WPF TextBox With Ellipsis

• Download source code - 11.7 KB

Introduction

The WPF TextBox class does not have a built-in option for automatically showing an ellipsis when the text is truncated to fit the visible area. Since I wanted this feature for a project I'm working on, I created my own subclass of TextBox called TextBoxWithEllipsis that does show an ellipsis when appropriate. I also included the ability to place the ellipsis to the left, right, or center of the visible text.

TextBoxWithEllipsis Properties

TextBoxWithEllipsis has the following properties in addition to those inherited from TextBox. I didn't bother to make any of them dependency properties, as I didn't need to for my purposes.

Demo App

The demo app included in the download is a Visual Studio 2010 C# WPF project containing two relevant files:

• TextBoxWithEllipsis.cs - Implementation of the TextBoxWithEllipsis class. You can simply copy this file into your own project, though you'll probably want to change the namespace.
• MainWindow.xaml - The resizable WPF window, shown above, that tests and demonstrates the TextBoxWithEllipsis control.

You can type directly into the "TextBox With Ellipsis" control or enter something in the "Source Text" field and click the button to test programmatically setting the Text property of TextBoxWithEllipsis. The checkboxes and radio buttons are hooked up to the appropriate properties of the TextBoxWithEllipsis control.

The control automatically adjusts the text it displays when it's resized. The ellipsis disappears if the control becomes long enough to accommodate all of the text (in the demo app, the control resizes with the window).

Whenever TextBoxWithEllipsis has the focus, the ellipsis is temporarily disabled so the user can edit, select, or scroll the full text. This behavior is built into the control.

Implementation

The code assumes that if TextBox.ViewportWidth + FudgePix < TextBox.ExtentWidth, the text doesn't fit and an ellipsis is needed. The test is made in the LayoutUpdated event handler. If the text doesn't fit, a binary (or bisection) search is performed by setting the length of the Text property halfway between the last length known to fit and the last length known to be too long. Changing the Text property raises the LayoutUpdated event again, causing the logic to iterate until the maximum length substring of LongText that will fit is found.

The OnTextChanged() method is overridden to prevent the TextChanged event from being raised when the Text property is changed internally (e.g., in the LayoutUpdated handler). Setting Text externally and typing/pasting into the control raises the event as expected.