Question

I have a question about naming SharedSizeGroups in WPF grids mostly out of curiosity. I noticed on MSDN that they list restrictions for the group’s string name:

The SharedSizeGroup property value must satisfy the following rules:

• Must not be empty.
• Must only consist of letters, digits, and underscore characters.
• Must not start with a numeric value.

I have some groups that I named numerically ("1", "2", "3", etc.) and have never had a problem with them. Just for kicks I renamed some groups to something like ",-[]" and they still worked too. So these rules are not enforced and seemingly not necessary. Does anybody know the reason for the rules in the documentation? Is it possible for the names to conflict with something that WPF is doing internally?

Edit: Okay, so WPF does enforce it after all, validation just doesn’t fire in my non-compiled templates.

Answer 1

Interesting, I took a look at the DefinitionBase class in reflector and the SharedSizeGroup property.

It creates a dependency property with a validation callback defined as the following:

SharedSizeGroupProperty = DependencyProperty.Register("SharedSizeGroup", typeof(string), typeof(DefinitionBase), new FrameworkPropertyMetadata(new PropertyChangedCallback(DefinitionBase.OnSharedSizeGroupPropertyChanged)), new ValidateValueCallback(DefinitionBase.SharedSizeGroupPropertyValueValid));


private static bool SharedSizeGroupPropertyValueValid(object value)
    {
        if (value == null)
        {
            return true;
        }
        string str = (string)value;
        if (str != string.Empty)
        {
            int num = -1;
            while (++num < str.Length)
            {
                bool flag = char.IsDigit(str[num]);
                if (((num == 0) && flag) || ((!flag && !char.IsLetter(str[num])) && ('_' != str[num])))
                {
                    break;
                }
            }
            if (num == str.Length)
            {
                return true;
            }
        }
        return false;
    }

I tested this, and it does in fact return false for anything containing non-numeric, non-alpha, non-underscore characters. It also returns false for any group starting with a number. So it seems to follow general variable name rules..

My guess is this would most likely throw some sort of exception, but perhaps it is being handled. Have you checked the output window?

I tried an invalid name, and I got an XAMLParseException.