项目之间的类中的对象持久性

Question

I know I shouldn't have to ask this but whatever it is I am missing is driving me nuts! I have done this many times before and I can only put it down to old age and slight senility.

I have a class with two objects that get initialized in the constructor...

public class EbayFunctions
{
    private static ApiContext apiContext = null;
    private static List<StoreCategoriesFlattened> storeCategories =  new List<StoreCategoriesFlattened>();

    public EbayFunctions()
    {
        ApiContext apiContext = GetApiContext();
        List<StoreCategoriesFlattened> storeCategories = GetFlattenedStoreCategories();
    }
    public string GetStoreCategoryIdForItem(string category)
    {
       var result = storeCategories.Find(x => x.CCDatabaseMatch == category);
       return ""; //Ignore will return a value
    }
}

then I have a forms app (test harness) that makes use of the class and on button click I call a method...

namespace EbayTestHarness
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void cmdGetEbayStoreCatID_Click(object sender, EventArgs e)
        {
            EbayFunctions ebf = new EbayFunctions();
            string ddd = ebf.GetStoreCategoryIdForItem("Motors > Bikes");

        }
    }
}

However apiContext persists between calls but storeCategories gets populated on EbayFunctions ebf = new EbayFunctions(); and is null when string ddd = ebf.GetStoreCategoryIdForItem("Motors > Bikes"); is called.

I know its something stupid but what am I missing?

Answer 1

Your problem is here:

private static ApiContext apiContext = null;
private static List<StoreCategoriesFlattened> storeCategories =  new List<StoreCategoriesFlattened>();

public EbayFunctions()
{
    ApiContext apiContext = GetApiContext();  // local!!
    List<StoreCategoriesFlattened> storeCategories = GetFlattenedStoreCategories();  // local!!
}

You're not setting the static fields - you're introducing local variables that then go out of scope and are (eventually) garbage collected. Take out the type indicators to set the static fields:

public EbayFunctions()
{
    apiContext = GetApiContext();
    storeCategories = GetFlattenedStoreCategories();
}

Also, as @PatrickHofman points out, the initialization of static members should be done once - preferably in a static constructor:

static EbayFunctions()
{
    apiContext = GetApiContext();
    storeCategories = GetFlattenedStoreCategories();
}