Automatic Property Values and Defaults

Question

Possible Duplicate:
How do you give a C# Auto-Property a default value?

I have a property in a class like so

public String fontWeight { get; set; }

I want it's default to be of "Normal"

Is there a way to do this in "automatic" style rather than the following

public String fontWeight {
    get { return fontWeight; } 
    set { if (value!=null) { fontWeight = value; } else { fontWeight = "Normal"; } }
}

Who is assigned Normal as default? – sll Aug 15 '11 at 10:32 — sll, Aug 15 '11 at 10:32

score 13 · Answer 1 · answered Aug 15 '11 at 10:48

13

Yes you can.

If your looking for something like:

[DefaultValue("Normal")]
public String FontWeight
{
    get;
    set;
}

Do a google search for 'Aspect Oriented Programming using .NET'

..if this is overkill for you do this:

private string fontWeight;
public String FontWeight {
    get
    {
        return fontWeight ?? "Normal";
    }
    set {fontWeight = value;} 
}

answered Aug 15 '11 at 10:48

Lee Smith

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so this as auto as you can get? cool – Joseph Le Brech Aug 15 '11 at 10:49
The `DefaultValueAttribute` is only recognized by some visual designers. I think the OP wanted to initialize the property value upon construction or access of any caller. – Shimmy Weitzhandler Feb 16 '17 at 02:42

Guffa · Accepted Answer · 2011-08-15T11:15:18.840

10

No, an automatic property is just a plain getter and/or setter and a backing variable. If you want to put any kind of logic in the property, you have to use the regular property syntax.

You can use the ?? operator to make it a bit shorter, though:

private string _fontWeight;

public String FontWeight {
  get { return _fontWeight; } 
  set { _fontWeight = value ?? "Normal"; }
}

Note that the setter is not used to initialise the property, so if you don't set the value in the constructor (or assign a value in the variable declaration), the default value is still null. You could make the check in the getter instead to get around this:

private string _fontWeight;

public String FontWeight {
  get { return _fontWeight ?? "Normal"; } 
  set { _fontWeight = value; }
}

edited Aug 15 '11 at 11:15

answered Aug 15 '11 at 10:33

Guffa

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Nice one. Keep forgetting about the ??. – Jethro Aug 15 '11 at 10:41
I see where you are getting at, the set wont run and set anything to normal if it's not set at all. the null needs to be checked on get :) – Joseph Le Brech Aug 15 '11 at 10:44
i'm accepting this, but i did need a backing field like @Jethro said – Joseph Le Brech Aug 15 '11 at 10:49
@Joseph Le Brech: Yes, there is no automatic member variable for a regular property, which I assumed that you just left out of your example. I added it to the code examples so that it is clear for anyone who sees this. :) – Guffa Aug 15 '11 at 11:17
Looks good, thanks. – konbernu Apr 16 '19 at 10:34

score 2 · Answer 3 · answered Aug 15 '11 at 10:32

2

You will need to use a backing field.

private string fontWeight;
public String FontWeight 
{ 
    get { String.IsNullOrEmpty(fontWeight) ? "Normal" : fontWeight;}
    set {fontWeight = String.IsNullOrEmpty(value) ? "Normal" : value;} 
}

answered Aug 15 '11 at 10:32

Jethro

5,896
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score 2 · Answer 4 · answered Aug 15 '11 at 10:42

You either need to use a backing field and initialize that to your default value

private String fontWeight = "Normal";
public String FontWeight
{
    get { return fontWeight; }
    set { fontWeight = value; }
}

or, keep the auto property and call the setter in your constructor

public constructor()
{
    FontWeight = "Normal";
}

public String FontWeight { get; set; }

score 1 · Answer 5 · edited May 23 '17 at 12:31

1

One way to do it is using PostSharp as detailed in this answer to a similar question.

edited May 23 '17 at 12:31

Community

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answered Aug 15 '11 at 10:36

Jens

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score 1 · Answer 6 · answered Aug 15 '11 at 10:44

You could use the DefaultValue attribute:

    [DefaultValue("Normal")]
    public string FontWeight { get; set; }

Although it notes that

A DefaultValueAttribute will not cause a member to be automatically initialized with the attribute's value. You must set the initial value in your code.

so you could use this in conjunction with initialisation in the constructor or via a backing field and default handling.

score 0 · Answer 7 · answered Aug 15 '11 at 10:37

You'd need either a variable like so:

string fontWeight;

public string FontWeight
{ 
    get
    {
        if (string.IsNullOrEmpty(fontWeight))
            fontWeight = "Normal";

        return fontWeight;
    }
    set { fontWeight = value; } 
}

Or use a Constructer to set an initial value:

class FontClass
{
    public string FontWeight { get; set; }

    public FontClass()
    {
        FontWeight = "Normal";
    }
}

Automatic Property Values and Defaults

7 Answers7