Question

我无法找到与我匹配的特定问题，我认为这与我使用一个参数（字符串）创建EventArgs的子类这一事实有关。当我尝试编译时，它似乎告诉我ScanInfoEventArgs没有一个构造函数，当它显然（至少对我来说）。

我只包含了我认为适用的代码。看起来这么简单，我不知所措。

 public partial class MainWindow : Window
{
    Coffee coffeeOnHand;
    SweetTea sweetTeaOnHand;
    BlueberryMuffin blueberryMuffinOnHand;

    public MainWindow()
    {
        InitializeComponent();

        //The following reads the inventory from file, and assigns each inventory item to the Coffee, SweatTea 
        //and BlueberryMuffin objects in memory.
        using (Stream input = File.OpenRead("inventory.dat"))
        {
            BinaryFormatter formatter = new BinaryFormatter();
            coffeeOnHand = (Coffee)formatter.Deserialize(input);
            sweetTeaOnHand = (SweetTea)formatter.Deserialize(input);
            blueberryMuffinOnHand = (BlueberryMuffin)formatter.Deserialize(input);
        }

        //The following adds whatever information is loaded from the objects on file from above
        //into the dropdown box in the menu.
        SelectedItemDropdown.Items.Add(coffeeOnHand);
        SelectedItemDropdown.Items.Add(sweetTeaOnHand);
        SelectedItemDropdown.Items.Add(blueberryMuffinOnHand);
    }

    public class ScanInfoEventArgs : EventArgs
    {
        ScanInfoEventArgs(string scanType)
        {
            this.scanType = scanType;
        }
        public readonly string scanType;
    }

    public class Scan
    {
        //Delegate that subscribers must implement
        public delegate void ScanHandler (object scan, ScanInfoEventArgs scanInfo);

        //The event that will be published
        public event ScanHandler onScan;

        public void Run()
        {
            //The ScanInfoEventArgs object that will be passed to the subscriber.
            ScanInfoEventArgs scanInformation = new ScanInfoEventArgs("scanType");

            // Check to see if anyone is subscribed to this event.
            if (onScan != null)
            {
                onScan(this, scanInformation);
            }
        }
    }

Answer 1

您需要创建构造函数public。所有班级成员都默认为private，这意味着外界无法接触到他们。

由于编译器没有看到匹配的 public 构造函数（因为代码实际上可以调用一个），它会抛出你看到的错误。

正确的代码：

    public ScanInfoEventArgs(string scanType)
    {
        this.scanType = scanType;
    }

请注意，如果所有代码都驻留在同一个程序集中，internal也可以正常工作。

EventArgs不包含带有1个参数的构造函数

1 个答案: