为什么.NET在错误的IF语句上执行代码？

Question

I have following code:

var dateFrom = DateTime.Parse(string.Format(string.Format("01.04.{0}", dateProperty.Value.AddYears(-1).Year))
if (object.nullablebool.HasValue ? object.nullablebool.Value : false  
&& (string == "V" || string == "N")
&& someDate.HasValue && object.SomeOtherDate.HasValue 
&& someDate.Value.Date > dateFrom.Date)
{
       >> Code
}

I have tested adding .Date or even specifiing exact year from the DateTime struct, but nothing worked.

When executing the code, even if

someDate.Value.Date > dateFrom.Date

equals 1700 > 2018, the code executed as if it was true, even though the debugger says it´s false.

When I removed this part from the condition, following code:

someDate.HasValue && object.SomeOtherDate.HasValue

When I made someDate null, so someDate.HasValue is false, the if statement still executes as true.

What did it fix? Taking these two conditions to another if:

var dateFrom = DateTime.Parse(string.Format(string.Format("01.04.{0}", dateProperty.Value.AddYears(-1).Year))
if (object.nullablebool.HasValue ? object.nullablebool.Value : false  
&& (string == "V" || string == "N"))    
{
     if (someDate.HasValue && object.SomeOtherDate.HasValue 
     && someDate.Value.Date > dateFrom.Date)
     {
          >> Code
     }
     else 
     {
          >> Code 
     }           
}

The code works, but it´s way too ugly. I'm running on Visual Studio 2017 Pro. Any ideas why it behaves like that? Executing false statements? Thanks

Answer 1

Your if statement performs different then expected, because it is parsed different as you wouls expect. object.nullablebool.HasValue ? object.nullablebool.Value : false && ... object.nullablebool.HasValue ? object.nullablebool.Value : false && ... is parsed as object.nullablebool.HasValue ? object.nullablebool.Value : (false && ...) object.nullablebool.HasValue ? object.nullablebool.Value : (false && ...) . So if object.nullablebool has a value, thats the result of the condition. To fix this you have to add parenthesis like this:

if ((object.nullablebool.HasValue ? object.nullablebool.Value : false )
&& (string == "V" || string == "N") 
&& someDate.HasValue && object.SomeOtherDate.HasValue 
&& someDate.Value.Date > dateFrom.Date)
{
     // if body
}

Answer 2

Let's brush up your code (please, get rid of names like string , object ; change them into meanful names):

  // You don't want any formatting but a simple constructor
  var dateFrom = new DateTime(dateProperty.Value.Year - 1, 4, 1);    

  // object.nullablebool == true - if object.nullablebool has value and the value is true
  if (object.nullablebool == true && (string == "V" || string == "N")) {
    // if someDate.Value is null the result will be false 
    // All we have to do is to propagate the null: ?. in someDate?.Date
    if (someDate?.Date > dateFrom.Date && object.SomeOtherDate.HasValue) {
      // Code
    }
    else {  
      // Code
    }
  }