C# 的问题获取和设置列表集合的属性

Question

I need a seperate class where I want to add to some Lists anytime I set a new value. Using _name.Add(value) within the set method doesn't work.

I tried the following

public class XMLInformation
{      
    public String BusType 
    {
        get
        {
            return SubBusType.LastOrDefault();
        }
        set
        {
            SubBusType.Add(value);
        }
    }
    public List<string> SubBusType { get; set; }

}

I use it like this:

        public STARC.GlobalVariables.XMLInformation XMLInformation = new STARC.GlobalVariables.XMLInformation();
        XMLInformation.BusType = "Test";

now i get an error message (sorry error is partly in geeman)

ISSUE

What am I doing wrong?

Answer 1

It can solve your issue. List is not initialized and you are using it. so initialize it first and then use.

public class XMLInformation
{
    public String BusType
    {
        get
        {
            return SubBusType == null ? null: SubBusType.LastOrDefault();
        }
        set
        {
            if (SubBusType == null)
                SubBusType = new List<string>();
            SubBusType.Add(value);
        }
    }
    public List<string> SubBusType { get; set; }
}

Or

public class XMLInformation
{
    public String BusType
    {
        get
        {
            return SubBusType.LastOrDefault();
        }
        set
        {
            SubBusType.Add(value);
        }
    }
            public List<string> SubBusType { get; set; } = new List<string>();
}

Answer 2

You have to Initialize the SubBusType object because at starting it will be null.

You can do either by creating in the constructor like below

 public XMLInformation()
        {
            SubBusType = new List<string>();
        }

or initiate on declaring the SubType itself like below.

public List<string> SubBusType { get; set; } = new List<string>();