Class constructor in Web API

Question

Ive been researching and I am a little stuck on finding the right answer.

Lets say I have a c# class with auto properties. I want to have some of these properties calculated based of the properties that a user will change. I understand that you can use a constructor to do this calculation on creation of a new object.

What I am trying to find out is, in a web api does the class constructor get called on an update? Do i do the following or create customer setters?

eg

class myclass 
{
    public int Num1 { get; set; }
    public int Num2 { get; set; }
    public int Num3 { get; set; }
    public int Num4 { get; set; }

    //these get changed when values above get changed by API
    public int result1 { get; set; } 
    public int result2 { get; set; }
    public int result3 { get; set; } 

    //constructor
    public myClass()
    {
        result1 = Num1 + Num2;
        result2 = Num3 + Num2;
        result3 = Num4 + Num2;
    {
}

probably you can use INotifyPropertyChanged (reference: learn.microsoft.com/en-us/dotnet/api/…) — Kien Chu
– Kien Chu, Commented Nov 12, 2018 at 1:46
Once the Class is construted, the constructor never runs Again. To set properties afterwards, simply do: Num1 = whatever; — Poul Bak
– Poul Bak, Commented Nov 12, 2018 at 1:46
What you considered changing result1 to be a read-only property? — mjwills
– mjwills, Commented Nov 12, 2018 at 2:17

jazb · Accepted Answer · 2018-11-12 02:53:34Z

1

if I understand correctly, you simply need some derived readonly properties:

class myclass
{
    public myclass()
    {

    }

    public int Num1 { get; set; }
    public int Num2 { get; set; }
    public int Num3 { get; set; }
    public int Num4 { get; set; }


    public int result1 => Num1 + Num2;
    public int result2 => Num3 + Num2;
    public int result3 => Num4 + Num2;

}

answered Nov 12, 2018 at 2:53

jazb

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Comments

Kien Chu · Accepted Answer · 2018-11-12 02:05:04Z

What you need to use is INotifyPropertyChanged, see the minimal example below

void Main()
{
    var test = new myClass();
    test.Num1 = 1;
    test.Num2 = 2;
    test.Num3 = 3;
    test.Num4 = 4;

    test.result1.Should().Be(3);
    test.result2.Should().Be(5);
    test.result3.Should().Be(6);

    test.Num1 = 2;
    test.result1.Should().Be(4);
    test.Num2 = 0;
    test.result2.Should().Be(3);
    test.result3.Should().Be(4);
}

class myClass : INotifyPropertyChanged
{
    // private setter since these values are only being set when the num{i} are updated
    public int result1 { get; private set; }
    public int result2 { get; private set; }
    public int result3 { get; private set; }

    public event PropertyChangedEventHandler PropertyChanged;
    public myClass()
    {
        PropertyChanged += new PropertyChangedEventHandler(UpdateResultValue);
    }

    private void UpdateResultValue(object sender, PropertyChangedEventArgs e)
    {
        result1 = num1 + num2;
        result2 = num2 + num3;
        result3 = num2 + num4;
    }

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    protected bool SetField<T>(ref T field, T value, [CallerMemberName] string propertyName = null)
    {
        if (EqualityComparer<T>.Default.Equals(field, value)) return false;
        field = value;
        OnPropertyChanged(propertyName);
        return true;
    }

    private int num1;
    public int Num1
    {
        get => num1;
        set => SetField(ref num1, value);
    }

    private int num2;
    public int Num2
    {
        get => num2;
        set => SetField(ref num2, value);
    }

    private int num3;
    public int Num3
    {
        get => num3;
        set => SetField(ref num3, value);
    }

    private int num4;
    public int Num4
    {
        get => num4;
        set => SetField(ref num4, value);
    }
}

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