Question

A winclient is using GUI controls (BaseForm, BaseTextBox, BaseComboBox) from a separate GUI project which is used in other projects as well

These controls change backgroundcolor to yellow-ish when they are focused and retains their old backgroundcolor when focus leaves. (onEnter and OnLeave events)

Now, this winclient will let the users choose their own focus color. I know I can directly set the “FocusColor” property on all the controls but that’s not what i want (there’s a lot of controls)

What’s the best approach? I thought maybe I could inject some kind of “CustomColorProvider” into the controls and rewrite the GUI project to fetch the focuscolor from a “StandardColorProvider”. But I don’t exactly how these controls should get their “CustomColorProvider” injected. (I’m not so experienced with DI) The controls are added via the designer and the creation of controls is by auto-generated code “partial designer class”

Or maybe I should just write new controls in this specific winclient which inherits from the GUI project and then override the methods where the focuscolor is set?

I have access and allowed to modify both the winclient and the GUI project.

Answer 1

As you mentioned, I would use the Decorator pattern, passing a different concrete decorator depending on how you want to extend the control. You can find an example here.

EDIT:

Declare an interface IControlExtender

public interface IControlExtender
{
    Color BackColor { get; }
    Color HighlightColor { get; }
}

Create a default implementation

class DefaultExtender : IControlExtender
{
    public Color BackColor
    {
        get { return Color.Yellow; }
    }

    public Color HighlightColor
    {
        get { return Color.Red; }
    }
}

Add a property to your GUI control

IControlExtender _extender = new DefaultExtender();
public IControlExtender Extender
{
    get { return _extender; }
    set
    {
        if ((value != null) && (value != _extender))
        {
            _extender = value;
            RefreshControl();
        }
    }
}

void RefreshControl()
{
    this.BackColor = Extender.BackColor;
}

Create any new implementations, such as

class CustomExtender:IControlExtender
{
    public Color BackColor
    {
        get { return Color.Green; }
    }

    public Color HighlightColor
    {
        get { return Color.Pink; }
    }
}

And override the default as you need

public Form1()
{
    InitializeComponent();
    control1.Extender = new CustomExtender();
}