We recommend implementing this feature for mobile and desktop SDKs.

UI event transactions are enabled by setting the SDK config option enableUserInteractionTracing, which we recommend enabling per default. Remember that this feature will generate many transactions, which can significantly impact running out of quota. Therefore, it might be safer to disable this feature per default when adding it and enable it per default in an upcoming major SDK release.

UI event transactions aim to capture transactions based on user interactions, such as clicks, scroll events, pinches, etc. The UI events the SDK can hook into might vary depending on the platform. UI event transactions are an expansion to transactions generated automatically by the SDK, which are referred to as auto-generated transactions in this document.

Creating transactions for a single UI event without any spans would be fruitless. Instead, the SDK shall use a UI event as the entry point to a possibly meaningful transaction. It should wait to see if it can add any auto-generated spans to the transaction. If it can, it shall keep and send the transaction. If not, the SDK should discard the empty transaction. A combination of two concepts is needed to implement the wait-and-see logic: idle transactions and wait-for-children. Check out the specification below to see how those two concepts work together with covering multiple edge cases. The following description is drastically simplified:

• Idle-transactions: The SDK schedule an idle timeout for the transaction when starting it. When the transaction or any of its spans starts a new span, it resets the timeout. The SDK finishes the transaction when the timeout succeeds.
• Wait-for-children: A transaction waits for all its child spans to finish before finishing itself.

Before diving into the specification with all the edge cases, let's look at two simple examples:

1. The user clicks a button that triggers some requests to the backend and stores data in the local database. The SDK can create a meaningful transaction in that case.
2. The user clicks a button that solely validates some form data and triggers nothing that the SDK can automatically instrument. The SDK could only create a transaction without any spans, which would be valueless.

Specification

Users can change the idleTimeout via the SDK config options. The default is 3.0 seconds.

The specification is written in the Gherkin syntax.

Scenario: Starting UI Event transactions
    Given an instrumentable UI event
    Then the SDK starts a UI event transaction 
    And schedules to finish the UIEventTransaction with
     the idle timeout of the options

Scenario: Wait for children when starting span
    Given a UI event transaction
    When the SDK starts a child span
    Then the SDK cancels the idle timeout
    And waits for the child to finish

Scenario: Schedule idle timeout when the last span finishes
    Given a UI event transaction
    And the transaction has one or multiple running child spans
    And the transaction is waiting for its children to finish
    When the SDK finishes the last child span
    Then the SDK schedules the idle timeout 

Scenario: Discard UI event transactions without child spans
    Given a UI event transaction
    And the transaction has no child spans
    When the idle timeout times out
    Then the SDK discards the transaction 

Scenario: Set time to last finished child span
    Given a UI event transaction
    And the transaction has one finished child span
    And the transaction has one running child span
    When the running child span finishes
    Then the SDK schedules the idle timeout
    And the SDK finishes the transaction after the idle timeout
    And trims the end time of the transaction to the one of the last finished
        child span

Scenario: Don't overwrite existing status of UI event transactions
    Given a UI event transaction
    And the UI event transaction has a status
    When the SDK finishes the UI event transaction
    Then it keeps the status 
    And doesn't overwrite it

Scenario: Same UI element with same event
    Given an ongoing UI event transaction
    When the user triggers the same UI event with the same type for the same
        UI element
    Then the SDK reschedule the idle timeout
    And doesn't create a new transaction

# If your SDK binds auto-generated transactions to the scope see binding
# to scope
Scenario: Same UI element with different event
    Given an ongoing UI event transaction
    When the user triggers the same UI element with a different event
    Or the user triggers a different UI element
    Then the SDK finishes the ongoing transaction
    And sets the status to OK
    And waits for the children to finish
    And cancels the idle timeout
    And starts a new transaction

Binding to scope

On platforms mainly interacting with the static API, such as mobile, it's typical to bind auto-generated transactions to the scope so that users can access them via the static API. We recommend binding UI event transactions to the scope on these platforms. The following extra rules apply as UI event transactions could interfere with other auto-generated transactions.

The SDK adds auto-generated spans to the transaction bound to the scope. UI event transactions need auto-generated spans not to be empty. Therefore, the SDK shouldn't start a UI event transaction if there is already an ongoing screen load/navigation transaction or a transaction bound to the scope by the user.

Scenario: Same UI element with different event
    Given an ongoing UI event transaction
    When the user triggers the same UI element with a different event
    Or the user triggers a different UI element
    Then the SDK finishes the ongoing transaction
    And sets the status to OK
    And waits for the children to finish
    And cancels the idle timeout
    And removes the ongoing transaction from the scope
    And starts a new transaction
    And puts the new transaction on the scope

Scenario: UI event triggered but transaction ended
    Given an auto-generated transaction from any UI event
    And the transaction is already finished
    When the user triggers the same UI event
    Then the SDK starts a new UI event transaction

Scenario: Manually created transaction bound to the scope
    Given an ongoing manually created transaction by the user bound to the
        scope
    When the user triggers a UI event
    Then the SDK doesn't start a UI event transaction

Screen load/navigation transactions

This section deals specifically with auto-generated transactions for loading screens. If your SDK has other types of auto-generated transactions, please update the specification here.

Scenario: Ongoing UI event transaction
    Given an ongoing UI event transaction
    When the SDK creates a new screen load transaction
    Then the SDK finishes the ongoing UI event transaction
    And removes it from the scope
    And sets the status to canceled
    And waits for its children to finish

Scenario: Ongoing screen load/navigation transaction
    Given an ongoing screen load/navigation transaction
    When the user triggers a UI event
    Then the SDK doesn't start a UI event transaction

Transaction name

The user should be able to identify to which UI element the UI event transaction belongs on which screen by only looking at the transaction name. Choose whatever works best for your specific platform. Be attentive not to use any PII in the transaction name. One recommendation is
screen name + view identifier. On Android, this would map to LoginActivity.login_button, and on Cocoa, to YourApp.LoginViewController.loginButton. If the UI element doesn't have a view identifier, it's acceptable that the SDK doesn't start a UI event transaction and logs a warning to inform the user. The Cocoa SDK uses the method the UI element calls as the view identifier.