C＃将ListView项目从函数传递到表单上的ListView？

Question

i am trying to do the following:

I have a function.. which Queries SQL and gets some data from a database.. now i want to display those values in a listview which is on a form. The function is in a SQL Class.

It works for one item only, but if i want for example 5 items to be passed it wont work since it only passes the last time, which is logical when you see the code.

I cant seem to figure out, how to "referance" a listvie object from a form to the function and pass the items to it.

Here is the code: (i know it returns only one item now, i tried different things.. none worked):

    public ListViewItem SQL_GetLogsHistory(string WKS)
    {
        SqlCommand mySQLCommand = new SqlCommand(Properties.Settings.Default.SQL_GetLogsHistroy, SQLconn);
        mySQLCommand.Parameters.AddWithValue("@WKS", WKS);
        SqlDataReader reader = mySQLCommand.ExecuteReader();
        ListViewItem item = new ListViewItem();


        while (reader.Read())
        {
            item = new ListViewItem(new[] { 

                reader.GetValue(4).ToString(), // Timestamp
                reader.GetValue(2).ToString() // Log

            });

        }

        reader.Close();
        return item;
    }

Answer 1

you can have list of items

List<ListViewItem> items = new List<ListViewItem>();

inside your loop create new ListViewItem and set the properties and add it to list

    while (reader.Read())
    {
        ListViewItem item = new ListViewItem();
        item = new ListViewItem(new[] { 

            reader.GetValue(4).ToString(), // Timestamp
            reader.GetValue(2).ToString() // Log

        });
      items.Add(item);

    }

finally return items from the method and change the signature of the method as below

public List<ListViewItem> SQL_GetLogsHistory(string WKS)

Side Note: better to use using statements for SqlCommand and SqlDataReader

public List<ListViewItem> SQL_GetLogsHistory(string WKS)
{
    List<ListViewItem> items = new List<ListViewItem>();
    using (SqlCommand mySQLCommand = new SqlCommand(Properties.Settings.Default.SQL_GetLogsHistroy, SQLconn))
    {
        mySQLCommand.Parameters.AddWithValue("@WKS", WKS);
        using (SqlDataReader reader = mySQLCommand.ExecuteReader())
        {
            while (reader.Read())
            {
                ListViewItem item =  new ListViewItem(new[] { 
                            reader.GetValue(4).ToString(), // Timestamp
                            reader.GetValue(2).ToString() // Log
                        });
                items.Add(item);
            }
        }

    }
    return items;
}

Answer 2

You could use yield return:

   public IEnumerable<ListViewItem> SQL_GetLogsHistory(string WKS)
    {
        SqlCommand mySQLCommand = new SqlCommand(Properties.Settings.Default.SQL_GetLogsHistroy, SQLconn);
        mySQLCommand.Parameters.AddWithValue("@WKS", WKS);
        SqlDataReader reader = mySQLCommand.ExecuteReader();
        ListViewItem item = new ListViewItem();


        while (reader.Read())
        {
            yield return new ListViewItem(new[] { 

                reader.GetValue(4).ToString(), // Timestamp
                reader.GetValue(2).ToString() // Log

            });

        }

        reader.Close();
        return item;
    }

This will reduce multiple enumeration of your data. You can then use this method to create a List<ListViewItem> if required:

var list = SQL_GetLogsHistory(WKS).ToList();

Or you could directly use this as your list view data source:

listView.DataSource = SQL_GetLogsHistory(WKS);

Answer 3

Do you just need to return a List<ListViewItem> like this?

public List<ListViewItem> SQL_GetLogsHistory(string WKS)
{
    SqlCommand mySQLCommand = new SqlCommand(Properties.Settings.Default.SQL_GetLogsHistroy, SQLconn);
    mySQLCommand.Parameters.AddWithValue("@WKS", WKS);
    SqlDataReader reader = mySQLCommand.ExecuteReader();
    List<ListViewItem> items = new List<ListViewItem>();

    while (reader.Read())
    {
        var item = new ListViewItem(new[] { 

            reader.GetValue(4).ToString(), // Timestamp
            reader.GetValue(2).ToString() // Log

        });

        items.Add(item);
    }

    reader.Close();
    return items;
}