C# 3.0 How can I get readonly property value?

Question

In C# 3.0, I'm doing the code below to declare a DateTime property and a int age property that is read only.

public class MyClass{
    public DateTime dateOfBirth{ get; set; }
    public int age { get; }

    public MyClass(){}

    public int CalculateAge(){}
}

But how can I get this updated age (that it's read only) when someone enters his date of birth in a form, for example?

I didn't even know that it was possible to declare an auto-implemented property without a set-block (private would be fine) since you can never initialize the property. — Cecil Has a Name, Sep 03 '09 at 19:39
It's not possible to do this - the compiler will complain, precisely for the reason you give. — Pavel Minaev, Sep 03 '09 at 19:40

score 8 · Answer 1 · answered Sep 03 '09 at 19:39

8

You need to implement the "age" property so it works off the dateOfBirth property:

public int age { 
    get {
         return (DateTime.Now - this.dateOfBirth).Days / 365;
    }
}

answered Sep 03 '09 at 19:39

Reed Copsey

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1

yeah - well, I was just trying to show the technique, not the specifics. – Reed Copsey Sep 03 '09 at 20:28

score 7 · Accepted Answer · answered Sep 03 '09 at 19:38

7

Don't store the age, instead calculate it when get of the age property is executed:

public int Age { get { return 100; } }

But instead of returning 100, you do the calculation.

answered Sep 03 '09 at 19:38

Svante Svenson

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I've tried to do that but in my CalculateAge method it says that Age cannot be assigned because it's read only. – André Miranda Sep 03 '09 at 19:41
4

He said 'don't store the age...' – n8wrl Sep 03 '09 at 19:45

score 2 · Answer 3 · answered Sep 03 '09 at 19:39

You can't use an auto readonly property for this. You'll have to implement the property. You might also consider using a TimeSpan instead of int, since it will be more versatile.

public TimeSpan Age 
{ 
    get 
    { 
        return DateTime.Now - this.dateOfBirth; 
    } 
}

score 2 · Answer 4 · answered Sep 03 '09 at 19:42

Instead of having Age be an automatic property, implement an age calculator.

public class MyClass {
    public DateTime DateOfBirth { get; set; }
    public int Age { 
        get {
            DateTime now = DateTime.Now;
            int age = now.Year - DateOfBirth.Year;
            if(now < DateOfBirth.AddYears(age)) age--;
            return age;
        }
    }
}

You should probably refactor the above calculation out into a method, but the above demonstrates the salient point.

score 1 · Answer 5 · edited May 23 '17 at 10:33

1

As Svinto says, calculate the age and return that in the get method of your Age property. See How do I calculate someone's age in C#? on SO for ideas on how to do this.

edited May 23 '17 at 10:33

Community

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answered Sep 03 '09 at 19:42

Dan Diplo

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score 1 · Answer 6 · answered Sep 03 '09 at 19:47

1

In case you want a property which only you can assign, but which anyone can read:

public class MyClass
{
    public int Age { get; private set; }
}

Then your class can assign Age, but other classes can only read it.

answered Sep 03 '09 at 19:47

Ben M

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score 0 · Answer 7 · answered Sep 03 '09 at 19:38

0

Put your code to calculate the age in your age property.

For example:

public int Age
{
     get
     {
          return (age code here);
     }
}

answered Sep 03 '09 at 19:38

that won't compile. You can't implicitly convert a timespan to an int. – Reed Copsey Sep 03 '09 at 19:39
@Reed Copsey - there is no timespan in dark's code; it just says 'age code here' in the return. the actual code for computing the integer age value goes in the parantheses. – JeremyDWill Sep 03 '09 at 19:44

score 0 · Answer 8 · answered Sep 03 '09 at 19:40

0

Why not change your implementation a little:

public class MyClass
{
    public DateTime DateOfBirth {get; set;}
    public int Age
    {
        get
        {
            return this.CalculateAge();
        }
    }
}

answered Sep 03 '09 at 19:40

Justin Niessner

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C# 3.0 How can I get readonly property value?

8 Answers8