C# 事件核心：委托定義、郵件管理器與傳真接收者

編輯：關於C語言

委托與事件定義


public delegate void MailMsgEventHandler(object sender, MailMsgEventArgs e);

public class MailManager
{
    public event MailMsgEventHandler MailMsg; // 事件

    protected virtual void OnMailMsg(MailMsgEventArgs e)
    {
        MailMsg?.Invoke(this, e); // C# 6.0+ null 條件運算子
    }

    public void SimulateArrivingMsg(string from, string to, string subject, string body)
    {
        var e = new MailMsgEventArgs(from, to, subject, body);
        OnMailMsg(e);
    }
}

傳真接收者實作


public class Fax
{
    private readonly TextBox _tBox;
    public Fax(MailManager mm, TextBox tBox)
    {
        _tBox = tBox;
        mm.MailMsg += FaxMsg; // 訂閱
    }
    private void FaxMsg(object sender, MailMsgEventArgs e)
    {
        _tBox.Text += $"消息到傳真：\n來自:{e.from}\n發到:{e.to}\n主題:{e.subject}\n內容:{e.body}\n\n";
    }
    public void Register(MailManager mm) => mm.MailMsg += FaxMsg;
    public void UnRegister(MailManager mm) => mm.MailMsg -= FaxMsg;
}

事件參數類別


public class MailMsgEventArgs : EventArgs
{
    public readonly string from, to, subject, body;
    public MailMsgEventArgs(string from, string to, string subject, string body)
    {
        this.from = from; this.to = to; this.subject = subject; this.body = body;
    }
}