AutoComplete TextBox in C#

Most of the developers are familiar with the auto completion text feature available in browsers, search controls and other controls. The auto completion feature is when you start typing some characters in a control, the matching data is loaded automatically for you.

In Visual Studio 2005, some of the controls support this feature including the ComboBox and the TextBox controls. By using these features, we can build Internet Explorer like auto completion functionality in our Windows Forms applications.

Now, we can have a combo box that completes URLs as soon as you type any character. For example, in Figure 1, I typed "c-s" and I see all the URLs starting with "c-s".


Figure 1. Auto Completion in a ComboBox

The AutoCompleteSource and AutoCompleteMode properties of the TextBox and ComboBox controls allow developers to provide automatic completion text feature. You can set both of these properties at design-time as well as at run-time. If you click on AutoCompleteSource drop down, you will see all the options in the drop-down list. See Figure 2.


Figure 2. AutoCompleteSource options

Figure 3 shows AutoCompleteMode options.


Figure 3. AutoCompleteMode options

You can also set these properties at run-time using the following code:  

comboBox1.AutoCompleteSource = AutoCompleteSource.AllSystemSources;
comboBox1.AutoCompleteMode =

The AutoCompleteSource Enumeration has following members:

  • AllSystemResources - Specifies the equivalent of FileSystem and AllUrl as the source. This is the default value when AutoCompleteMode has been set to a value other than the default.
  • AllUrl - Specifies the equivalent of HistoryList and RecentlyUsedList as the source.
  • CustomSource - Specifies strings from a built-in AutoCompleteStringCollection as the source.
  • FileSystem - Specifies the file system as the source. 
  • FileSystemDirectories - Specifies that only directory names and not file names will be automatically completed.
  • HistoryList - Includes the Uniform Resource Locators (URLs) in the history list.
  • ListItems - Specifies that the items of the ComboBox represent the source.
  • None - Specifies that no AutoCompleteSource is currently in use. This is the default value of AutoCompleteSource.
  • RecentlyUsedList - Includes the Uniform Resource Locators (URLs) in the list of those URLs most recently used.

The AutoCompleteMode enumeration has following members:

  • Append - Appends the remainder of the most likely candidate string to the existing characters, highlighting the appended characters.
  • None - Disables the automatic completion feature for the ComboBox and TextBox controls.
  • Suggest - Displays the auxiliary drop-down list associated with the edit control. This drop-down is populated with one or more suggested completion strings.
  • SuggestAppend - Applies both Suggest and Append options.

Loading Custom Source 

We can also specify a custom source from where the listing will be loaded. If you click on the AutoCompleteCustomSource property, it will open the String Collection Editor, where we can add our strings. For example, I add following strings to the strings list. See Figure 4.


Figure 4. Custom Source strings

Now we need to set AutoCompleteSource to CustomSource:

comboBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;

And when I run and type "v" in the combo box, I see VB.NET Heaven. See Figure 5.


Figure 5. Custom Source listing

We can also create AutoCompleteStringCollection programmatically. The following code creates an AutoCompleteStringCollection, adds strings to the collection, and sets it to the AutoCompleteCustomSource of the ComboBox. 

// AutoCompleteStringCollection
AutoCompleteStringCollection data = new AutoCompleteStringCollection();
"Mahesh Chand");
"Mac Jocky");
"Millan Peter");
comboBox1.AutoCompleteCustomSource = data;

Now running the sample and typing "m" in the ComboBox loads the data as shown in Figure 6.


Figure 6. Loading custom data


The AutoComplete feature of ComboBox and TextBox controls allow us to set the auto complete text feature. In this article, we saw how to use this feature in our application at design-time as well as at run-time.

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