c# - AsyncCallback 传递参数

Question

我想通过List<items>进入AsyncCallback在函数中 LoadHistoryAsync(List<int> Items)但是result.AsyncState在 CallForNewData(IAsyncResult result)为什么为空？

namespace ConsoleApplication3
{
class Program
{
    static void Main(string[] args)
    {
        List<int> Items = new List<int>();
        Data D = new Data();
        D.LoadHistoryAsync(Items);
        //D.LoadNewPointsAsync(Items);
        Console.ReadKey();
    }
}
public class Data
{
    public void LoadHistoryAsync(List<int> Items)
    {
        Action<List<int>> GetHistoryInformation = new Action<List<int>>(GetHistory);
        //IAsyncResult History = GetHistoryInformation.BeginInvoke(Items, null, null);
        IAsyncResult History = GetHistoryInformation.BeginInvoke(Items, new AsyncCallback(CallForNewData), null);
    }

    public void GetHistory(List<int> Items)
    {
        Random rnd = new Random();
        System.Threading.Thread.Sleep(rnd.Next(1,5000));
        Items.Add(1);
        Console.WriteLine("HistoryLoaded");
    }
    public void CallForNewData(IAsyncResult result)
    {
       Console.WriteLine("Result: {0}",result.AsyncState);
    }

    public void LoadNewPointsAsync(List<int> Items)
    {
        //while(!History.IsCompleted)
        //{
            System.Threading.Thread.Sleep(100);
        //}
        Action<List<int>> GetPointsInformation = new Action<List<int>>(GetPoints);
        IAsyncResult NewPoints = GetPointsInformation.BeginInvoke(Items, null, null);
    }

    public void GetPoints(List<int> Items)
    {
        Random rnd = new Random();
        System.Threading.Thread.Sleep(rnd.Next(1, 5000));
        Items.Add(2);
        Console.WriteLine("New data loaded");
    }
}
}

编辑:

IAsyncResult History = GetHistoryInformation.BeginInvoke(Items, new AsyncCallback(CallForNewData), Items);

已解决的问题。

Answer 1

来自documentation :

The BeginInvoke method initiates the asynchronous call. It has the same parameters as the method that you want to execute asynchronously, plus two additional optional parameters. The first parameter is an AsyncCallback delegate that references a method to be called when the asynchronous call completes. The second parameter is a user-defined object that passes information into the callback method.

你传递一个null，你得到一个null。