An Extended WPF TabControl

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Introduction

I recently decided to have a go at changing the built-in WPF TabControl so that it behaves similar to the way in which Internet Explorer 7 works.

The main area I wanted to change was the way in which the TabItems are arranged, currently the built-in TabControl will pack and stack items, so the more items there are, the more room is required for the headers, taking up space from the actual content of the TabItem.

With Internet Explorer 7, tabs remain on a single row and will scroll in and out of view. This is the way I wanted this control to behave.

Properties/Events

There are a few extra properties (Dependency Properties) and events added to the control.

• AllowAddNew - Setting this property to true will allow the end user to add new tabitems to the control via a button.
• AllowDelete - Setting this property to true will allow the end user to delete tabitems from the control by clicking on the close button on the selected tabitem.

If the above properties are set to true, there are three events that go with these properties. They are TabItemAdded, TabItemClosing and TabItemClosed: all provide a reference to the TabItem being added/removed, the TabItemClosing event providing a place to cancel the close if required.

• AddNewTabToEnd - If this property is true, tabitems added using the AddNew button will be added to the end of the row of tabitems, otherwise the new tabitem will be inserted immediately after the current selection.
• SelectNewTabOnCreate - If this property is true, focus will be moved to the new tabitem when added.

Finally, there are three extra properties of type Brush which are used for coloring the tabitems based on their state:

• TabItemNormalBackground
• TabItemMouseOverBackground
• TabItemSelectedBackground

If you look at the picture at the top of this article, it shows the default style for the TabControl. I've intentionally made this very basic. By just using the extra Background properties, you can easily change the appearance of the TabControl. As this picture shows, by adding a few LinearGradientBrushes, you can get something that resembles Internet Explorer 7.

There are four properties which take an active part in the arrangement of the tabitems. They are:

• TabItemMinWidth
• TabItemMaxWidth
• TabItemMinHeight
• TabItemMaxHeight

Arranging the TabItems

There are three ways in which the tabcontrol arranges its tabitems.
The following description is relevant if the TabStripPlacement property is set to Top or Bottom.

1. If the combined widths of the TabItems is less than the available visible space, then we just arrange them one after the other, taking into account the TabItemMaxWidth and TabItemMinWidth properties.
2. If the combined widths are greater than visible, then calculate the width required for all the tabitems so that all are visible. If this width is greater than the TabItemMinWidth property, then we arrange the tabitems using this calculated width.
3. Once we add too many tabitems that their widths would be less than the TabitemMinWidth property, then scrolling will be enabled.

The class that is responsible for arranging the tabitems is the VirtualizingTabPanel. As the name suggests, this panel derives from the VirtualizingPanel class and implements the IScrollInfo interface. I won't describe here what a VirtualizingPanel is, instead I will just direct you to this Blog post by Dan Crevier which describes what it is and how to implement one.

Using the Code

To use the control, you will need to add a reference to the Wpf.TabControl assembly, then add an xmlns to the window:

xmlns:r="clr-namespace:Wpf.Controls;assembly=Wpf.TabControl" 

The demo provided shows how to add the control to a window and set its properties.

History

• 13-Oct-2007: Initial upload
• 09-Mar-2009: Implemented ItemsSource binding & bug fixes
• 05-Apr-2009: Updated source code