Auto-complete Textbox

Implementing an auto-complete textbox is a rather easy task, as it is all built in to WinForms.

I will be using and referring to a text box here named textBox1.

Auto-complete Mode

This setting will determine whether the auto-complete items will be suggested to your user or appended onto their text (or even both):

Suggest:

Append:

Suggest and Append:

You can set the mode either in the Properties window in the IDE or via code:

textBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;

Auto-complete Source

We will use a custom auto-complete source, so we specify the strings easily:

textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;

You can view MSDN for the other types of sources you can use such as the File System and Recently Used.

Auto-complete Custom Source

I will name the auto-complete collection, AutoCompleteList:

AutoCompleteStringCollection AutoCompleteList = new AutoCompleteStringCollection();

To add items to our list:

AutoCompleteList.Add("http://www.google.com/");
AutoCompleteList.Add("http://www.yahoo.com/");
AutoCompleteList.Add("http://www.bing.com/");

To get more functionality out of our auto-complete box, we are able to load the items from a text file:

foreach (string AutoCompleteItem in System.IO.File.ReadAllLines(Application.StartupPath + "\\AutoList.txt"))
{
AutoCompleteList.Add(AutoCompleteItem);
}

This code will look for a file called AutoList.txt in the same directory you are running your application from, it will then load and add each new item. Of course your items could come from a number of other sources including a database.

We then need to link the source to the text box:

textBox1.AutoCompleteCustomSource = AutoCompleteList;

Complete Code

AutoCompleteStringCollection AutoCompleteList = new AutoCompleteStringCollection();
 
foreach (string AutoCompleteItem in System.IO.File.ReadAllLines(Application.StartupPath + "\\AutoList.txt"))
{
AutoCompleteList.Add(AutoCompleteItem);
}
 
textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
textBox1.AutoCompleteCustomSource = AutoCompleteList;
textBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;

Warnings

• Auto-complete will not work on multi-line text boxes.