Question

CaptureDeviceConfiguration.RequestDeviceAccess() method must be invoked by user interaction, otherwise it fails. My question is how does Silverlight know the invocation came from user (i.e. via Button.Click())?

Answer 1

Have a look at this: http://liviutrifoi.wordpress.com/2011/05/18/silverlight-isolatedstoragefile-increasequotato/

Quote:

I was curios though how exactly does silverlight know what a user
initiated event is, but after digging through .net framework source
code I’ve got to a dead end:

if ((browserService == null) || !browserService.InPrivateMode())
{
    //..
}
return false; //means that IncreaseQuota will fail
where browser.IsInPrivateMode is:

[SecuritySafeCritical]
public bool InPrivateMode()
{
    bool privateMode = false;
    return (NativeMethods.SUCCEEDED(UnsafeNativeMethods.DOM_InPrivateMode(this._browserServiceHandle, out privateMode)) && privateMode);
}

where DOM_InPrivateMode is in a DllImport[“agcore”], which according
to microsoft is confidential 🙁 So it looks like I won’t find out soon
how they’re detecting user initiated events, although I’m guessing
they have some centralized private method that detects clicks for
example, and then probably sets a flag that this was indeed “a user
initiated event”, and since you can’t forge clicks or keypresses using
javascript and since you can’t call those private methods using
reflection, it’s “safe”.