bcquality/microsoft/knowledge/ui/page-client-expression-must-not-use-in-list.md

bc-version	domain	keywords	technologies	countries	application-area
all	ui	client-expression in-list inlistexpression al0573 al0322 enabled visible editable dynamic-enable	al	w1	all

Page client-expression properties must not use an in [...] list

Description

Enabled, Visible, Editable, and StyleExpr on page controls (the list is not exhaustive; HideValue is rejected the same way) can be bound to a client expression instead of a literal. The documented dynamic forms are a global Boolean page variable, a Boolean field, or a Boolean expression over fields such as "Credit Limit" > "Sales YTD"; plain =/<>/> comparisons combined with and/or/not are valid. An in [...] set-membership test, such as Rec.Status in [Rec.Status::New, Rec.Status::"Needs Review"], is not: the compiler reports it as "InListExpression is not valid for client expressions. Client expressions can only use simple data types and field references."

The severity depends on the control. On a page field the diagnostic is already an error (AL0322). On an action, group, or part it is AL0573, a warning that "will become an error in a future release", so the code still builds and is easy to ship, suppress in a ruleset, or carry forward. A procedure call in the same property position is rejected by the same diagnostics, so moving the list test into a method called from the property does not fix it.

Best Practice

Express the condition in a form a client expression accepts. For a short list, rewrite the membership as an or chain of field comparisons, which keeps the property a live client expression. For a longer or computed condition, evaluate it in AL (an in [...] list is fine there), store the result in a global page Boolean variable, and bind the property to that variable. Recompute the variable wherever its inputs change: OnAfterGetCurrRecord when the current record changes, and the OnValidate of each page field the condition reads for in-place edits. Do not use OnAfterGetRecord for action, group, or part state: it runs once per row loaded, so on a List or Worksheet page the variable ends up reflecting the last fetched row rather than the selected one (see OnAfterGetCurrRecord is not per row). OnAfterGetRecord is right only for per-row field state inside a repeater.

For Visible on field and action controls, the Visible property documentation requires the variable to be resolved in OnInit or OnOpenPage; do not rely on per-record recomputation to show and hide those controls. Enabled and Editable have no such restriction. See sample: page-client-expression-must-not-use-in-list.good.al.

Anti Pattern

A page or pageextension control property Enabled, Visible, Editable, or StyleExpr whose value contains in [, typically an enum or option field tested against several values. Reviewer signal: the in [ token appears directly in the property value rather than inside a trigger or procedure body. Replacing it with a call to a procedure that performs the same test is the same defect in a different shape.

Do not flag plain comparisons joined with and/or, such as Enabled = (Rec.Status = Rec.Status::New) or (Rec.Status = Rec.Status::"Needs Review");; they compile cleanly and Microsoft uses them, for example in BCApps AccountantExpenseReports.Page.al and AgentTaskLogEntry.Page.al. Do not flag in [...] used inside procedures or triggers that assign a Boolean variable. See sample: page-client-expression-must-not-use-in-list.bad.al.

References

• Enabled property: dynamic values are a Boolean variable, a Boolean field, or a Boolean expression such as "Credit Limit > Sales YTD"; variables must be global page variables.
• OnAfterGetCurrRecord (Page) trigger: in a page with a repeater, called only when the current record is updated, after all OnAfterGetRecord calls for the rows.
• Visible property: variables for field and action controls must be resolved by OnInit or OnOpenPage.
• Compiler warning AL0573 and compiler error AL0322. The Learn pages show only the {0} template; the compiler's message for this case is "InListExpression is not valid for client expressions. Client expressions can only use simple data types and field references." (AL compiler 30.0: AL0573 for action, group, and part properties; AL0322 for page field properties, including HideValue).
• Comparison-based client expressions in BCApps, for example Enabled = Rec.Status <> Rec.Status::Running; in BCPTSetupCard.Page.al. BCApps contains no page client expression that uses an in [...] list.
• Global Boolean recomputed on current-record change in BCApps: EDocumentLogs.Page.al, a List page, binds Enabled = IsExportEnabled; and sets IsExportEnabled in OnAfterGetCurrRecord.
• Or-chain client expressions in BCApps: Enabled = (Rec.Status = Rec.Status::"Pending Approval") or (Rec.Status = Rec.Status::"Interim Approved"); in AccountantExpenseReports.Page.al and Visible = (Rec.Type = Rec.Type::"Output Message Draft") or (Rec.Type = Rec.Type::"Output Message"); in AgentTaskLogEntry.Page.al.