Question

I am creating a custom control and it is a button. It may has a type and a specified image according to its type. Its type may be:

public enum ButtonType
{
    PAUSE,
    PLAY
}

Now I can change its appearance and Image with a method:

public ButtonType buttonType;
public void ChangeButtonType(ButtonType type)
{
    // change button image
    if (type == ButtonType.PAUSE)
        button1.Image = CustomButtonLibrary.Properties.Resources.PauseButton;
    else if (type == ButtonType.PLAY)
        button1.Image = CustomButtonLibrary.Properties.Resources.PlayButton;

    buttonType = type;
}

OK, this method doesn’t seems so good, for example maybe later I wish to have another type STOP for example for this button, I want just add its image to resources and add it to ButtonType enum, without changing this method.

How can I implement this method to be compatible with future changes?

Answer 1

One thing you can do is turn ButtonType into a base class (or an interface, if you prefer):

public abstract class ButtonType
{
    public abstract Image GetImage();
}

Then each of your types becomes a subclass:

public class PauseButtonType : ButtonType
{
    public Image GetImage()
    {
        return CustomButtonLibrary.Properties.Resources.PauseButton;
    }
}

public class PlayButtonType : ButtonType
{
    public Image GetImage()
    {
        return CustomButtonLibrary.Properties.Resources.PlayButton;
    }
}

Your image changing method then becomes:

private ButtonType buttonType; // public variables usually aren't a good idea
public void ChangeButtonType(ButtonType type)
{
    button1.Image = type.GetImage();
    buttonType = type;
}

This way when you want to add another type, you add another ButtonType subclass and pass it to your ChangeButtonType method.

---

Since this method is on your custom button class, I would probably take this a bit further and encapsulate style/appearance in a class:

public class ButtonStyle
{
    // might have other, non-abstract properties like standard width, height, color
    public abstract Image GetImage();
}

// similar subclasses to above

And then on the button itself:

public void SetStyle(ButtonStyle style)
{
    this.Image = style.GetImage();
    // other properties, if needed
}

You could set up button behaviours (i.e. actions they perform when they’re clicked) in a similar way with a ButtonAction base class and assigning specific actions like Stop and Play when you want to change the button’s purpose and style.