Forwarding activities / messages to other dialogs in Microsoft Bot Framework

I have been asked a question a lot recently – is it possible to pass messages / activities between dialogs in Microsoft Bot Framework?  By doing this you could have a root dialog handling your conversation, but then hand off the message activity to another dialog.  One common example of this is using the LUIS service to recognise a user’s intent, but handing off to a dialog powered by the QnA Maker service if no intent is triggered.

Thankfully this is very simple to do.

Normally to add a new dialog to the stack we would use context.call which adds a dialog to the top of the stack. However, there is another method which was added some time ago but is not as widely known, context.forward, allowing us to not only call a child dialog and add it to the stack, but also let us pass an item to the dialog as well, just as if it was the root dialog receiving a message activity.

The example code below shows you how to forward to fallback to a dialog that uses the QnA Maker if no intent is identified within a LUIS dialog.

In the example above, a new instance of the FaqDialog class is created and the forward method takes the incoming message (which you can get as a parameter from the LUIS intent handler), passes it to the new dialog and also specifies a callback for when the new child dialog has completed, in this case AfterFAQDialog.

Once it has finished, the AfterFAQDialog will call context.Done and in the example will pass a Boolean to indicate if an FAQ answer was found – if the dialog returns false then we can provide an appropriate message to the user.

That’s it, it is super simple and unlocks the much asked for scenario of using LUIS and QnAMaker together, falling back from one to the other.

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