C#列表<T> .NET 2.0 中的 .ConvertAll

Question

I have a list of strings. All of the strings have whitespace that needs to be converted to underscores. I am fully capable of using a for or foreach loop to do this. I am still relatively new to C# and would like to become more familiar with it. With that said, my question is:

How can I get the following code to work in .NET 2.0? When I check fieldList at the end of the ConvertAll operation, nothing has changed. Is there an issue with passing the string by value instead of reference?

string fields =
  "First Name,Middle Name,Last Name,Birth Date,Gender,Address,City,State,Zip,Email";
List<string> fieldList = new List<string>(fields.Split(','));
fieldList.ConvertAll<string>(new Converter<string, string>(
    delegate(string str)
    {
        str = str.Trim();
        str = str.Replace(' ', '_');
        return str;
    }
));

Please, keep in mind, that I am using .NET 2.0 and cannot currently switch, so I do not have the luxury of using LINQ or Lambdas.

Answer 1

You need to assign the results of the ConvertAll method to the variable like this:

fieldList = fieldList.ConvertAll<string>(new Converter<string, string>(
    delegate(string str)
    {
        str = str.Trim();
        str = str.Replace(' ', '_');
        return str;
    }
));

The ConvertAll method returns a new List<T> so you need to assign the result of the method. If you want to re-use the fieldList variable you can but it may be better to create a new variable to improve the clarity of your code:

List<String> convertedFieldList 
    = fieldList.ConvertAll<string>(new Converter<string, string>(
        delegate(string str)
        {
            str = str.Trim();
            str = str.Replace(' ', '_');
            return str;
        }
));

As Marc Gravell points out in a comment below, you can simplify the syntax of this expression by doing this:

List<String> convertedFieldList 
    = fieldList.ConvertAll<String>(delegate(String str) {
            return str.Trim().Replace(' ', '_');
        });

Answer 2

ConvertAll doesn't change the input list. It returns a new list containing the converted stuff. By the way, you can remove the new Converter<string,string> with C# 2.0+:

List<string> converted = fieldList.ConvertAll<string>
    (delegate(string s) { return s.Trim().Replace(' ', '_'); });

Besides, nothing prevents you from using a C# 3.0 compiler and LINQBridge and target .NET 2.0.