Silverlight 4 and COM/ActiveX Integration

Silverlight 4 supports COM/ActiveX controls with Trusted permissions. However you must configure your app to be an Out-of-Browser app with Trusted permissions.

Here is the snippet of code that will open Excel and place a value in the first cell:

dynamic ex = AutomationFactory.CreateObject("Excel.Application");
ex.Visible = true;
ex.workbooks.Add();

dynamic sheet = ex.ActiveSheet;
sheet.Cells[1, 1].Value = "hello!";

However this won’t compile out of the box. First make sure that your app is enabled to run as an Out-of-Browser app. Open up your project properties and on the “Silverlight” tab make sure that “Enable running application out of the browser” and then click the button “Out-of-Browser Settings…” and at the bottom check “Require elevated trust when running outside the browser.”

If you’ve read other tutorials, you’ll see that a lot of them are using ComAutomationFactory. This is because these tutorials were written with a beta release of Silverlight 4. That’s why you’re getting this error:

The name 'ComAutomationFactory' does not exist in the current context


Change “ComAutomationFactory” to “AutomationFactory” and you’ll still notice that it won’t compile. Now you’re probably getting this error:

The name 'AutomationFactory' does not exist in the current context


ComAutomationFactory was previously in the namespace System.Windows.Interop. AutomationFactory has been moved to System.Runtime.InteropServices.Automation.

Now you might be getting the following error:

One or more types required to compile a dynamic expression cannot be found. Are you missing references to Microsoft.CSharp.dll and System.Core.dll


All you need to do is add a reference to “Microsoft.CSharp.dll.” You can do this by right-clicking “References” in the “Solution Explorer” and then navigating to the “.NET” tab and selecting it.

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-JP