If you’ve spent anytime developing Silverlight controls for SharePoint that utilise SP.UI.ModalDialog dialogs you may have noticed a idiosyncrasy with the way Silverlight behaves when a modal dialog is thrown from the page that hosts the Silverlight control. The behaviour in IE is that the Silverlight is hidden whilst the modal is visible:
Before throwing a modal – Silverlight control is visible on a page:
During – modal is thrown and Silverlight is hidden:
Once the modal dialog has been closed, the control is made visible again. This presents two issues as far as I can tell, firstly the Silverlight control is actually reloaded when the modal is closed due to a bug. I’ve blogged about this issue including a workaround on this post. Secondly, user context is broken. Depending on the operation your controls is performing, it could be important that the Silverlight controls remain visible whilst a modal dialog is open.
One thing to note is that the behaviour described above is different in Firefox. Here, the Silverlight control remains visible but is not masked by the opaque div that is used to dim the background:
During – Firefox keeps the Silverlight control visible:
So why is the Silverlight control hidden by IE but not by Firefox? The answer is in the out-of-the-box SP.UI.Dialog.js file, or in this example, the SP.UI.Dialog.debug,js file:
Why do this? Well, we’ve worked around the out-of-the-box behaviour of SharePoint modals, Silverlight and IE that hides object tags and our user experience in IE now behaves just like Firefox:
So now in IE and Firefox we see the same behaviour – the Silverlight control remains visible but is not covered by the opaque div used to dim the modal background. 1 line of XAML and 2 lines of C# will fix that.
Next, open the source code of your Silverlight control and append to the end of your control stack (so that it appears over the top of all other controls), a canvas that is the same size as your entire usercontrol:
The important attributes of this canvas are highlighted. The opacity and background colour attributes match those of the out of the box opaque div and the initial visibility is set to collapsed (hidden). Next, in our Silverlight control just before we throw the modal dialog, we make our new canvas visible:
The end result is a visible Silverlight control that has a canvas applied over the top of it that matches the opacity and colour of the out-of-the-box modal background. This ‘fix’ works in both IE and Firefox:
Luckily by adding a canvas to the top of the control stack of the Silverlight control I’m stopping any Silverlight buttons or controls from being clicked. I’m looking at a possible fix for this last issue and will blog further if it works.
I hope this helps someone…