Make a Searchable ComboBox with .NET

with C# or VB.NET

by William Ryan

Have you wanted to make a searchable ComboBox in .NET?  Well, it's pretty easy.  There are many ways to implement this, but in a nutshell, all you need to do is trap the KeyPress event, use the KeyPress' Keychar and then call the ComboBox's FindString method.  If you don't find the search text, you'll return a -1 as an index, if you do find the text, then the index will be the index the item exists in the list.  So, if we find the text, we don't want to allow the keypress, otherwise we'd have 2 first letters in the combobox.  However if you don't want to find it, you wan't to let them type in a value.  Here's all there is to it:

VB.NET

Private Sub CombBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles ComboBox1.KeyPress         Dim findString As String = String.Empty         If (Not e.KeyChar.IsLetterOrDigit(e.KeyChar, 0)) Then Exit Sub         findString = e.KeyChar         With ComboBox1             .SelectedIndex = ComboBox1.FindString(findString)         End With         If ComboBox1.SelectedIndex > -1 Then e.Handled = True End Sub

C#

private void comboBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e) {    string findString = string.Empty;     comboBox1.SelectedIndex = comboBox1.FindString(e.KeyChar.ToString());    if(comboBox1.SelectedIndex > -1){e.Handled = true;} }