Component triggers

Implement complex behaviour by adding triggers to components

In the same way that flows can have triggers, built-in or custom, components can also have triggers.


A custom component with a custom trigger that matches with palindromes (e.g. radar).


Component triggers can be used to:

  • Improve non-UI integration experiences, like SMS and email.
  • Add a context-sensitive Dialogflow trigger to an email form.
  • Handle unprompted image input during ticket creation pre-chat instead of triggering a catchall flow or a flow with an image trigger.


Component triggers can only be triggered from within a flow when the user is at that step of the flow. In other words, component triggers cannot be triggered from outside of a flow.

Example 1: Built-in component with built-in trigger

Let's take a look at a basic example. By combining a say component with a catchall trigger, we can mimic the behaviour of an ask component. Here's how.

1. Create the flow

In your app's flow folder, create a new file called component_trigger_demo_1.yaml and copy this code into it:

  - keyword: component_trigger_demo_1

  - say: What's your name?
      - catchall
  - say: Hi, (@ flow.result )!

Save the file, then upload it to the Grid by running these commands in your terminal:

meya format
meya push

2. Test it out

Example 2: Custom component with custom trigger

Here is a more interesting example using a custom component and custom trigger. Let's create a custom component that asks the user a question in uppercase letters. It will accept the user's input and continue the flow if they enter a palindrome (e.g. radar), otherwise the flow will end.

1. Create the component

In your app's component folder, create a folder called text. Inside that folder create a file called and copy this code into it:

from dataclasses import dataclass
from meya.component.element.interactive import InteractiveComponent
from meya.element.field import element_field
from meya.entry import Entry
from meya.text.event.say import SayEvent
from typing import List
from typing import Optional

class SayUpperComponent(InteractiveComponent):
    say_upper: Optional[str] = element_field(signature=True)

    async def start(self) -> List[Entry]:
        say_event = SayEvent(text=self.say_upper.upper())
        return self.respond(say_event)

2. Create the trigger

Now let's create the trigger.

In your app's root folder, create a folder called trigger, if it doesn't already exist. Inside, create a folder called text. Within the textfolder, create a file` and copy this code into it:

from dataclasses import dataclass
from meya.element.field import element_field
from meya.text.trigger import TextTrigger
from meya.trigger.element import TriggerMatchResult

class PalindromeTrigger(TextTrigger):
    minimum: int = element_field(default=5)

    async def match(self) -> TriggerMatchResult:
        text = self.entry.text

        if len(text) >= self.minimum and text == "".join(reversed(text)):
            return self.succeed()

3. Create the flow

Finally, let's create a flow that uses the new trigger and component.

  - keyword: palindrome

  - say_upper: Enter a palindrome that's at least 5 characters in length (e.g. radar)
      - type: trigger.text.palindrome
        minimum: 5
  - say: Done

Upload the new code by running these commands in your terminal:

meya format
meya push

4. Test it out

Navigate to your app's simulator and type palindrome to launch the flow. Enter a valid palindrome to watch the flow continue. If you enter a non-palindrome, the flow will end instead.



Consider what would have been involved with implementing this without the component trigger. We would have needed:

  • an ask component to get the user's input,
  • a custom component to check if the input is a palindrome,
  • another step to jump back to the ask component if the user did not enter a palindrome,
  • and a step label before the ask component so we can jump to it.

Component triggers let you add interesting behaviour to your flows while remaining concise.