Communication with a user via a bot built with Microsoft Bot Framework is managed via conversations, dialogs, waterfalls, and steps. As the user interacts with the bot, the bot will start, stop, and switch between various dialogs in response to the messages the user sends. Knowing how to manage dialogs in Bot Framework is one of the keys to successfully designing and creating a bot.
At its most basic level, a dialog is a reusable module, a collection of methods, which performs an operation, such as completing an action on the user’s behalf, or collecting information from the user. By creating dialogs you can add reuse to your bot, enable better communication with the user, and simplify what would otherwise be complex logic. Dialogs also contain state specific to the dialog in dialogData.
A conversation is a parent to dialogs, and contains the dialog stack. It also maintains two types of state, conversationData, shared between all users in the conversation, and privateConversationData, which is state data specific to that user.
Every dialog you create will have a collection of one or more methods that will be executed in a waterfall pattern. As each method completes, the next one in the waterfall will be executed.
Your bot will maintain a stack of dialogs. The stack works just like a normal LIFO stack), meaning the last dialog added will be the first one completed, and when a dialog completes control will then return to the previous dialog.
Bots come in many shapes, sizes, and forms. Some bots are simply front ends to existing APIs, and respond to simple commands. Others are more complex, with back and forth messages between the user and bot, branching based on information collected from the user and the current state of the application. Depending on the requirements for the bot you’re building, you’ll need various tools at your disposal to start and stop dialogs.
Dialogs can be started in a few ways. Every bot has a default, sometimes called a root dialog, which is executed when no other dialog has been started, and no other ones have been triggered via other means. You can create a dialog that responds globally to certain commands by using
triggerAction is registered globally to the bot, while
beginDialogAction registers the command to just that dialog. Finally, you can programmatically start a dialog by calling either
replaceDialog, which will allow you to add a dialog to the stack or replace the current dialog, respectively.
When a bot reaches the end of a waterfall, the next message will look for the next step in the waterfall. If there is no step, the bot simply doesn’t respond, naturally ending the conversation or dialog. This can provide a bit of a confusing experience for the user, as they may need to retype their message to get a response from the bot. It can also be confusing for the developer, as there may be many ways a dialog might end depending on the logic.
As a result, when a conversation or dialog has come to an end, it’s a best practice to explicitly call
endConversation both clears the current dialog stack and resets all data stored in the session, except
endDialogWithResult end the dialog, clear out
dialogData, and control to previous dialog in the stack. Unlike
endDialogWithResult allows you to pass arguments into the previous dialog, which will be available in the second parameter of the first method in the waterfall (typically named
Ending a conversation or dialog will also remove the associated state data. This is important to remember when deciding where to store state data. The best practices of minimizing scope of state data apply to bots, just as they do to any other application.
The place where state lifespan becomes trickiest is
dialogData. If you start a new dialog, the dialog doesn’t receive the data from the calling dialog. In addition, when a dialog completes, the previous dialog doesn’t receive the data from the calling dialog. You can overcome this by using arguments.
endDialogWithResult allows you to pass arguments to the prior dialog, while both
replaceDialog allow you to pass arguments into the new dialog.
The sample application we will be building through the next set of examples is a simple calculator bot. Our calculator bot will allow the user to enter numbers, and once they say total we’ll display the total and allow them to start all over again. We’ll also want to allow the user to get help at any time, and to cancel as needed. The sample code is provided on GitHub.
Starting with version 3.5 of Microsoft Bot Framework, the default or root dialog is registered as the second parameter in the constructor for
UniversalBot. In prior versions, this was done by adding a dialog named
/, which led to naming similar to that of URLs, which really isn’t appropriate when naming dialogs.
The default dialog is executed whenever the dialog stack is empty, and no other dialog is triggered via LUIS or another recognizer. (We’ll see how to register dialogs using
triggerAction a little later.) As a result, the default dialog should provide some contextual information to the user, such as a list of available commands and an overview of what the bot can perform.
From a design perspective, don’t be afraid to send buttons to the user to help guide them through the experience; bots don’t need to be text only. Buttons are a wonderful interface, as they can make it very clear what options the user can choose from, and limit the possibility of the user making a mistake.
To get started, we’ll set up our default dialog to present the user with two buttons, add and help. For our first pass, we’ll simply echo the user’s selection; we’ll add additional dialogs in the next section. We’ll do this by setting up a two step waterfall, where the first step will prompt the user, and the second will end the conversation.
One of the biggest challenges when creating a bot is dealing with the fact users can be random. Imagine the following exchange:
This is a common scenario. The user sends a message to the bot. The bot responds. The user gets a new piece of information, in this case their friend is a vegan, and thus asks about a vegan menu. The bot is now stuck, because it wasn’t expecting that response.
triggerAction allows you to register a global command of sorts with the bot, and ensure the appropriate dialog is executed for every request.
