C＃-event handler - 将值从一种形式传递到另一种形式 [英] C# -event handler -passing value from one form to another

问题描述

嗨！

我创建了委托和事件，并尝试在form1上订阅事件，但如果我将事件订阅代码移动到form2那么它就会获得subscibe，那么就没有问题了。可以任何人找我plz。在此先感谢::::

Hi!
I have created delegate and event and try to subscribe event on form1 but it dot get subscibe if i will move event subscribe code to form2 then there is not problem. can any one have look for me plz. thanks in advance::::

_mainform(form1):

        namespace KasseDelegate
{

    public delegate void ListViewUpdatedEventHandler(object sender, ListViewUpdatedEventArgs e);
    public partial class Form1 : Form
    {
        private Form3 frm3;

        public Form1()
        {
            InitializeComponent();
            frm3 = new Form3();
            frm3.ListViewUpdated += new ListViewUpdatedEventHandler(Frm3_ListViewUpdated1);

        }

        private void Frm3_ListViewUpdated1(object sender, ListViewUpdatedEventArgs e)
        {
            MessageBox.Show("hi");
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form2 frm2 = new Form2();
            frm2.Show();

        }

    }
}

_searchform（form2）：

_searchform(form2) :

public partial class Form2 : Form
       {

           public Form2()
           {
               InitializeComponent();
           }

           private void button1_Click(object sender, EventArgs e)
           {
               using (SQLiteConnection con = new SQLiteConnection(Properties.Settings.Default.ConnectionString))
               {
                   con.Open();
                   SQLiteCommand cmd = new SQLiteCommand("select * from varer where varenummer=@Varenummer", con);
                   cmd.Parameters.AddWithValue("@Varenummer", "101");

                   SQLiteDataReader dr = cmd.ExecuteReader();
                   Form3 frm3 = new Form3(dr);
                   frm3.Show();
               }
           }
       }

表格3：

Form 3 :

namespace KasseDelegate
{

    public partial class Form3 : Form
    {
        public event ListViewUpdatedEventHandler ListViewUpdated;
        SQLiteDataReader dr1;
        public Form3()
        {
            InitializeComponent();

        }
        public Form3(SQLiteDataReader dr)
        {
            InitializeComponent();
            dr1 = dr;
        }

        private void Form3_Load(object sender, System.EventArgs e)
        {
            if (dr1 != null)
            {

                while (dr1.Read() == true)
                {
                    ListViewItem LVI = new ListViewItem();
                    LVI.SubItems.Add(dr1[0].ToString());
                    LVI.SubItems.Add(dr1[1].ToString());
                    LVI.SubItems.Add(dr1[2].ToString());
                    LVI.SubItems.Add(dr1[3].ToString());
                    LVI.SubItems.Add(dr1[4].ToString());
                    listView1.Items.Add(LVI);

                }
            }

我的尝试：



我已经提交了代码，我已尽力找出问题，因为nd无法理解。 plz plz帮帮我

What I have tried:

I have submitted the code and i have tried my best to find out what is problem in that nd not able to understand. plz plz help me out

推荐答案

嗯......这很简单易懂。

你在Form1中创建一个Form3实例附上一个处理程序：

Well...that's pretty simple to understand.
You create an instance of Form3 in Form1 and you attach a handler:

frm3 = new Form3();
frm3.ListViewUpdated += new ListViewUpdatedEventHandler(Frm3_ListViewUpdated1);

但是你从不显示表单，所以实际的Listview永远不会更新。

相反，在Form2中你创建一个Form3的实例并显示它，但是你从不附加处理程序：

But you never show teh form, so the actual Listview never gets updated.
Conversely, in Form2 you create an instance of Form3 and show it, but you never attach a handler:

Form3 frm3 = new Form3(dr);
frm3.Show();

因此，该版本更新了ListView，并且（可能是你没有表明这样做）发出信号，但你还没有一个处理程序，所以没有任何反应。



看看这个：在两种形式之间传递信息，第2部分：儿童到父母 [ ^ ]

示例代码应该显示您要做什么。

So that version gets it's ListView updated, and (presumably, you don't show it doing that) signals the event, but you don't have a handler so nothing happens.

Have a look at this: Transferring information between two forms, Part 2: Child to Parent[^]
The sample code should show you what to do.

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