System.ArgumentNullException

Question

我收到這個例外...

System.ArgumentNullException: Value cannot be null.
Parameter name: typeName
   at HomeInventory2.Services.Factory.GetService(String servicename) in C:\Users\Protego\Documents\Visual Studio 2010\Projects\HomeInventory2\HomeInventory2\Services\Factory.cs:line 37
   at HomeInventory2.Business.Manager.GetService(String name) in C:\Users\Protego\Documents\Visual Studio 2010\Projects\HomeInventory2\HomeInventory2\Business\Manager.cs:line 14
   at HomeInventory2.Business.InventoryMngr.Create(CreateInventory inv) in C:\Users\Protego\Documents\Visual Studio 2010\Projects\HomeInventory2\HomeInventory2\Business\InventoryMngr.cs:line 19
   at HomeInventory2.Form1.submitButton_Click(Object sender, EventArgs e) in C:\Users\Protego\documents\visual studio 2010\Projects\HomeInventory2\HomeInventory2\Form1.cs:line 52
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

從此代碼中摘取-

private void submitButton_Click(object sender, EventArgs e)
        {
            CreateInventory create = new CreateInventory();
            create.ItemAmount = textBoxAmount.Text;
            create.ItemCategory = textBoxCategories.Text;
            create.ItemProperties = textBoxValue.Text;
            create.ItemValue = textBoxValue.Text;

            InventoryMngr invtryMngr = new InventoryMngr();
            invtryMngr.Create(create);

        }

該代碼應以創建的文件結尾，並將這些值保存到文本文件中。 顯然，這方面發生了一些變化-我假設在InventoryMngr文件中看起來像這樣。

namespace HomeInventory2.Business
{
    public class InventoryMngr : Manager
    {
        /// <summary>
        /// persists the inventory information
        /// </summary>
        /// <param name="inv"></param>
        public void Create(CreateInventory inv)
        {
            InventorySvc inventorySvc =
            (InventorySvc)GetService(typeof(InventorySvc).Name);
            inventorySvc.CreateInventory(inv);
        }
    }
}

業務經理獲得服務

namespace HomeInventory2.Business
{
    public abstract class Manager
    {
        private Factory factory = Factory.GetInstance();
        protected IService GetService(String name)
        {
            return factory.GetService(name);
        }
    }
}

和工廠getservice

public IService GetService(string servicename)
{
    Type type;
    Object obj = null;
    try
    {
        type = Type.GetType(GetImplName(servicename));
        obj = Activator.CreateInstance(type);
    }
    catch (Exception e)
    {
        Console.WriteLine("Exception occured: {0}", e);
        throw e;
    }
    return (IService)obj;
}

GetImplName

private string GetImplName(string servicename)
        {
            NameValueCollection settings =
                ConfigurationManager.AppSettings;
            return settings.Get(servicename);
        }

Answer 1

這是您的問題：

NameValueCollection settings = ConfigurationManager.AppSettings;
return settings.Get(servicename);

確保您的app.config / web.config具有正確的AppSettings值。 settings.Get(servicename)沒有找到一鍵servicename 。

因此，如果服務名稱為“ AwesomeService”，則需要在appSettings中添加一個元素，例如：

<add key="AwesomeService" value="somevalue"/>

Answer 2

我像下面這樣修改您的代碼：

public void Create(CreateInventory inv)
{
    InventorySvc inventorySvc =
        (InventorySvc)GetService((typeof(InventorySvc)).toString());
    inventorySvc.CreateInventory(inv);
}