Skill: AL Event Binding

Validation Gates

1. After Step 1: Manual codeunit compiles, subscribers don't fire without binding
2. After Step 2: BindSubscription activates subscriber, events fire correctly
3. Final: UnbindSubscription deactivates, no events fire after unbind

Note: Default to StaticAutomatic. Use Manual only for conditional/performance scenarios. Binding is session-specific.

Procedure

Step 1: Create Manual Subscriber Codeunit

codeunit <ID> "<PREFIX> <Entity> Subscribers"
{
    EventSubscriberInstance = Manual;

    [EventSubscriber(ObjectType::Table, Database::<SourceTable>, 'OnAfterValidateEvent', '<FieldName>', false, false)]
    local procedure OnValidate<FieldName>(var Rec: Record <SourceTable>)
    begin
        // Your validation logic here
        if StrLen(Rec.<FieldName>) < 3 then
            Error('<FieldName> must be at least 3 characters');
    end;
}

Step 2: Bind in Context (Page/Codeunit)

pageextension <ID> "<PREFIX> <Entity> Card Ext" extends "<SourcePageName>"
{
    var
        EntitySubscribers: Codeunit "<PREFIX> <Entity> Subscribers";

    trigger OnOpenPage()
    begin
        BindSubscription(EntitySubscribers);
    end;

    trigger OnClosePage()
    begin
        UnbindSubscription(EntitySubscribers);
    end;
}

Common Patterns

Conditional via Setup

procedure ProcessDocument(var SourceRecord: Record <SourceTable>)
var
    AdvancedValidation: Codeunit "<PREFIX> Advanced Validation";
    Setup: Record "<PREFIX> Setup";
begin
    if Setup.Get() and Setup."Enable Advanced Validation" then
        BindSubscription(AdvancedValidation);

    Codeunit.Run(Codeunit::<ProcessingCodeunit>, SourceRecord);
    // Auto-unbinds when procedure ends
end;

Batch Job Optimization

UI subscribers bound only in pages, not in job queue codeunits:

• Page: OnOpenPage → BindSubscription(UINotifications)
• Job Queue: No binding → no UI overhead

Important Notes

Binding behavior:

• Session-specific (Session A binding doesn't affect Session B)
• Auto-dissolves when codeunit instance goes out of scope
• Cannot call Bind/Unbind on StaticAutomatic codeunits (runtime error)

Stale metadata: Recompiling bound codeunit shows error "subscriber is stale" - only during development, not production.

⚠️ Do NOT use Manual for critical business logic that must never be missed.

External Documentation

• EventSubscriberInstance Property
• BindSubscription Method