Event Triggering Order in Panels

This documentation is valid for:
GeneXus 18 Help
GeneXus 17 Help

This document explains the order in which events are executed in a Panel for Android and iOS applications, including components, Global Events, and application lifecycle events such as ApplicationPause, ApplicationResume, and Back.

Understanding this sequence helps developers design predictable data flows, avoid redundant server calls, and coordinate communication between nested components.

Execution Flow in Panels

When a Panel is executed, a specific sequence of client and server events takes place. These events determine how and when UI initialization, data loading, and updates occur.

Order	Event	Context	Description
1	ClientStart	Client	Runs once on the device when the Panel is first opened. Used to initialize variables, UI controls, and access device capabilities.
2	Navigation.Start	Client	Runs after ClientStart when the navigation style requires it (Slide, Tab, Flip, etc.).
3	Start	Server	Executes once. Used for data initialization, service calls, or loading fixed information into variables.
4	Refresh	Server	Runs after Start. Used for dynamic data updates or variable recalculation.
5	Load	Server	Runs last, once per record if the grid has a Base Table, once if it has no base table, and not at all if the grid is SDT-based.

For example: Panel opens → ClientStart → Navigation.Start → Start → Refresh → Load

Manual Refresh

You can manually trigger a refresh using the Refresh() command from any client event. If the data context has changed, the Refresh and Load events are executed again. Otherwise, no server request occurs.

Note: Use Parm() rules with filters to force reloading.

Panels with Components

When a Panel contains components, each component executes its own independent event sequence immediately after the main Panel’s events finish.

Sample:

MainPanel.ClientStart
MainPanel.Start
MainPanel.Refresh
MainPanel.Load
├── ComponentA.ClientStart
│   ├── ComponentA.Start
│   ├── ComponentA.Refresh
│   └── ComponentA.Load
└── ComponentB.ClientStart
    ├── ComponentB.Start
    ├── ComponentB.Refresh
    └── ComponentB.Load

Global Events (Component Communication)

Global Events allow components to communicate inside a Panel without having direct references to each other. They use the predefined external object GlobalEvents, which works as an event bus within the same screen.

Usage Example:

Event ItemUpdated(&ProductId)
EndEvent

Event &Update.Click
   GlobalEvents.ItemUpdated(&ProductId)
EndEvent

Event GlobalEvents.ItemUpdated
   Refresh()
EndEvent

Lifecycle Events (Background and Foreground Transitions)

When a mobile application transitions between background and foreground, GeneXus executes application lifecycle events that allow you to manage state restoration or data updates.

Event	Trigger	Platform	Behavior
ApplicationPause	Applications goes to background.	Android & iOS	Executes once in the visible Panel. Used to save state, stop timers, or pause animations.
ApplicationResume	Application returns to foreground.	Android & iOS	Executes before interaction resumes. Used to refresh or synchronize data.
Back	User navigates back.	Android & iOS	Captures hardware button or gesture. If not handled, it performs default navigation.

Sample

Event ApplicationResume
    Refresh()
EndEvent

Full sample: Complex Flow

This sample shows a complete execution flow for a Panel with Components and Global Events:

1. The user opens ProductPanel → ClientStart → Navigation.Start → Start → Refresh → Load
2. Two components (ProductInfo and ProductList) execute their full cycles.
3. The user marks a product as favorite in ProductList, triggering GlobalEvents.FavoriteUpdated().
4. ProductInfo listens and executes Refresh → Load.
5. The user switches to another application → ApplicationPause executes.
6. The user returns → ApplicationResume executes → Refresh() updates data.
7. The user presses Back → Event 'Back' executes, controlling navigation.

Event execution order in Panels

Event	Context	Frequency	Purpose
ClientStart	Client	Once	Initialize UI and device state.
Navigation.Start	Client	Once	Navigation-specific setup.
Start	Server	Once	Initialize data and variables.
Refresh	Server	Multiple	Reload data dynamically.
Load	Server	Per record	Populate Grids.
GlobalEvents	Client	On demand	Communicate between Components.
ApplicationPause	Client	On demand	Save UI state.
ApplicationResume	Client	On demand	Restore or sync data.
Back	Client	On demand	Handle navigation or exit.

Event handling best practices for Panels

Use ClientStart event for visual setup and device logic.
Use Start and Refresh events for data loading and filtering.
Use Parm() rule to force refresh when filter variables change.
Handle ApplicationPause and ApplicationResume events for continuity.
Use GlobalEvents to synchronize components.
Use Components designed to be idempotent (safe to reload).