3

I have this class:

public class CalendarData_Day
{
    public DateTime Date { get; set; }
    public DayType TypeOfDay { get; set; }
    public bool Choose { get; set; }

    public CalendarData_Day(DateTime datum) : this(datum, DayType.Normal, true)
    {
    }

    public CalendarData_Day(DateTime datum, DayType typDne) : this(datum, typDne, true)
    {
    }

    public CalendarData_Day(DateTime datum, DayType typDne, bool vybran)
    {
        this.Date = datum;
        this.TypeOfDay = typDne;
        this.Choose = vybran;
    }
}

and I want in second constructor check if DayType is Weekend and if it is then not send to Choose true but false. Anybody knows how can I do it? I know I can add to last constructor if and checked but it doesn´t seem right for me. I think there is better way I think that I should do it other way or is this in last contructor okay:

if (TypeOfDay == DayType.Weekend)
    this.Choose = false;

I know it´s working but I don´t know it is right way.

Edit: I am sorry for that I don´t explained everything. There is more than 2 DayTypes, lets say there is Holiday, Work, ... And I want that user can call class with just second constructor and if DayType would be Weekend or Holiday then Choose must be false but if it would be Normal or Work it should be true or user must user last contructor and set DayType to Work and Choose to false. It is complicated I am sorry I should wrote this first time.

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3 Answers 3

Reset to default
7

It would be nicer to pass the chained constructor argument based on the parameter:

public CalendarData_Day(DateTime datum, DayType typDne)
    : this(datum, typDne, typeDne != DayType.Weekend)
{        
}

That way you don't need to set the property twice - once to a sort of default value and then fix it based on information you already knew.

I would personally change the parameter name from typDne to dayType or something similar.

EDIT: I've only just seen that you were considering putting your test into the last constructor rather than the second one. I would expect the value given by the caller for vybran to be accepted as-is, rather than conditionally ignored. You only describe wanting the second constructor to check for DayType == Weekend - not the last constructor - so it's only the second constructor that should change.

EDIT: If Choose must be false for Weekend or Holiday then I would enforce that in the last constructor but pick the value in the second constructor:

public CalendarData_Day(DateTime datum, DayType typDne)
    : this(datum, typDne,
           typeDne != DayType.Weekend && typeDne != DayType.Holiday)
{        
}

public CalendarData_Day(DateTime datum, DayType typDne, bool vybran)
{
    if (vybran && (typeDne == DayType.Weekend || typeDne == DayType.Holiday))
    {
        throw new ArgumentException(
           "vybran cannot be true for holiday or weekend dates", "vybran");
    }
    this.Date = datum;
    this.TypeOfDay = typDne;
    this.Choose = vybran;
}
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4 Comments

I like your solution but I am sorry I forget mention that it is no just DayType.Weekend and Normal, it could be more types so I think I must set property twice in last constructor.
@Bibo: Why? My method does exactly what you've described - Choose will be false if typeDne is Weekend and true otherwise... and again, why would you want to override what the user had passed in if they called the last constructor directly? If that really is your intention, please edit your question to clarify it. Think about what should happen if the user directly calls new CalendarData_Day(date, DayType.Weekend, true)
Weekend should be always false but you are right that it can do mess in some cases so I edit my post.
@Bibo: I've edited my answer - see the second part. Note the separation of "picking a default value" from "enforcing validity of values".
4

Validating parameters in your constructor is perfectly OK.

Though you should ensure that if the condition is false your code still works as expected:

if (TypeOfDay == DayType.Weekend)
{
   this.Choose = false;
}
else
{
   this.Choose = vybran;
}

You may consider throwing an ArgumentException if the parameters passed in are completely wrong.

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4 Comments

Normally when I see an "if" where all that's changing in the two bodies is the value used in the same way, I use a conditional or some other expression which will give the right answer. In this case: this.Choose = TypeOfDay != DayType.Weekend;. Use parentheses if you want to make the comparison clearer.
@Jon - Agreed, unless you want the actual passed in value if the test fails. Your version and mine do different things.
Ooh, I'd actually misread the question - I'd thought that test was in the second constructor... although the description only talks about the behaviour changing when the second constructor is called. Odd. Have edited my answer to highlight this.
@Oded: :) I only 15 minutes before the weekend starts. That's my excuse!
0

If you have very extensive logic in one of your constructors you might benefit from static construction functions calling private constructors.

class MyClass
{
  private MyClass(...)
  {

  }
  public static MyClass CreateMyClassWithValidation(...)
  {
    if(....)
      return new MyClass(...);
  } 
}
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