imageProtocol activation, what is it? Well, when you run “http:{something}” you expect a browser to launch, right? When you type “mailto:{something}” you expect a mail client to launch, right? What if you could create “custom:{something}” that launched your app? That’s custom protocol activation!

MSDN: Windows allows an app to register to become the default handler for a certain URI scheme name. Both desktop and Windows Store apps can register to be a default handler for a URI scheme name. If the user chooses your app as the default handler for a URI scheme name, your app will be activated every time that type of URI is launched. You should only register for a URI scheme name if you expect to handle all URI launches for that type of URI scheme. If you do choose to register for a URI scheme name it is important that you provide the end user with the functionality that is expected when your app is activated for that URI scheme. For example an app that registers for the mailto: URI scheme name should open to a new e-mail message so that the user can compose a new e-mail. For more info on file associations see Guidelines and checklist for file types and URIs.

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