C# – string.IsNullOrEmpty(string)’ has some invalid arguments

asp.net-mvc-2c

I converted MVC 3.5 to MVC2 4.0, get an error The best overloaded method match for 'string.IsNullOrEmpty(string)' has some invalid arguments
Here is my code:

<% if (this.Model.VisitId == 0) { %>
        mustSave = true;
    <% } else { %>
        mustSave = false;
    <% } %>
    <% if (String.IsNullOrEmpty(Html.ValidationSummary())) { %>
        dataChanged = false;
    <% } else { %>
        dataChanged = true;
    <% } %>

Thanks in advance

Best Answer

Html.ValidationSummary() returns MvcHtmlString, not a normal string. So, try this:

<% if (MvcHtmlString.IsNullOrEmpty(Html.ValidationSummary())) { %>

Related Solutions

C# – the difference between String and string in C#

string is an alias in C# for System.String.
So technically, there is no difference. It's like int vs. System.Int32.

As far as guidelines, it's generally recommended to use string any time you're referring to an object.

e.g.

string place = "world";

Likewise, I think it's generally recommended to use String if you need to refer specifically to the class.

e.g.

string greet = String.Format("Hello {0}!", place);

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – Case insensitive ‘Contains(string)’

You could use the String.IndexOf Method and pass StringComparison.OrdinalIgnoreCase as the type of search to use:

string title = "STRING";
bool contains = title.IndexOf("string", StringComparison.OrdinalIgnoreCase) >= 0;

Even better is defining a new extension method for string:

public static class StringExtensions
{
    public static bool Contains(this string source, string toCheck, StringComparison comp)
    {
        return source?.IndexOf(toCheck, comp) >= 0;
    }
}

Note, that null propagation ?. is available since C# 6.0 (VS 2015), for older versions use

if (source == null) return false;
return source.IndexOf(toCheck, comp) >= 0;

USAGE:

string title = "STRING";
bool contains = title.Contains("string", StringComparison.OrdinalIgnoreCase);

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – Case insensitive ‘Contains(string)’

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