I'm relatively new/inexperienced to c# and I am trying to write a bool method to validate if the user input in a windows form is empty, which returns as true or false, as well as change the errorMessage Variable to have new text if it returns false.

 public static bool IsPresent(string value)
 { 
     if (value == "")
     {
         errorMessage = "all textboxes and combo boxes must be filled";
         return false;
     }
     else
     {
         errorMessage = "";
         return true;
     }
}

I get compile time error on errorMessage, saying

"An object reference is required for the nonstatic field, method, or property 'member'".

I declared the errorMessage variable at the top of my file and made it public. I have tried getting rid of the static aspect of the method, which does fix it, but causes more errors elsewhere in my code. Do you know how I can go about fixing this?

CodePudding user response：

You can declare public static field and do it like this of course:

static class Helper
{
    public static string errorMessage;

    public static bool IsPresent(string value)
    {
        if (value == "")
        {
            errorMessage = "all textboxes and combo boxes must be filled";
            return false;
        }

        else
        {
            errorMessage = "";
            return true;
        }
    }
}

But this's got a few problems, one of them is that errorMessage can be now modified by some foreign class, so it should be changed to something else, for example:

private static string errorMessage;

public static string GetMessageCopy()
{
    return errorMessage;
}

You can change this to property, which does the same thing, but it's easier to read:

public static string ErrorMessage { get; private set; } // property should always start with a big letter

Now only Helper class can modify ErrorMessage, but everyone can read it.

Next problem is that name of your parameter "value" is a C# keyword, which is used for different things, so please, think of renaming it.

CodePudding user response：

You need to declare variable first inside the static function. If you have declared it outside the method's scope I recommend removing the static keyword so it should look like this:

string errorMessage;
bool IsPresent(string value)
{
    if (value == "")
     {
          errorMessage = "all textboxes and combo boxes must be filled";
          return false;
     }
     else
     {
         errorMessage = "all textboxes and combo boxes must be filled";
         return true;
     }
}

CodePudding user response：

You should read up on static. You could start with static (C# Reference).

However, there are solutions that don't require a member variable (what you called at the top of my file) and avoid the static/non-static issue. For example, let's consider this solution:

(bool IsValid, string? ErrorMessage) IsPresent(string? s)
{
     if (string.IsNullOrEmpty(s))
     {
          return(IsValid: false, ErrorMessage: "All textboxes and combo boxes must be filled");
     }
     else
     {
         return(IsValid: true, ErrorMessage: null);
     }
}

Notes:

1. Please note I used string.IsNullOrEmpty rather than == "". You may want to use string.IsNullOrWhiteSpace to make the requirement even stronger.

2. You may need to change (bool IsValid, string? ErrorMessage) IsPresent(string? s) to (bool IsValid, string ErrorMessage) IsPresent(string s) if you're not using a fresh version of .NET.

If we think about a bit more we can notice that IsValid is redundant. Checking if the error is return is enough:

string? CheckValid(string? s)
{
     if (string.IsNullOrWhiteSpace(s))
     {
          return "All textboxes and combo boxes must be filled";
     }

     //if ( ... some other requirement )
     //{
     //     return "Some error";
     //}

     return null;
}