C# 4.0: Can I use a Color as an optional parameter with a default value?

Question

    public void log(String msg, Color c = Color.black)
    {
        loggerText.ForeColor = c;
        loggerText.AppendText("\n" + msg);

    }

This results in an error that c must be a compile-time constant. I've read up on this a little and most examples are dealing with strings and ints. I've figured out I can use the colorconverter class but I'm not sure it will be very efficient. Is there a way to just pass a basic color as an optional parameter?

    public void log(String msg, String c = "Black")
    {
        ColorConverter conv = new ColorConverter();
        Color color = (Color)conv.ConvertFromString(c);

        loggerText.ForeColor = color;
        loggerText.AppendText("\n" + msg);
    }

score 143 · Accepted Answer · edited Mar 05 '16 at 14:57

143

I've run into this as well and the only workaround I've found is to use nullables.

public void log(String msg, Color? c = null)
{
    loggerText.ForeColor = c ?? Color.Black;
    loggerText.AppendText("\n" + msg);
}

Other possible syntax is:

loggerText.ForeColor = c.GetValueOrDefault(Color.Black);

edited Mar 05 '16 at 14:57

Paul

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answered May 10 '10 at 16:29

scobi

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You can also use `default(Color)` as a default value - but sometimes this can make it impossible to differentiate a default value from a valid parameter value. Nullable tend to be better in this case. – LBushkin May 10 '10 at 16:31
@Bushkin: i totally agree with this! – Simon May 10 '10 at 16:32
thx.. solved my issue with color. +1 – kplshrm7 Nov 26 '15 at 10:17
works like a charm! – oetoni May 26 '21 at 17:38

score 9 · Answer 2 · answered May 10 '10 at 16:29

9

You could check if Color is Color.Empty (which is the default value: default(Color)) or use a nullable value and check for null.

public void log(String msg, Color? c = null) { ... }

answered May 10 '10 at 16:29

Simon

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score 4 · Answer 3 · answered May 10 '10 at 16:35

4

Don't specify the colour. Supply an "error level" instead, and have a mapping between each error level and a colour value. That way 0 and below could be black, then 1 = amber, >2 = red. No need to worry about default values and/or not specifying a value.

answered May 10 '10 at 16:35

Neil Barnwell

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+1 Emphasize the what, not the how. – Bryan Watts May 10 '10 at 16:38
5

Completely disagree - apart from not answering the question, this introduces a new semantic "error level" which then makes this method less useful across different applications (what if I want warnings to be orange in one application and yellow in another). – Justicle Sep 25 '11 at 21:52
@Justicle I see what you're saying, but the actual color should be a presentation concern, and this way the *semantics* are the same in every app, even though the presentation of each app might be different (column in a logfile, colour of a UI element, send an email or don't etc). – Neil Barnwell Aug 25 '15 at 13:41

score 2 · Answer 4 · answered Feb 19 '13 at 15:43

2

Usage suggestion:

public GraphicsLine(Point startPoint, Point endPoint, Color? color = null, double width = 1.0)
{
    StartPoint = startPoint;
    EndPoint = endPoint;
    Color = color ?? Colors.Black;
    Width = width;
}

answered Feb 19 '13 at 15:43

Eric Ouellet

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Color.Black, not Colors.Black – Emanuele Jul 06 '17 at 13:00

C# 4.0: Can I use a Color as an optional parameter with a default value?

4 Answers4