使用c＃对象初始化对类成员进行条件初始化

Question

I am having a simple class with 3 not null integer members

public class Test
{
    public int Test1 { get; set; }
    public int Test2 { get; set; }
    public int Test3 { get; set; }
}

Now I want to use something like this

        int? var1 = null;
        int var2 = 2;
        int var3 =5;
       var t =  new Test
        {
            Test1 = var1, // (error) Initialize Test1 only when var1 is not null
            Test2 = var2,
            Test3 = var3
        };

ie I just want to initialize member Test1 only if var1 is not null, so somehow I need to put a check while initialization. I know its a simple question and can be done in diifferent ways but as I am refactoring the existing code and generalizing it, I need solution through Object Initialization only. Looking simple to me but somehow could not able to find solution by myself

Not much experienced programmer, so really appreciate any help

Answer 1

That wouldn't compile anyway, I don't think. But either way the value will get the default value of an int if you don't initialize it. An equivalent would be:

    int? var1 = null;
    int var2 = 2;
    int var3 =5;
    var t =  new Test
    {
        Test1 = var1.GetValueOrDefault(),
        Test2 = var2,
        Test3 = var3
    };

Answer 2

The default value of Test1 is zero so you could use the null-coallescing operator:

var t =  new Test {
    Test1 = var1 ?? 0,
    Test2 = var2,
    Test3 = var3
};

Answer 3

If the class might specify a default besides the default int, or for another reason you need to not call the property setter at all when var1 is null , then you can't use the object initialization syntax for Test1 . (I'm aware that the question says to use object initialization, but just in case that can't work...) Eg

public class Test
{
    public int Test1 { get; set; }
    public int Test2 { get; set; }
    public int Test3 { get; set; }

    public Test()
    {
        Test1 = -1;
    }
}

var t =  new Test
    {
        Test2 = var2,
        Test3 = var3
    };
if (var1 != null) // or (var1.HasValue)
    t.Test1 = var1.Value;

If this isn't the case, you might go with this or any other answer.