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Answer 1

+3 A:

Those expressions are invalid in C# because the .NET || and && operators are strongly typed.

There is, however, the x ?? y operator which returns y if x is null and x otherwise:

string value1;
string value2 = "default value";

value1 = Request.Form["valueA"] ?? Request.Form["valueB"] ?? value2;
                                ^                         ^

dtb 2009-08-28 14:17:37

+1. But what happens if the url contains "?valueA=)

AnthonyWJones 2009-08-28 14:32:30

@Anthony Nothing will happen a string "" does not affect the ?? nor and variables

Jonathan Shepherd 2009-08-28 14:41:27

EDIT: and = any

Jonathan Shepherd 2009-08-28 14:42:03

stevemegson 2009-08-28 15:01:04

@Jonathan: Just to clarify: valueA ?? valueB where valueA = "" results in "" regardless of the value of valueB. This may or may not be desirable.

AnthonyWJones 2009-08-28 15:01:09

@Jonathan: BTW, if you want to make a correction to a comment rather than adding another comment containing errata, copy'n'paste the original comment text into a new comment, correct it and add it. Then hover over your original comment and click the little delete icon.

AnthonyWJones 2009-08-28 15:03:27

Answer 2

+1 A:

If I understand your "question" correctly you need to understand that C# handles type in much stricter manner. Null is not treated as false, in fact the only type you can use in a boolean expression is a boolean, unlike javascript which will accept any type into a boolean expression and make some reasonable guess about what is meant.

The only operator that gets close to what you are doing in Javascript is ?? :-

 var r1 = (null ?? "1º" ?? "2º") // Results in 1º
 var r2 = (null ?? null ?? "2º") // Results in 2º

However this doesn't work:-

 var r1 = (null ?? 1 ?? 2)  //Compile error

Integers are value types and cannot be null.

Solution to Edit

Whenever there is the slightest hint of "processing" of querystring/form values before use I would tuck it all away inside a property. (In fact I tend to place all such access in a property even if its just {return Request.QueryString["stuff"]; }).

 string _Value;
 public string Value
 {
    get
    {
       if (_Value == null)
       {
         _Value = CoalesceNullOrEmpty(Request.Form["valueA"],
           Request.Form["valueB"],
           "Default Value");
         }
       }
       return _Value;
    }
 }

//Can place this in the page but is more useful in a utility dll
public string CoalesceNullOrEmpty(params string[] values)
{
  foreach(string value in values)
    if (!String.IsNullOrEmpty(value))
      return value;

  return null;
}

Now use the Value property where you would have used the the value1 property.

AnthonyWJones 2009-08-28 14:22:54

Answer 3

A:

If you want a series of bools, why not write a class that converts for you, applying the rules you want. If your rules are "if it's null, it's false; if it's non-null it's the boolean value, otherwise it's true" then this method will work for you.

static List<bool> ToBool(FormCollection form) { // couldn't find the type on MSDN
    List<bool> result = new List<Bool>();
    foreach (object o in form) {
         if (o == null) {
             result.Add(false);
         }
         else {
             if (o is bool) {
                 result.Add((bool)o);
             }
             else {
                // do whatever other conversion
                result.Add(true); // probably the wrong thing - depends on what you're testing
             }
         }
     }
     return result;
}

plinth 2009-08-28 14:37:16

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