Less complicated alternative for ListBox.FindString Method (String)

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Hi all,

I have a listBox items string collection like:

Virtual Serial Port (COM1->COM2) COM1
Virtual Serial Port (COM2->COM1) COM2
USB-Serial device COM3

I want to select an item index using: a string like COM1.

I can not use:

C#

int index = listBox1.FindString(Com1);

because Com1 can appear more than one item.

I have a solution, but I want to make it more simple.
This is what I used:

C#

private void loadSettings()
      {
          if(!string.IsNullOrEmpty(settings.LastPort))
          {
              FindMyString( settings.LastPort);
             if(listBox1.SelectedIndex > -1) buttonOpenPort.PerformClick();
          }
      }

      private void FindMyString(string searchString)
      {
          // Ensure we have a proper string to search for.
          if (searchString != string.Empty)
          {
              List<string> ListBox1Coll = new List<string>();
              foreach (string S in listBox1.Items)
              {
                  string resultremove;
                  string result;
                  if (S.Length > 5) resultremove = S.Remove(0, S.Length - 5);
                  else if (S.Length > 4) resultremove = S.Remove(0, S.Length - 4);
                  else if (S.Length > 3) resultremove = S.Remove(0, S.Length - 3);
                  else resultremove = S;
                  result = resultremove.Substring(resultremove.IndexOf('C'));
                  ListBox1Coll.Add(result.Trim(new char[] { '"' }));
              }

              int index;
              for (int i = 0; i < ListBox1Coll.Count; i++)
              {
                  if (ListBox1Coll[i] == searchString)
                  {
                      index = i;
                      if (index != -1)
                          listBox1.SetSelected(index, true);
                      break;
                  }
              }
          }
      }

Posted 26-Apr-14 5:20am

GrooverFromHolland

Updated 26-Apr-14 7:44am

v3

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Comments

[no name] 26-Apr-14 14:22pm

If your strings are all in that same format, why can't you simply take the last character of the string? A '1' would tell you it's COM1, a '2' COM2, etc. Or if that doesn't work for you, get the LastIndex of the space character and SubString the rest of the string to the end giving you the COMx string.

GrooverFromHolland 26-Apr-14 16:02pm

Hi Wes,
You gave me the idea, the last characters of my string are always numbers with a maximum of 255.
I can filter on that.

2 solutions

Solution 1

As long as your ListBox Items have some sub-string that's unique, you can make finding their indexes easy:

C#

private int getListItemIndex(string match)
{
    int ndx = -1;

    foreach (string s in listBox1.Items)
    {
        if (s.Contains(match))
        {
            ndx = listBox1.Items.IndexOf(s);
            break;
        }
    }

    return ndx;
}

Here each of your Items has the unique string space+COM+integer:

C#

private void sampleTest()
{
    int ndx = getListItemIndex(" COM1");

    switch (ndx)
    {
        case -1:
            // handle no match
            break;
        case 0:
            // handle Item 0
            break;
        case 1:
            // handle Item 1
            break;
        case 2:
            // handle Item 2
            break;
    }
}

Obviously, this type of solution depends on an identifiable regular pattern.

Posted 26-Apr-14 8:38am

BillWoodruff

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Alan N · Accepted Answer · 2014-04-26T10:55:00

The listbox item collection can be any type of object, including String, and by default will display the result of obj.ToString();

Now the clever thing is that if a collection is bound via the listbox's DataSource property then the listbox display and the listbox value can be different. The display is governed by the DisplayMember property and the value (returned by SelectedValue) by the ValueMember property.

1) Define a simple class containing two string properties, one for display and one for value.

C#

public sealed class ListBoxItem {
  private String displayField;
  private String valueField;

  public ListBoxItem(String displayString, String valueString) {
    DisplayString = displayString;
    ValueString = valueString;
  }

  public String DisplayString {
    get { return displayField; }
    set { displayField = value; }
  }


  public String ValueString {
    get { return valueField; }
    set { valueField = value; }
  }
}

2) Setup the listbox with a collection of ListBoxItem objects as the DataSource

private void SetupListBox() {
  List<ListBoxItem> myItems = new List<ListBoxItem>();
  myItems.Add(new ListBoxItem("qwerty COMX..COMY", "COM2"));
  myItems.Add(new ListBoxItem("Unreliable COM adapter", "COM5"));
  myItems.Add(new ListBoxItem("Onboard COM", "COM1"));
  // Select DisplayMember and ValueMember with property names from the ListBoxItem class
  lbx.DisplayMember = "DisplayString";
  lbx.ValueMember = "ValueString";
  lbx.DataSource = myItems;
  lbx.SelectedValueChanged += new EventHandler(SelectedValueChanged);
  LoadSettings();
}

private void LoadSettings() {
   // Selecting the item with Value "COM1" will highlight "Onboard COM"
   // and fire SelectedValueChanged
  lbx.SelectedValue = "COM1";
}

private void SelectedValueChanged(object sender, EventArgs e) {
// SelectedValues are ListBoxItem.ValueString
  if (lbx.SelectedValue != null) {
    Debug.Print("Selected port is {0}", lbx.SelectedValue);
  } else {
    Debug.Print("Null - nothing selected");
  }
}

It's a bit of work to setup but gives complete separation of display and value. If SelectedValue is assigned a value which is not in the collection then the highlight is removed and SelectedValue will return null.

Alan.