C# 委托 父窗口与子窗口间传值

1）目标

父窗口与子窗口都有1个Button和1个Label。

目标1：单击父窗口的Button，子窗口的Label将显示父窗口传来的值。

目标2：单击子窗口的Button，父窗口的Label将显示子窗口传来的值。

2）父窗口代码

using System;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp5
{
    public delegate void ShowMessageService(string msg);
    public partial class FormMain : Form
    {
        private FormChild childForm = new FormChild();
        public FormMain()
        {
            InitializeComponent();
        }

        private void FormMain_Load(object sender, EventArgs e)
        {
            childForm.showMessageChild = new ShowMessageService(UpdateLabel);
            childForm.Show();
        }

        public async void UpdateLabel(string msg)
        {
            await Task.Delay(2000);
            this.label1.Text = msg;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ShowMessageService sms = new ShowMessageService(childForm.UpdateLabel);
            this.BeginInvoke(sms, "Message from FormMain");
        }

    }
}

3）子窗口代码

using System;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp5
{
    public partial class FormChild : Form
    {
        public ShowMessageService showMessageChild;
        public FormChild()
        {
            InitializeComponent();
        }

        public async void UpdateLabel(string msg)
        {
            await Task.Delay(2000);
            this.label1.Text = msg;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.BeginInvoke(showMessageChild, "Message from FormChild");
        }
    }
}

 4）解释

4.1)定义委托

public delegate void ShowMessageService(string msg);

4.2）父窗口向子窗口传递消息

①由于父窗口拥有子窗口对象，所以直接利用子窗口的方法来创建委托对象，然后用this.BeginInvoke进行异步调用。

        private void button1_Click(object sender, EventArgs e)
        {
            ShowMessageService sms = new ShowMessageService(childForm.UpdateLabel);//定义委托对象，指向子窗口的UpdateLabel方法。
            this.BeginInvoke(sms, "Message from FormMain"); //执行的是子窗口的UpdateLabel方法
        }

4.3）子窗口向父窗口传递消息

①子窗口声明委托对象

    public partial class FormChild : Form
    {

       public ShowMessageService showMessageChild;//声明

    }

②在主窗口给委托对象赋值。

    public partial class FormMain : Form
    {
        private FormChild childForm = new FormChild();
        private void FormMain_Load(object sender, EventArgs e)
        {
            childForm.showMessageChild = new ShowMessageService(UpdateLabel); //子窗口的委托对象指向父窗口的UpdateLabel方法。
            childForm.Show();
        }

    }

③子窗口用this.BeginInvoke进行异步调用。

         private void button1_Click(object sender, EventArgs e)
        {
            this.BeginInvoke(showMessageChild, "Message from FormChild");
        }