In prior versions of Bot Framework, developers typically started every dialog name with /. This was because when registering the default dialog in earlier versions you named it /. As you’ve already seen, that’s not the case starting with version 3.5. As a result, you give your dialog a name that appropriately describes the operation the dialog is built to perform.
bot.dialog is used to register a dialog. The two parameters you’ll provide are the name of the dialog, and the array of methods you wish to execute when the user enters the dialog. Let’s create the starter for add dialog. For now, we’ll leave it with the simple echo, and introduce new functionality as we go forward.
We want to register our AddNumber dialog with the bot so whenever the user types add this dialog will be executed. This is done through the use of
triggerAction, which is a method available on
triggerAction accepts a parameter of type
ITriggerActionOptions has a few properties, the most important of which is
matches. Matches will either be a regular expression to match a string typed in by the user, such as add in our case, or a string literal if the match will be done through the use of a recognizer, such as one from LUIS.
Let’s update our bot to register AddNumber to be started when the user types add. We’ll remove the second step from the default dialog and take advantage of the behavior of our buttons, which will send the text of the button to the bot, much in the same way as if the user typed it themselves.
triggerAction is a global registration of the command for the bot. If you wish to limit that to an individual dialog, use
beginDialogAction, which we’ll discuss later.
triggerAction replaces the entire current dialog stack with the new dialog. While that can be good for AddNumber, that wouldn’t be good for a dialog to provide help. We’ll see a little later how
onSelectAction can be used to manage this behavior.
If you execute the bot at this point you’ll notice clicking Add on the buttons, or simply typing it, will cause the bot to send the message This is the AddNumber dialog. You’ll also notice that help, at present, does nothing. We’ll handle that in a bit.
Let’s talk a little bit about our logic for AddNumber. We want to prompt the user for a number, add it to our running total, and then ask the user for the next number. Basically, we just need to restart the same dialog over and over again. We can use
replaceDialog to perform this action.
In the first step of our waterfall, we’ll check to see if there is a running total available in
privateConversationData, and create one if it doesn’t exist. We’ll then prompt the user for the number they want to add.
In the second step, we’ll retrieve the number, add it to our running total, and then start the dialog over again by calling
replaceDialog takes two parameters, the first being the name of the dialog with which you wish to replace the current dialog, and the second being the arguments for the new dialog. The object you provide as the second parameter will be available in the first function in the new dialog’s waterfall in the second parameter (typically named
It doesn’t make a lot of sense for our bot to have a global total command. After all, it’s only valid if we’re currently adding numbers. Using
beginDialogAction allows you to register commands specific to that dialog, rather than global to the bot. By using
beginDialogAction, we can ensure total is only executed when we’re in the process of running a total.
The syntax for
beginDialogAction is similar to
triggerAction. You provide the name of the
DialogAction you’re creating, the name of the
Dialog you wish to start, and the parameters for controlling when the dialog will be started.
endConversation, we reset the entire conversation back to its starting state. This will automatically clear out any
privateConversationData, as the conversation has ended.
triggerAction will reset the current dialog stack with the new dialog. In the case of AddNumber that’s just fine; the logic on the dialog is designed for the dialog to continually restart. But this is problematic when it comes to Help. Needless to say, we don’t want to reset the entire set of dialogs when the user types help; we want to allow the user to pick up right where they left off.
Bot Framework provides
beginDialog for adding a dialog to the stack. When that dialog completes, it returns to the control to the active step in the prior dialog. Or, in terms of the case of our Help example, it will allow the user to pick up where they left off.
onSelectAction property on
ITriggerActionOptions executes when the bot is about to start the dialog being triggered. By using this event, we can change the way the dialog is started, using
beginDialog, which will add the dialog to the stack instead of replacing stack. The first parameter is the name of the dialog we wish to start, which is provided in
args.action, and the second is the
args parameter we want to pass into the the dialog when it starts. The code sample below will ensure we return control to the prior dialog when this one completes.
beginDialog, don’t hard code the name of the dialog you’re about to start, but rather use
args.action. Otherwise, you’ll notice the dialog won’t actually start.
One of the challenges with the help solution we created earlier is it can only provide generic help; whenever the user types help the exact same message is sent to the user. By using beginDialogAction you can parameters to the triggered dialog, allowing you to centralize messaging for help. In our case, we’ll use the name of the current action as the key to the message we want to send.
If you’ve made it to this point in the article, you already have the skills necessary to create a global cancel operation - you’d add a new dialog, register it with
triggerAction, and add a string match for the word cancel. The dialog would then call
endConversation with a friendly message, and the user would be able to restart he operation.
However, let’s say you wanted to provide granular support for cancel operations, changing the behavior on different dialogs, or maybe not allowing a cancel on a dialog at all. This is where
endConversationAction come into place. Both are tied to a specific dialog, and
cancelAction cancels just the dialog, while
endConversationAction cancels the entire conversation.
The second parameter you’ll pass into cancelAction is
ICancelActionOptions, which includes the
onSelectAction properties we’ve seen before. It also adds
confirmPrompt, which, if set, will prompt the user if they actually want to cancel.
Bot Framework offers many options and methods for managing dialogs and responding to user requests. Harnessing the the power provided by dialogs allows you to create bots that can have conversations with your users that feel more natural.
Thank you to Nafis Zaman for the catch on the behavior of