C＃：ListView不会添加来自另一个类的项目

Question

Good day,

I'm new to whole programming thing and can't figure out / find a solution. I've been trying to populate my ListView with Items that come from another Class. But the ListView doesn't seem to do anything when the Class2 returns an Array .

Here is how i make it :

1 ) I search for something and send the value to Class2 ( Main Class in Form1 ):

private void tbSearch_KeyDown(object sender, KeyEventArgs e)
    {
        Class2 cl2 = new Class2();

        if (e.KeyCode == Keys.Enter)
        {
            if (string.IsNullOrEmpty(tbSearch.Text))
            {
                MessageBox.Show("The Textbox is Empty.....");
            }
            else
            {
               listV.Items.Clear(); 
               cl2.Search(tbSearch.Text);  // Give a value to Method in Class2
            }
        }
    }

2 ) Then in Class2 i do some internet search and return arrays with the Results :

public async void Search(string search_value)
    {
            /*** Read the XML Data that i've got from Response ****/

            foreach (XmlNode node in XMLlist)
            {
                /****** Get the values that i need and write them into an array *******/

                string[] result = new string[10];

                result[0] = series_title;
                result[1] = series_type;
                result[2] = series_episodes;
                result[3] = series_score;
                result[4] = series_id;
                result[5] = series_title_english;
                result[6] = series_status;
                result[7] = series_start_date;
                result[8] = series_end_date;
                result[9] = series_image;

                Form1 fm1 = new Form1();
                fm1.Update_SearchList(result); // Return an array to Form1
            }
    }

3) And at the end i try to populate the ListView with the returned array ( Form1 again ) :

public void Update_SearchList(string [] array)
    {
        ListViewItem item = new ListViewItem(array);
        this.listV.BeginUpdate();                
        this.listV.Items.Add(item); // Here the Item.Add() Method doesn't add new Items to the ListView or they just aren't being shown.
        this.listV.EndUpdate();          
    }

The listView.View is set to Details and the columns are being generated on Form.Load .

Is there a problem with how i execute the listView.Items.Add(); Method or is there another problem ?

When i try to do this whole operation in one single private void tbSearch_KeyDown(object sender, KeyEventArgs e) everythings works.

Thank you for your time and have a good day !

Answer 1

You created a new instance of Form1 in Form1 fm1 = new Form1(); , which is not the instance of your caller.

I would suggest you return the result from Search() and process in Form1 , or better, a callback function.

I haven't tried but a quick bypass solution could passing Form1 as a reference to the Search() function, but TBH it looks nasty to me.

private void tbSearch_KeyDown(object sender, KeyEventArgs e) {
    //...
           cl2.Search(tbSearch.Text, ref this); // pass the ref of current instance to cl2
        }
    }
}

public async void Search(string search_value, ref Form1 frm) {
    //...
    foreach (XmlNode node in XMLlist) {
        // ...
        frm.Update_SearchList(result); // use the frm reference instead
    }
}

public void Update_SearchList(string [] array) {
    if (InvokeRequired)
        BeginInvoke(new MethodInvoker(() => Update_SearchList(array)));
    else {
        ListViewItem item = new ListViewItem(array);
        this.listV.BeginUpdate();                
        this.listV.Items.Add(item);
        this.listV.EndUpdate();  
    }        
}

Note: code not tested, just a quick idea!!!

Also, I don't think if your async will work as expected if called in a non-async function.

Edit:

You can also try to return results and proceed in main form. Find the draft code as follows, but it's synced and may block your UI thread. Again, code untested !

private void tbSearch_KeyDown(object sender, KeyEventArgs e) {
    //...
            var results = cl2.Search(tbSearch.Text);
            foreach (var item in results) Update_SearchList(item);
        }
    }
}

public List<xxx> Search(string search_value) {
    //...
    var results = new List<xxx>(); // change type to the correct type
    foreach (XmlNode node in XMLlist) {
        // ...
        results.Add(result);
    }
    return results;
}