In this blog post I present a simple attached behaviour that uses a Thumb control within a Popup to adorn any UI element so that the user can re-size it.
A simple feature that has become quite popular on the web is to attache a small handle to text areas so that the user can resize them, this is useful if a user wants to add a large piece of text to a small comment form for example. Interestingly the Google Chrome browser makes all text areas resizeable by default, which leads to web developers wondering how to turn this feature off for their website. I thought that this was a pretty useful feature, so decided to implement a little attached behaviour that would do the same think for Silverlight:
You can make any element resizable by setting the following attached property:
The implementation of this behaviour is pretty straightforward. When the Attach property changes, i.e. when it is set on an element a Thumb and a Popup are created:
A static dictionary is used to relate the elements which have this property set o their respective Popup. The Thumb is styled via a Style which is looked up from the application resources. The following style re-templates the Thumb, replacing its visuals with an image:
Whenever the element changes size we need to reposition the Popup so that the thumb always remains on the bottom-right edge of the element:
And finally, when the thumb is dragged, we resize the element to which it is associated:
I am Technology Director at Scott Logic and am a prolific technical author, blogger and speaker on a range of technologies.