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Interop Compatibility

There are several issues in general when embedding interop controls (such as WinForms, ActiveX, etc. controls) in docking window content. This topic discusses some of the ways Actipro Docking & MDI has been designed to improve compatibility with interop controls.

The two primary issues are:

  • Interop content is always rendered on top of WPF content in the same root window (a.k.a. the airspace issue).
  • Interop content doesn't always raise WPF focus-related events properly.

Quick Summary

If you don't wish to read the details below, the way to enable maximum compatibility with interop controls is to:

Read the following sections for more information on interop compatibility.

Using Non-Hosted Popups

Due to the airspace rendering issue mentioned above, if your application will host interop content, set the DockSite.UseHostedPopups property to false. Setting that to false will allow auto-hide popups and splitters to properly appear above interop content.

This will also allow interop content to appear properly in the auto-hide popups because it will disable auto-hide popup animation, which sometimes causes rendering glitches in interop controls.

If you do not plan on having interop content in your application, we recommend leaving the UseHostedPopups property as its default value of true.

Live Splitting

By default, live splitting is enabled meaning that there is no preview highlight when dragging a splitter. The surrounding containers are immediately resized during splitter drags in this mode.

Sometimes this mode doesn't work well with interop controls since they could have glitchy rendering as they are resized. It's recommended to disable live splitting by setting the DockSite.IsLiveSplittingEnabled property to false. In that mode, the splitters in the dock site will only resize the content when the drag operation has been completed. A preview of the split location is shown as the user drags to indicate the relative sizes of the content if the user releases the pointer. This allows complex UI to only be rendered once, after the drag operation is completed.

Handling Focus Issues

There are known issues in core WPF with how it tracks and reports focus movement in and out of HwndHost. This makes it difficult to use standard WPF-based focus events when dealing with HwndHost-based scenarios, because the events aren't raised properly.

We provide a workaround for most of these issues in the form of an InteropFocusTracking.IsEnabled attached property that should be set on any HwndHost-based control, such as WindowsFormsHost, WPF WebBrowser, etc. Set that attached property to true on such controls in your docking window hierarchy to enable our workarounds.

Impact of Transparent Backgrounds on Performance

As a quick aside, we've noticed in certain scenarios that if you wrap a WindowsFormsHost with a control that has a Transparent background, core WPF can cause performance degradation in layout cycles due to how it's attempting to blend backgrounds with interop content. This sample XAML code shows the scenario:

xmlns:winforms="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"
...

<Border Background="Transparent">
	<WindowsFormsHost docking:InteropFocusTracking.IsEnabled="True">
		<winforms:WebBrowser Url="http://www.actiprosoftware.com" />
	</WindowsFormsHost>
</Border>

If the Background is left with its default null value, or is set to a solid color, performance is significantly better. This can occur anywhere in WPF (not just the Docking/MDI product), and we wanted to pass along the tip.

It's important to note that ToolWindow, DocumentWindow, and Workspace have a transparent background by default. Therefore, any WindowsFormsHost control in them should be wrapped with a Border that has a solid background set. Or alternatively, set the Background properties of those controls to a solid brush.

Some side effects of using transparent backgrounds around WindowsFormsHost may be seeing the size of the control resize and paint itself before the location of the control is updated and repainted, thereby creating a flicker effect.

How to Embed WinForms Content in a Docking Window

This sample XAML code shows how to create a document window that contains a Windows Forms WebBrowser control embedded in it. Note that any WinForms controls must be wrapped with a WindowsFormsHost. Set the attached InteropFocusTracking.IsEnabled property on the WindowsFormsHost. And set a solid brush background on the containing control to prevent layout performance issues.

xmlns:winforms="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"
...

<docking:DockSite>
	<docking:Workspace>
		<docking:TabbedMdiHost>
			<docking:TabbedMdiContainer>
				<docking:DocumentWindow Title="Document1" Background="{DynamicResource {x:Static themes:AssetResourceKeys.ContainerBackgroundLowBrushKey}}">
					<WindowsFormsHost docking:InteropFocusTracking.IsEnabled="True">
						<winforms:WebBrowser Url="http://www.actiprosoftware.com" />
					</WindowsFormsHost>
				</docking:DocumentWindow>
			</docking:TabbedMdiContainer>
		</docking:TabbedMdiHost>
	</docking:Workspace>
</docking:DockSite>