Why behavior of NameValueCollection is different?

Question

NameValueCollection x = new NameValueCollection(Request.QueryString);
string x1 = x.ToString();
NameValueCollection y = HttpUtility.ParseQueryString(Request.QueryString.ToString());
string y1 = y.ToString();

when I execute above code, value of x1 and y1 become

x1="System.Collections.Specialized.NameValueCollection"
y1="abc=1&xyz=2"   //url pass to controller is 'localhost/first/getresult/?abc=1&xyz=2'

I don't understand why the value of x1 and y1 is different. I checked the documentation of ParseQueryString() and it show that it return NameValueCollection and I don't get any other information.

So, I don't understand why behavior is different of x and y.

Answer 1

In case of HttpUtility.ParseQueryString an instance of the class HttpValueCollection is returned(source) which inherits from NameValueCollection. Obviously this classs overrides ToString meaningfully as opposed to NameValueCollection which inherits ToString from object, hence just diplays the full-type name.

That's not mentioned in ParseQueryString because HttpValueCollection is internal. They don't want you to use this type and you should not rely on this type being returned.

Here's the source of ToString in HttpValueCollection:

public override String ToString() {
    return ToString(true);
}

internal virtual String ToString(bool urlencoded) {
    return ToString(urlencoded, null);
}

internal virtual String ToString(bool urlencoded, IDictionary excludeKeys) {
    int n = Count;
    if (n == 0)
        return String.Empty;

    StringBuilder s = new StringBuilder();
    String key, keyPrefix, item;
    bool ignoreViewStateKeys = (excludeKeys != null && excludeKeys[Page.ViewStateFieldPrefixID] != null);

    for (int i = 0; i < n; i++) {
        key = GetKey(i);

        // Review: improve this... Special case hack for __VIEWSTATE#
        if (ignoreViewStateKeys && key != null && key.StartsWith(Page.ViewStateFieldPrefixID, StringComparison.Ordinal)) continue;
        if (excludeKeys != null && key != null && excludeKeys[key] != null)
            continue;
        if (urlencoded)
            key = UrlEncodeForToString(key);
        keyPrefix = (key != null) ? (key + "=") : String.Empty;

        string[] values = GetValues(i);

        if (s.Length > 0)
            s.Append('&');

        if (values == null || values.Length == 0) {
            s.Append(keyPrefix);
        }
        else if (values.Length == 1) {
            s.Append(keyPrefix);
            item = values[0];
            if (urlencoded)
                item = UrlEncodeForToString(item);
            s.Append(item);
        }
        else {
            for (int j = 0; j < values.Length; j++) {
                if (j > 0)
                    s.Append('&');
                s.Append(keyPrefix);
                item = values[j];
                if (urlencoded)
                    item = UrlEncodeForToString(item);
                s.Append(item);
            }
        }
    }

    return s.ToString();
}