Question

using System;

namespace _1._75_Using_a_delegate
{
    public class Program
    {

        public delegate int Calculate(int x, int y);

        public int Add(int x, int y) { return x + y; }
        public int Multiply(int x, int y) { return x * y; }

         public void UseDelegate()
        {


            Calculate calc = Add;
            Console.WriteLine(calc(3, 4)); //Displays 7


            calc = Multiply;
            Console.WriteLine(calc(3, 4));//Displays 12

        }

       public static void Main()
         {

            //call and execute UseDelegate()

         }



    }
}

这应该输出7和12的上述结果。

委托函数不能直接从当前状态的main调用。

为什么不能从主要人员那里看到代表呢？
是否有必要创建一个类？
如何调用委托函数？

Answer 1

您无法从静态方法调用非静态方法，因此您必须实现另一个类，如

Try
        Dim conn As New SqlConnection("Data Source=HAMSE_PC\SQLEXPRESS;Initial Catalog=Body;Integrated Security=True")
        cmd.Connection = conn
        conn.Open()

        Dim UpdateSQL, name, dis, username, pass As String
        name = txtname.Text
        dis = txtdiscription.Text
        username = txtusername.Text
        pass = txtpassword.Text

        UpdateSQL = "Update Users Set "
        UpdateSQL &= "FullName=@fullname,Phone=@phone,Date=@date,Discription=@dis,UserName=@user,Password=@pass "
        UpdateSQL &= "Where User_ID=@ID"



        cmd.CommandText = UpdateSQL

        cmd.Parameters.AddWithValue("@fullname", name)
        cmd.Parameters.AddWithValue("@date", Convert.ToDateTime(txtdate.Text).Date)
        cmd.Parameters.AddWithValue("@dis", dis)
        cmd.Parameters.AddWithValue("@user", username)
        cmd.Parameters.AddWithValue("@pass", pass)
        cmd.Parameters.AddWithValue("@phone", Convert.ToInt32(txtphone.Text).ToString)
        cmd.Parameters.AddWithValue("@ID", Convert.ToInt32(txtid.Text).ToString)

        If txtname.Text = "" Or txtdate.Text = "" Or txtusername.Text = "" Or txtpassword.Text = "" Or txtphone.Text = "" Then
            MessageBox.Show("to update please fill the empty Columns ", "Attention")
            txtname.Focus()
        Else
            cmd.ExecuteNonQuery()

            MsgBox("Updated")
            Dim dt As New DataTable
            Dim ds As New DataSet
            ds.Tables.Add(dt)

            Dim da As New SqlDataAdapter
            da = New SqlDataAdapter("select * from Users", conn)
            da.Fill(dt)

            UsersDataGridView.DataSource = dt.DefaultView
            txtname.Text = ""
            txtdate.Text = ""
            txtusername.Text = ""
            txtpassword.Text = ""
            txtphone.Text = ""

            ID()
        End If
        conn.Close()

    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try

您可以通过主要方法调用它，例如

internal class Check
{
    public delegate int Calculate(int x, int y);

    public int Add(int x, int y)
    {
        return x + y;
    }

    public int Multiply(int x, int y)
    {
        return x * y;
    }

    public void UseDelegate()
    {
        Calculate calc = Add;
        Console.WriteLine(calc(3, 4)); //Displays 7

        calc = Multiply;
        Console.WriteLine(calc(3, 4));//Displays 12
    }
}

Answer 2

你根本没有调用这个方法，现在你不能，因为Main方法是静态的，你的方法不是。

我建议将代码拆分为第二类，这样更容易调用。（而不是使所有方法都是静态的）

public class Assignment
{ /* all code except the Main method goes here */ }

然后，在Main方法中，实例化Assignment类的实例并调用UseDelegate：

public static void Main()
{
    Assignment a = new Assignment();
    a.UseDelegate();

    Console.ReadKey(); // to prevent the console from closing immediate
}

呼叫代理无法访问？

2 个答案: