

public void Update(Point newPosition)
{
position = newPosition
}
public void UpdateKey(Keys k, bool IsPress)
{
//Invoke Select/Cancel when press some keys
}

}

What I am trying to accomplish here is a simple function that should receive my input and fill it with correct argument after Select is invoked. If this was a single method, then it is easily done using ref. However, I have to keep track of many arguments, so I have to turn it into a class. Another thing is, this invocation happens inside the class, so I cannot return the calculated value from within the class. Even though I could change the design so that the update method is updated from outside of the class, what I desire is to have the class manages its own update routines. I know that there should be a better way, so if there is any, please tell me.

For instance: if he/she's using System.Drawing.Point, it's a struct. — Ivo
– Ivo, Commented Jun 10, 2012 at 15:40

Ivo · Accepted Answer · 2012-06-10 15:37:19Z

1

If Point is a struct, you'll need to have a class that contains OutPoint.

class OutPointContainer { //Please, think of a better name :)
    public Point OutPoint{ get; set; }
}

class Tool
{
public Action Select;
public Action Cancel;
public Point position;

public Tool(OutPointContainer outPointContainer)
{
    Select = () => outPoint.OutPoint = position;
}

public void Update(Point newPosition)
{
position = newPosition
}
public void UpdateKey(Keys k, bool IsPress)
{
//Invoke Select/Cancel when press some keys
}

}

Later, you always use the Point from OutPointContainer.OutPoint

edited Jun 10, 2012 at 15:37

answered Jun 10, 2012 at 15:11

Ivo

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Comments

Ivo · Accepted Answer · 2012-06-10 15:14:18Z

0

As Point is a class, you can always change it's values and not the complete reference:

public Tool(OutPointContainer outPointContainer)
{
    Select = () => outPoint.UpdateWith(position);
}

And the method UpdateWith will do something like this:

public void UpdateWith(Point other){
    this.X = other.X;
    this.Y = other.Y;
}

answered Jun 10, 2012 at 15:14

Ivo

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3 Comments

user385261 Over a year ago

So I have to create a container specifically for the Point that provide UpdateWith()? What if Point is a struct?

Ivo Over a year ago

No, you don't need a container, just to update the values. If it's a struct you will be passing it as a value and not reference, so you'll need to create a container class

user385261 Over a year ago

It sounds kinda like a workaround, so is there any other option?

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