Passing parameters to a method

Question

Is there any way to get a method to recognise different List controls, At present I'm having to write three almost identical methods to transfer a list of items from a list box to : -

a) a combobox,

b) another listbox

c) a checkedlistbox

        private void ListToComboCopy(ref ListBox LBx, ref ComboBox CBx)
        {
            int T;
            T = LBx.Items.Count;
            CBx.Items.Clear();
            for (int i = 0; i < T; i++)
            {
                CBx.Items.Add(LBx.Items[i]);
            }
        }

        private void ListToCheckListCopy(ref ListBox LBx, ref CheckedListBox CBx)
        {
            int T;
            T = LBx.Items.Count;
            CBx.Items.Clear();
            for (int i = 0; i < T; i++)
            {
                CBx.Items.Add(LBx.Items[i]);
            }
        }

        private void ListToListCopy(ref ListBox LBx, ref ListBox CBx)
        {
            int T;
            T = LBx.Items.Count;
            CBx.Items.Clear();
            for (int i = 0; i < T; i++)
            {
                CBx.Items.Add(LBx.Items[i]);
            }
        }

I'm sure there must be a way to use just one method for all three! (I can do it in Visual Basic, but can't seem to find out how in C#.)

Answer 1

Hi,

method overloading is a common way and is the way to go, if you dont want to check for the types inside your method. So either use it your way, or pass a base-object like System.Windows.Forms.Control as parameter and check inside the method for the type.

        private void Form1_Load(object sender, EventArgs e)
        {
            GetSomeMsg(this);
        }

        private void GetSomeMsg(Control ctrl)
        {
            if (ctrl is Form)
                MessageBox.Show("yes");
            else if (ctrl is ComboBox)
                MessageBox.Show("no");
        }

Regards,

  Thorsten

Answer 2

The Items property of a ListBox, ComboBox and CheckedListBox are all of type ObjectCollection. Better still, this implements IList.

So you could just have a single method that takes an IList, and call it by passing in the Combobox.Items property or ListBox.Items property etc.

private void ListToListCopy(ListBox LBx, IList list)
{
            int T;
            T = list.Count;
            list.Clear();
            for (int i = 0; i < T; i++)
            {
                list.Add(LBx.Items[i]);
            }
}

// ... elsewhere in your code ...

ListToListCopy(SourceListBox, DestListBox.Items);

ListToListCopy(SourceListBox, DestComboBox.Items);

// ... etc

P.S. Note I do not pass the arguments by ref. This is unnecessary since you are not changing the actual controls passed in (only the items contained in their Items property).

Answer 3

The Items property of a ListBox, ComboBox and CheckedListBox are all of type ObjectCollection. Better still, this implements IList.

So you could just have a single method that takes an IList, and call it by passing in the Combobox.Items property or ListBox.Items property etc.

private void ListToListCopy(ListBox LBx, IList list)
{
            int T;
            T = list.Count;
            list.Clear();
            for (int i = 0; i < T; i++)
            {
                list.Add(LBx.Items[i]);
            }
}

// ... elsewhere in your code ...

ListToListCopy(SourceListBox, DestListBox.Items);

ListToListCopy(SourceListBox, DestComboBox.Items);

// ... etc

P.S. Note I do not pass the arguments by ref. This is unnecessary since you are not changing the actual controls passed in (only the items contained in their Items property).

Hi,

this is a very good way to solve the problem! Thanks.

Regards,

  Thorsten

Answer 4

Many Thanks!

Worked as soon as I realized that I needed a

"using System.Collections;"

statement as well.

---

Max Symons