c#事件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace WindowsFormsApplication1
{

    public class args : EventArgs
    {
        private string str;

        public string Str
        {
            get { return str; }
            set { str = value; }
        }
        public args(string s)
        {
            str = s;
        }


    }
}

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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private string s;

        public string S
        {
            get { return s; }
            set { s = value; }
        }
        public Form1()
        {
            InitializeComponent();
        }
        public delegate string test(args e);
         public event test tt;
        private void Form1_Load(object sender, EventArgs e)
        {
                     if (null != this.tt) 
 
            {
                label1.Text = this.tt.ToString(); ;
            }
           
        }
        }
}

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 WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }


        private void Form2_Load(object sender, EventArgs e)
        {

        }
        public void ShowMessage(object sender, EventArgs e)
        {
            MessageBox.Show("another form call this method!");
        }
        public string print(args e)
        {

            return e.ToString();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            Form1 f = new Form1();
            f.S = "ssss";
                    string str = "null";
            args c = new args(str);
            f.tt += print(c); 
 
            f.ShowDialog();
        }
    }
}

红色代码报错。我想知道 带返回值的事件该如何使用。 c# delegate
[解决办法]
delegate void printhand(evtarg e);
---〉
delegate string printhand(evtarg e);
[解决办法]
事件后面一般是直接跟 函数或者 委托的。

f.tt += print

或者

f.tt += new f.test(print);

[解决办法]
兄弟不是这么用啊，
应该是f.tt += print;

[解决办法]
按照MS推荐的做法，事件通常封装为EventHandler<T> T : EventArgs
也就是事件返回值通常封装在事件参数e中,比如，用你的args.Str作为返回值，可以这么写

public event EventHandler<args> TestEvent;
public void OnTestEvent(args e)
{
    if(this.TestEvent != null)
    {
         return label1.Text = this.TestEvent(e);   //这里获取返回值
    }    
}

Form2
args c = new args(str);
f.TestEvent += print;
f.OnTestEvent(c);  //触发事件

[解决办法]

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 WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent(); 
 
        }
 
        private void Form2_Load(object sender, EventArgs e)
        {
 
        }
        public void ShowMessage(object sender, EventArgs e)
        {
            MessageBox.Show("another form call this method!");
        }
        public args print(args e)
        {
 
            return e; // 返回参数
        }
   
 
        private void button1_Click_1(object sender, EventArgs e)
        {
            Form1 f = new Form1();
            string str = "null";
            args c = new args(str);
            f.tt += print; 
            f.Form1Show(c); //传c
        }
    }
}
 
 
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 WindowsFormsApplication1
{
 
    
 
 
    public partial class Form1 : Form
    {
        public string s { get; set; }
       
        public Form1()
        {
            InitializeComponent();
        }
        public delegate args test(args e);  //返回类型 
 
        public event test tt;
 
        private void Form1_Load(object sender, EventArgs e)
        {
           
        }
 
        public void Form1Show(args e)
        {
 
            if (null != tt)
            {
                label1.Text = tt(e).Str.ToString();
                this.Show();
            }
           
        }
 
    }
 
 
    public class args : EventArgs
    {
        private string str;
 
        public string Str
        {
            get { return str; }
            set { str = value; }
        }
        public args(string s)
        {
            this.str = s;
        }
    }
}