Question

Let’s say I have a configuration property that looks like this. Note that there is no default value.

[ConfigurationProperty("x", IsRequired = true)]
[StringValidator(MinLength = 1)]
public string X
{
    get { return (string)this["x"]; }
    set { this["x"] = value; }
}

Now I add my section like this:

<mySection x="123" />

I’ll get this error:

The value for the property ‘x’ is not
valid. The error is: The string must
be at least 1 characters long.

It works if I change the configuration property to include a default like this:

[ConfigurationProperty("x", DefaultValue="abc", IsRequired = true)]
[StringValidator(MinLength = 1)]
public string X
{
    get { return (string)this["x"]; }
    set { this["x"] = value; }
}

This implies that validator validates the default value even if IsRequired is true. It also means that I have to include a dummy default values on all my properties to pass validation even though they won’t actually be used.

Is this just bad design or is there a valid reason for this behavior?

Answer 1

I have had this problem before. There was a valid reason for this but I cannot remember the details.

I cannot remember if this works but you can try declaring the property in the constructor where null is the default value.

public class CustomConfigurationSection : ConfigurationSection
{
    public CustomConfigurationSection()
    {
        Properties.Add(new ConfigurationProperty(
            "x",
            typeof(string),
            null,
            null,
            new StringValidator(1),
            ConfigurationPropertyOptions.IsRequired));
    }


    public string X
    {
        get { return (string)this["x"]; }
        set { this["x"] = value; }
    }
}

This is related to using default values and validators but is where a default value is wanted.
http://msdn.microsoft.com/en-us/library/system.configuration.configurationproperty(VS.85).aspx#1

EDIT

I have just tried out the previous code and it does as I expected. My previous code did not compile as I missed out a constructor property so I have fixed that.