C# 如何防止空委托？

我在stackoverflow和其他网站上搜索了两天，试图找出为什么我得到一个空委托。我讨厌发布一个已经回答过的问题，但我对这个问题迷茫了。请原谅我，如果这已经在这个网站上的某个地方

我的目标是将一些值从一种形式传递到另一种形式。但是delPassData总是空的

我的主窗体是Form1，我试图从另一个窗体formNewThread向它发送值。以下是formNewThread中的相关代码：

public partial class formNewThread : Form
{
    public delegate void delPassDataEventHandler(string where, string newThd); //declare delegate to communicate with Form1
    public event delPassDataEventHandler delPassData;

    private string newThread;
    private string whereUsed;

    public formNewThread(string whereTo, ComboBox cb)
    {
        InitializeComponent();

        whereUsed = whereTo;

        ... removed some code here

    }

    public formNewThread()
    {
        InitializeComponent();
    }

    private void buttonPublish_Click(object sender, EventArgs e)
    {
        newThread = textNewThread.Text;

        ... removed code here

                if (delPassData != null)
                    delPassData(whereUsed, newThread);

                this.Close();

    }

表1中的相关代码为：

    public Form1()
    {
        try
        {
            InitializeComponent();

            frmNewThd.delPassData += new formNewThread.delPassDataEventHandler(frmNewThd_delPassData);
            newCsg.delPassData += new NewCsg.delPassDataEventHandler(newCsg_delPassData);

          ... removed code

    }

    void frmNewThd_delPassData(string where, string newThd) //this routine communicates with with delegate in form formNewThread
    {
        if (where == "Lnr1")
        {
            comboLinerThread.Text = newThd;
        }
        else if (where == "Body")
        {
            comboBodyThdDown.Text = newThd;
        }
        else if (where == "SetTool")
        {
            comboSetToolThd.Text = newThd;
        }
    }

下面是我测试的简单模型，用于实现您在上面第一个程序中看到的代理

  using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Data;
  using System.Drawing;
  using System.Linq;
  using System.Text;
  using System.Windows.Forms;

  namespace SendDataWithDelegate
  {
  public partial class Form1 : Form
  {
    private Form2 frm2 = new Form2();
    private Form3 frm3 = new Form3();

    public Form1()
    {
        InitializeComponent();

        frm2.delPassData += new Form2.delPassDataEventHandler(frm2_delPassData); //declaring a new event handler for Form2
        frm3.delPassData += new Form3.delPassDataEventHandler(frm3_delPassData); //declaring a new event handler for Form3
    }

    void frm3_delPassData(double od, double id, double length, double yield) //this routine communicates with delegate in Form3
    {
        labelOD.Text = String.Format("{0:F3}", od);
        labelID.Text = String.Format("{0:F3}", id);
        labelLength.Text = String.Format("{0:F3}", length);
        labelYield.Text = String.Format("{0:N0}", yield);
    }

    void frm2_delPassData(string city, string state) //this routine communicates with delegate in Form2
    {
        labelCity.Text = city;
        labelState.Text = state;
    }

    private void buttonOpenForm2_Click(object sender, EventArgs e) //launch Form2
    {
        frm2.Show();
    }

    private void buttonOpenForm3_Click(object sender, EventArgs e) //launch Form3
    {
        frm3.Show();
    }
}

}

}

---

}

您可以将事件初始化为公共事件delPassDataEventHandler delPassData=委托{}@MukeshRawat这是一个相当苛刻的解决方案。如果没有要引发的事件，为什么要引发它并降低应用程序的速度？@OndrejJanacek调用没有主体的方法是一个非常快的操作。事实上，按照检查空值的顺序。@Servy好的，但我仍然觉得这是一个相当愚蠢的解决方案。鲍勃，你能举一个简单的例子来说明这个问题吗。事实上，您有很多代码实际上与复制问题无关，如果您能够删除复制问题所不需要的代码，那么对它们进行排序就会容易得多。

  using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Data;
  using System.Drawing;
  using System.Linq;
  using System.Text;
  using System.Windows.Forms;

  namespace SendDataWithDelegate
  {
      public partial class Form2 : Form
      {
          public delegate void delPassDataEventHandler(string city, string state); //declare a delegate to communicate with Form1
          public event delPassDataEventHandler delPassData; //declare an event name for the delegate's event handler

    public Form2()
    {
        InitializeComponent();
    }

    private void buttonSendData_Click(object sender, EventArgs e)
    {
        if (delPassData != null)
            delPassData(textCity.Text, textState.Text); //executes if the "delPassData event" occurrs 
    }
}

  using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Data;
  using System.Drawing;
  using System.Linq;
  using System.Text;
  using System.Windows.Forms;

  namespace SendDataWithDelegate
  {
  public partial class Form3 : Form
  {
    public delegate void delPassDataEventHandler(double od, double id, double length, double yield); //declare a delegate to communicate with Form1
    public event delPassDataEventHandler delPassData; //declare an event name for the delegate's event handler

    double ODia;
    double IDia;
    double Len;
    double Sy;

    public Form3()
    {
        InitializeComponent();
    }

    private void buttonSendData_Click(object sender, EventArgs e)
    {
        ODia = Convert.ToDouble(textOD.Text);
        IDia = Convert.ToDouble(textID.Text);
        Len = Convert.ToDouble(textLength.Text);
        Sy = Convert.ToDouble(textYield.Text);

        if (delPassData != null)
            delPassData(ODia, IDia, Len, Sy); //executes if the "delPassData event" occurrs 
    }
}